4 Speed and 5 Speed Transmissions
Output shaft snap ring (circlip) &
groove problem; serial numbers versus model year;
pawl spring breakage; neutral switches; shift kits; input shaft seal; kickstarter; throw-out
bearings; shift linkage; bearings, hints on shifting smoothly (preloading the shift lever and why), gear ratios, ETC.
Noisy rattles sounds
Doing it yourself AND recommended repair specialists.
© Copyright, 2014, R. Fleischer
Many folks have problems
understanding, let alone visualizing how a BMW transmission operates.
I am putting links at the beginning of this article to help you with that understanding.
Link #1: This shows how a typical transmission, in this case a drum type cam similar to a Classic K bike, might shift: www.gadgetjq.com/transmission.htm An Airhead shifts similarly except that the shift levers are moved by a flat plate cam.
Link #2: This shows BMW GS transmission. Well worthwhile to review this for information on shifting and various noises, etc. http://micapeak.com/bmw-gs/trans.html
Link #3: http://w6rec.com/duane/bmw/trans/index.htm Some information how a transmission works, but the bulk of the information in Duane's article is for the /2 and later transmission problems, testing, and many more details. MUCH of the information is NOT covered in my own transmission article, below, that you are reading. It is a very worthwhile read. I have some nitpicking with some of the information, mostly not worth relating here. The article does describe the broken clutch lever pin problems, and you will find the the exact part numbers and information in my own clutch article for your Airhead. See also my item #14 (below) on the roller.
NOTE that Duane's article does not cover a LOT of what I do, below, and certainly does not cover how to actually overhaul a transmission, how to shim it, nor ANYthing about the 17.5° gear angle change, etc.
I have recommended in the past that you use ONLY a quality petroleum GL5 oil in the transmission, and preferably in grade 80W90 for most all conditions. I also said that you could use 75W90 or 85W90. There are oils available that replace the "90" with 120 or even 145 but I recommended that you do NOT use them unless you live in an area where the temperature that you start the bike at will be ~100°F or more, and that you will be riding relatively fast or with heavy loading, or pulling a sidecar or trailer....all in VERY hot weather...again, that means consistently over 100°F.
I have changed my mind on several things. My present recommendation is that you use a synthetic gear oil of very high quality. It is my belief that it will extend transmission time before overhaul by a very considerable amount. NOTE that you must NOT use any additive with synthetic oil, such as the Dow Corning additive. I am presently recommending only the Spectro brand, in 75W90, in the type called "platinum". Use it in the transmission and the rear drive of Airheads and Classic K bikes. I have no objection to it being used in the driveshaft (of those models using oil there).
Any oil will thin and thicken with temperature changes on its own 'chart curve'. How this happens is a property of the base oils and additives. Using a thicker (higher viscosity) oil ending in 120 or 140 or even 145, will/might take the transmission well out of the design operating area, as far as gears and parts speeding up and slowing down during shifting, thus gear changing up and down can be different. Restating this: the difference is in spin up and spin down time for shifting. I am also concerned that, when colder than ~100°F air temperature, and at colder start-up, lubrication is possibly reduced, protection could be decreased and there are other not-so-nice things. If you use, example, a 80W145, then the oil at any normal operating temperature will ALWAYS be thicker than if the oil was a 80W90. This may NOT be a bad thing for very hot climates and hard usage, but for most riders I think some caution is needed. I would certainly NOT use a petroleum-based oil in such a wide viscosity range, in moderate to colder climates.
There is a rating called Viscosity Index, different with all oils, depending on version, weight, manufacturer, etc.....that has to do with the rate of viscosity change of the oil with temperature change. A straight weight oil, such as SAE 80, will thin much more, than a 80W90, as temperature rises. The base stock and the additives control this. BMW wants you to use what it specifies. That's generally a very good idea....but I have set down earlier, above, what my thoughts are. NOTE: Better oils ARE now available, compared to when your bike was made.
There is NO question in my mind anymore that SYNTHETIC GL5-rated oils will, or can, PROLONG the life of your transmission (and rear drive). That does not mean that they should always be used; but I think they are now good enough for me to recommend them instead of dino oils. Note that in some instances, the seals and the oil may not be perfectly compatible. If you change from a dino to a synthetic, and get some weeping or leaks, change to another type/brand of synthetic, or go back to a dino. Seals have varied in materials over the years, with the same part number. I believe the transmission and rear drive oil should be changed every 10,000 to 15,000 miles; with the synthetics going towards the higher figure. I believe it will pay you over the long run to change more often than the books say. I am using more and more high quality synthetic gear and engine oils these days...they have proven themselves.
Transmission rattling noises
This section was added in May, 2013, prompted by an inquiry, and my answer, on the Airheads LIST. It is being placed near the beginning of this long transmission article, purposely, as this question comes up relatively regularly. It is edited from the original, for clarity.
"I noticed a noise the gearbox makes at low idle. I know it is the gearbox because the noise disappears when the clutch is engaged. I can also hear it when putting my ears next to the gearbox when the bike is
on its stand. I am pretty sure this noise existed before but maybe I grew used to it. It is a rattle or clack/clack rotating kind of noise."
It is NORMAL for Airheads to have a gearbox rattle with hot oil, and at idle, and usually not rattle with cold thicker oil. Old Airheads were pretty noisy. Worse as various bits and pieces wear. It is not in the slightest a problem, USUALLY.
It typically sounds worse if the carburetors are out of sync, or anything that allows the cylinders to be a bit unbalanced in operation. This includes irregular ignition timing....rather common on the pre-1979 models. That irregular ignition timing can be seen with an ignition-fired strobe light shining on the timing hole. There will be double images. That can come from timing chain sprocket wear, or other associated items, like the chain, guide, etc.
The cam that operates the valves is a jerky load on the timing chain...that in itself can cause irregular power pulses, primarily but not exclusively from irregular ignition pulses. A bent cam tip, even as little as 0.001", can cause irregular ignition timing and is not unusual. The irregular power pulses cause the engine to not rotate smoothly, that causes jerkiness on parts in the transmission, causing the "Airhead Rattle".
The tell-tale sign is that the noise goes totally away when you pull-in the clutch lever at the handlebars and, typically, tends to go away if you raise the idle rpm with the throttle just a bit.
Do NOT have the engine idling too slow. Some books may show as low as 800 rpm. Back in the old days of heavy flywheels, especially on the R50 or R60 models, it was common for folks to brag about how smooth and silent their Airhead engine was at idle. UNfortunately, trying to idle the engine so low (many would try for 600 rpm, let alone 800), is BAD for the engine; particularly a worn engine. I highly suggest 1025 rpm. If the idle is too slow, oiling to the chain and sprockets will likely be low enough to accelerate wear on those items. The only oil they get is from the hole in the oil pressure regulator, and if the oil is hot and thin and idle rpm is low, then oil pressure is low, there is no oiling. The pressure regulator needs 75 psi or more to operate, which means some oil coming out of it. Thin hot oil, worn bearings, etc....contribute to low oil pressure, as does low rpm ...as that means lower rpm on the oil pump rotor.
The timing chain area items are NOT the only items in the engine that will have adverse wear with too low an idling rpm. The Airhead Rattle is more likely on an older high mileage engine...which has more loss of oil pressure from worn bearings, etc. Airhead rattle is LESS likely, or less noisy, on models from 1979 due to the improved ignition stability (cam drive to the ignition is much improved), and somewhat better chain tautness control.
IF you are still worried, wait until the engine AND transmission is cold. Have a friend help you if you are not dexterous; or, just do this at transmission oil change time when you are draining the oil anyway. Assuming not changing oil: unscrew the transmission drain bolt. Be prepared to stick a cork or another finger in the transmission instantly, to avoid loosing more than a tablespoon or two of transmission oil. This will allow you to not have to purchase another quart or liter of oil...of course, if the oil is relatively new, you could also just drain it into a clean container, and reuse it. Put #1 eyeball on the magnetic drain plug. If there is anything more than soft fuzz felt between your fingers, then there is a problem. NO SHARP PARTICLES NOR PIECES should be felt. If there is anything small and sharp, you may (or may not!) be safe for a reasonable amount of riding to where the transmission can be opened. Anything large?....take an in-focus close-up photo, post it in at a free hosting site on the Internet, then inquire on the AIRHEADS LIST, with a link to the photo.
The rest of this article begins with a VERY LONG section about 5 speed transmission bearing & circlip problems.
Transmission problems, checks, and testing:
What are some simple checks and tests you can do to determine if your 5 speed transmission has a problem developing?
(1) AFTER a 10+ mile ride to THOROUGHLY warm up the engine and transmission, in 5th gear
and maybe 5500 rpm or so, suddenly whack the throttle wide open. If you feel some vibration
that is unusual, for SURE you want to do all the tests below, as the forward bearing on the
output shaft may be disintegrating.
(2) Whether or not test (1) shows anything, jack or otherwise block the rear wheel so it is slightly
off the ground. With engine off, in neutral, spin the rear wheel by hand as fast as you can and
listen to the gearbox. This spins the output shaft bearings only. NO bearing noises should be
heard. I prefer to do this with the transmission hot from a ride.
(3) Start the engine (this is with hot engine and transmission) and let it idle in neutral. Pull the
clutch in for a few seconds and then let it out. When the clutch then engages, this spins the input
shaft and cluster shaft bearings only. There should not be a bunch of bearing noise when you
let the clutch out (you may hear some normal clutch spline chatter).
(4) Engine off, transmission in neutral, rotate the rear wheel forward SLOWLY. This is best
done with transmission hot from riding. ZERO roughness and NO notchiness must be felt.
After that is done, I do recommend you go further, and that is to unbolt the driveshaft from the
output flange of the transmission and rotate that flange with fingers. ANY notchiness is cause for
the transmission to be overhauled. Now do another test, best done with bolts in the flange, to grab
onto. Try to move the flange in and out. ANY free play is likely caused by internal PROBLEMS.
(5) The transmission output flange has 4 special bolts, and they are NOT to be used with any type of
lockwasher, contrary to books or what you may be told. The thread length of the latest PROPER
bolts are slightly shorter, as the old split lockwasher and longer bolts should be eliminated.
There is information on this website about that: Drvshtboltstoolstorque. I suggest you read that
article. The threads should be cleaned, and then a drop of Loctite BLUE applied, and tighten to 29
foot pounds. There are various methods of enabling use of a torque wrench here. You can just give
the bolts a good grunt with a short 12 point wrench; or, torque them properly.
See ALSO my TOOLS article on this website.
These are important tests, as usually a problem shows up with these tests, even if there is nothing much on the magnetic drain plug.
(6) Inspect the transmission drain plug, which has a magnetic center. If the transmission is
quite COLD when this is done, and you are quick about it or have three hands and extra fingers to
plug the hole, you can loose hardly a tablespoon of oil (otherwise, drain and collect it).
Inspect the drain plug. A modest amount of FUZZ, soft-feeling, is fine. ANY feelable sharp
particles are cause for further inspection. NOTE that fairly large amounts of FUZZ,
soft-feeling, after maybe only a few thousand miles since an oil change (and fuzz removal), CAN
indicate that the transmission is failing....and for the circlip-less versions, indicate that the 5th gear
bearing is deteriorating, and the transmission really should be overhauled and the circlip installed.
All the above tests are not necessarily 100% conclusive, and later in this article are some
other tests, so do NOT stop reading HERE!
What are some common things that are not usually a transmission failing problem?
(1) Small amounts of 'fuzz' on the magnetic drain plug, seen at every scheduled (20K-30K?) gear oil
change. The fuzz will NOT have sharp particles. The fuzz is paste-like, and smooth feeling.
(2) Rattling noise from gearbox in neutral, at idle rpm, after thorough warm-up.
(3) Shifting problems, especially from 2nd gear downward. This usually means that your input splines
need lubrication (unplated early shafts tend to need cleaning and lubrication at 15,000 mile intervals,
nickel plated shafts at maybe 25K).
(4) Shifts not always made. Check the screw in the shift arm...they are known to loosen. Use Loctite
BLUE. Perhaps your boot tips are overly thick....reset the linkage, or adjust the footpeg.
The Circlip problem applies TO ONLY SOME 5 speed transmissions.
OVERVIEW of the circlip
From sometime near the end of the 1984 production year (no longer do I think this began at the beginning of the 1985 production year), BMW's transmission maker made a modification to the transmission. On the output shaft, they left out a snap ring (circlip) & shortly thereafter (?) they no longer machined the associated output shaft groove (I have reports of at least 3 transmissions from the 1984 model year with grooved shafts but NO circlip, so keep THAT in mind!), located at the nose end. The shaft part number was not changed. The no-circlip change caused a lot of grief to owners. About a decade later the design reverted back to the original reliable version. A fairly substantial number of these 'circlipless' transmissions have failed, some have had catastrophic failures, ripping the transmission to pieces.
is a link to Anton's website, with photos, and some text, on the circlipless
transmission problems...you may find it enlightening!
That is only one of two articles on his website you will find of interest dealing with transmissions.
is Anton's HomePage.
Anton has two articles to look at, not overly clearly shown as two different links, at least not in MY browser at the time I wrote this, so look on the left side. Put your mouse pointer over "transmission" in "Airhead transmissions and circlip problem". The word 'transmission' will be seen to be a link to one article. Click on the word. When finished looking at that article, go back to Anton's HomePage and this time put the mouse pointer over "circlip problem" and click, for the other article.
Many years ago there was not 100% agreement on the exact mode (or reason) for the
failures of later circlipless
transmissions. I have not seen anyone espouse the minority opinion in some years...although they may still exist. But, there were two widely differing basic opinions.
Information here comes from a variety of sources. Information in real
detail first appeared in a 2001 Airheads LIST posting by
Bob Clement of BMW-Montana,
who gave me permission at that time
to post his correspondence with me, which I did the majority of, on that LIST.
In the article you are reading I have added further comments from private communications from several experts in this area, and also my own input. What follows is information from quite a few sources. This article you are now reading, in original shortened form, was submitted & commented upon, & generally approved, by transmission experts. The circlipless information and other information, has since been updated by ME a number of times, and has not been re-submitted, but I believe it to be 100% accurate, and that it would be accepted by ALL the transmission experts. If you have a problem/comment/disagreement, you are INVITED to submit such to the Airheads LIST.
Many private owners have overhauled their own
transmissions, some seemingly quite successfully, some using
information, tools and parts
from Ed Korn or his successor. Most owners will
not want to overhaul a transmission themselves & will entrust it to an expert, as there
are a LOT of real
tricks or specialty knowledge to making a transmission last a long time
and have really smooth operation.
A list of those doing transmission work who know the transmissions well:
Tom Cutter on the East Coast (who does a large quantity of Airhead and other BMW transmissions); Orlando Okleshen, better known as OAK in the Chicago area who may or may not be doing work, but if he does, it is superb; Motorwerks on the West Coast (I can't personally recommend them since I don't know their workmanship myself); Ted Porter (Beemerworks) on the West Coast; Bob Clement who does business as BMWMontana; Matt Parkhouse in Colorado Springs, Colorado; and Bruno's in Canada.
How to determine if you have one of
the possibly troublesome no-circlip transmissions?
This is not so easy, not so cut and dried. A factory bulletin in 1986 gave no specifics on year and transmission serial number. There was no change in part number for the output shaft. THAT is not usual nor unusual for BMW, BMW is known to sometimes make a production part change and to use the same part number. It APPEARS that the transmissions that were affected were shipped with motorcycles of build date beginning near the end of 1984, so that means that some 1984 models may not have the circlip. I have had reported to me ONE 1984 production year circlipless transmission...but that may be faulty, and although requested, I never got the confirming VIN number. TWO other 1984 transmissions with no circlip but with the same already grooved shaft, were reported to me by this same overhauler, who I trust but I never have received confirming details about numbers and dates. Since I often request transmission overhaul information on the Airheads LIST (and maybe the IBMWR list), I refer you to the chart I have later in this article, and you will see the 1984 year status.
There was another, later, factory bulletin, #280, dated 12/08/97, explaining that the circlip (and, therefore the groove) was reinstated, and the SHAFT number was CHANGED. HOWEVER, it appears that the shaft is actually the same as the 5 speed output shafts built from 1974 into 1984. The specified 'new' shaft is 23-21-1-338-793. BMW raised the price of this shaft tremendously. One can, and competent transmission overhaulers DO, modify the non-circlip shaft, but this needs to be done very carefully. The bulletin also mentioned a 'special bearing' for the front of the output shaft. There is some controversy about this, and this bearing was made by a Japanese bearing manufacturer. More later herein.
Transmissions beginning with serial 240765
the circlip re-installed. Confusingly, no
year was specified, but
it appears to be mid or late
1995. Further confusion exists... as
year of production and transmission serial number may well not go
I have obtained information on model year versus transmission
serial numbers, and they are presented later in this article.
It is my belief that you cannot DEPEND on even a 1995 bike as having the circlip, due to an unknown transmission manufacturing date; AND, sometimes later dated transmissions in 1995 did not have the circlip; see my list of reported transmissions, much later in this article. You probably also can not DEPEND on a late 1984 to have, or not have, the circlip. Still, the best information will be had by looking at the transmission serial number. Even THAT is sometimes questionable, if you look at the chart later on this page. However, it seems like 1984 transmissions are likely going to be OK.
Summing up: ...it is possible for a transmission built from PERHAPS LATE 1984, and certainly from 1985, until EVEN AFTER transmission serial number 240765, to not have the circlip and possibly the shaft has or has not a groove for that circlip. We have had reports of transmissions AFTER that # NOT having the groove nor the circlip!!...and at least one is listed below. THUS, BMW's own use, in bulletins, of 240765, is NOT to be relied upon.
How do you find your transmission serial number, and what range of serials can you expect?? Transmission serial numbers are found in one of three places. Early transmissions, from 1974 to 1981 (or, I believe, as late as late 1983, depending on country the motorcycle was shipped to), will have the serial number centered on the top rear center or top front center, where you can not see it without removing the air cleaner, etc. Thereafter, the serial number is located at the top area of the left side, JUST BARELY BELOW where the left airbox outlet hose connects; so you have to squat down to see it. Serials are stamped into the aluminum transmission case. There are some variances, and so noted below.
When reading in this article about 'year', be advised that BMW's 'model year' includes motorcycles that were built towards the end of the prior year, and it is quite possible to see, for instance, even a build date of September, to be included in the following year's model. This is due to BMW policy of closing the plants for the annual month-long holiday (vacation). An October, November, December production almost always will be the NEXT YEAR'S BIKE.
1974: serial numbers ranged from
Y-4300 -> Y20050; after which the numbers continued withOUT
the Y letter. Serial numbers are located at top rear, at center of case.
1975: information sketchy, some end of 1974 transmissions probably used, may have Y prefixes;
otherwise no Y. Numbers from 4225 -> 13500 have been identified, without the Y prefix.
Serial number same place as 1974.
1976: No letter. 5 digit serial numbers. Probably uses serial numbers 25000 through 51000,
some of these may be in 1977 models.
1977: Some from 1976 used, so one can expect serial numbers from 46000 to 63000. Serial
numbers either at top rear center or top front center, in front portion of casting.
1978: 72400 -> 83000, and after those had a prefix letter Z which may have been early 1979
transmissions made in late 1978, as Z-0870 -> Z-0940. Serials are now on the FRONT inside
face of the casting.
1979: All have Z number prefix, from Z-19100 -> Z-36750 (at least).
in 1979 the gusset reinforcements at the bottom of the case were cross hatch like a crossword puzzle. The 1978
had gusset reinforcement running only from front to
rear. Left to right gusset reinforcement of 1979 and later did not exist.
NOTE 2: BMW has had fun and games with transmission serial numbers. It is possible that early transmissions WITH kickstarters had ZSA serials, for one example.
1980: The Z number now begins with a zero: Z-052800 -> Z-064950
From 1981, for awhile at least to 1982, things get a bit confused, with serial numbers LOWER .
1981: There are some numbers that seem to fall in the 1980 group, but the casting is different.
Most will find that the serial number is now on the left exterior side, top rear. Expect serial
numbers of Z-006111 -> Z-029900
Oak has said that some 1981 castings for engines or transmissions had incorrect dimensions, which could cause perpetual failures of the input shaft of the transmission. There is NO fix for that, I think. I personally have NEVER seen this.
In mid or later 1981 (this is unclear to me, although the serial number of the transmission is known, see just below), and some think it happened fully by mid-1982, BMW installed the so-called 'shift kit' inside the transmission. This is a fairly extensive kit with a revised cam shape, modified shifter arm, etc. It is retrofitable, and can be considered for earlier transmissions when overhauled. BMW has a habit of phasing in changes, sometimes on some models long before others....and on occasion one might find a far later serial number withOUT the shift kit change; and transmissions with partial changes. As has been noted well above, the 1984+ transmissions had the transmission serial number on the left outside, just under the air-box fitting surface, just below the air tube to the left carburetor. The earlier transmissions had the serial number at either the rear top, or front top, but you must pull the air-box to see the number. You will do that at the spline service anyway. The serial number for the beginning of the shift kit installation is: 56477 (if one can believe that). The prefix was Z or ZSA. Yes, this information seems to conflict with the charting of transmission numbers here!
1982: Z-036600 -> Z-060400
1983: Z-074700 -> Z-084299
Beginning in very late 1983, or possibly in early 1984, the serial number is located on the left side, just below the aircleaner outlet to the left carburetor.
1984: Z-084339 -> Z-104600
1985: Z-113701 -> Z-130150 Transmissions lower than Z113701 have been reported, such as Z112553 and Z111168.
1986: ZSA-125500 -> Z-125600
Note: BMW seems to be using, at least a fair amount of time, the letters ZSA for kickstart transmissions. More information will be provided to clarify this, in the future, if I can obtain it.
1988: Z letter is dropped (tentative information for exact date this happened). From whatever
time in 1988, serial numbers all now have a 3 letter suffix. Expect numbers from 0147440
AAB -> 0164300AAI. Suffix's may, however, be AAB, AAI, AAJ, ETC.
1989: 0154140 -> 0176330 and suffix (note from snowbum: I am SURE that the serials go higher
in the 0176xxx)
1990: 0180939 and suffix
1991: 0190460 -> 0198650, and suffix
1992: 0207050 -> 0215650, and suffix
1993: 0204190 -> 0230075, and suffix
1994: 0237930 -> 0238660, and suffix
1995: 0236539 -> 0254340, and suffix
Some transmissions, by their serial number, may have been put into motorcycles identified by VIN numbers as from a year out of the irregular sequence, above. Example: your bike is a late mfr'd 1991, and has a transmission serial of 0204xxx plus some 3 character suffix noted in the 1988+ year, above. Transmission use by serial number is quite confusing at times, and is often model specific. Look at 1992 and 1993 above, and then 1995.
After many years, I am still collecting information on Airhead motorcycles that have/had KNOWN circlip-less FIVE SPEED transmissions....THAT MEANS...known BY DISASSEMBLY of the transmission. Information received, after I confirm the VIN, serial number, year, month of production, etc., is posted to this transmission article in this section, withOUT identifying the owners name or the overhauler's name (unless specifically requested I do so by the person informing me...so far, no one).
I wish to know from you or your transmission overhauler:
Transmission...COMPLETE serial number.
Did the output shaft have the circlip?
If no circlip, did the shaft have the groove for it machined into the shaft?
What is the full VIN number of the bike. A VIN number has 17 characters.
There are SOME foreign bikes that do not have VIN numbers, if so, please supply the serial number of the bike (and transmission)
What calendar and/or manufacturing year motorcycle, as best you know?
Most of the time, upon receipt of the information, I will send you a return E-mail, confirming or identifying the month and year of manufacture, perhaps some details on whether it is a USA bike or not, and the bike's BMW vehicle code (which is part of the VIN), and that code is sometimes quite useful when determining which factory wiring diagram, or some other things, goes with your bike.
Reported to ME circlipless transmissions are:
ONE, so far reported: 1984 R80RT....I have never have received the VIN number and thus the bike manufacturing date.
Z016199. Strange number, see my listings, above. Transmission appeared to be original.
It HAD the grooved shaft. NO CIRCLIP.
Well-known transmission overhauler (not sure who that was now) had seen three total like this. Strange, ...as this serial number would appear to be for an earlier bike. It is possible that this was
a transmission that was from 1981, had been serviced earlier
someone, perhaps a dealership; who left it that way. NO information, maybe never.
The bottom line, SO FAR, is
that NO PROVEN 1983 nor 1984 year production has been reported to me that is
missing a circlip.
1985 R80, transmission Z111168, serial 6440490, production 12/1984, no circlip, but shaft had groove.
1985 R80RT, transmission Z112553, VIN WB1046408F6490109, production 01/1985; series code 2472, no circlip, but shaft had the groove.
1985 R80GS, transmission ZSA 11260, serial 6363139, production 02/1985; series code 2471, no circlip, but shaft had the groove.
1985 R80RT, transmission Z113701, VIN WB1046401F6490338, production 2/1985
1985 R80, transmission Z115902, VIN WB104630XF6480439, production 3/1985
1986 R65, transmission Z127619, ECE (Australian model bike). NO circlip, NO groove, production 12/85.
1986 R80GS, transmission ZSA124393, VIN WB1034805G6363255, production 10/85
1986 R65, transmission Z123469, VIN........................6128105, production 9/1985
1986 R80, transmission Z125576, VIN WB1046303G6480655, production 10/1985
1986 R80GS, transmission # unknown, VIN WB1034801G6363284, production 10/1985
1986 R80, transmission Z128362, VIN WB104630XG6480782, production 12/1985
1987 R80RT, transmission Z138188, VIN
WB1046407H6491304, production 10/1986
1987 R80 USA, transmission 0144961AAB, VIN WB1046304H6481119, production 05/1987
1987 R80, transmission 0138910AAB, VIN WB1046301H6481093, production 11/1986
1988 R100GS, transmission 0151096AAI, VIN WB104780XJ6152090, production 11/1987
1988 R100GS, transmission 0155023AAI, VIN WB104780XJ6152610, production 02/1988
1988 R100GS, transmission 0154855AAI, VIN WB1047801J6152611, production 02/1988
1988 R100GS, transmission 0156870AAI, VIN WB1047803J6152688, production 03/1988
1988 R100GS, transmission 0155282AAi, VIN WB1047304J6277710, production 02/1988, NO circlip, NO groove
1988 R80 monolever, transmission 0161951AAB, bike serial number 6448037, production 09/1988
1988 R100RS, USA model, transmission 0154894AAB, VIN WB1046600J6247481, production 02/1988
1988 R100RT, USA model, transmission 0162792AAB, VIN WB1046907K6293354, production 10/1988
1989 R100GS, transmission 0163629AAI, VIN WB1047809K6153197, production 10/1988
1989 R100GS, transmission 0164105AAI, VIN WB1047302K6332169, production 11/1988
1989 R100PD, transmission 0171806AA1, VIN WB1047905L6134016, production 06/1989
1989 R80GS, transmission 0176603AAI, frame serial 6249769, production 11/89. No circlip, NO groove.
1990 R100RT, transmission 0180939AAB, VIN WB1046902L6293473, production 04/1990
1990 R100GSPD, transmission 0174962AA1, VIN WB1047902L6134300, production 09/1989, no circlip, no groove
1991 R100RT, transmission 0185431AAB, VIN WB1046908M6293561, production 08/1990
1991 R100RT, transmission 0191171AAB, VIN WB1046909M6293598, production 01/1991, model code 0469, USA, no circlip, no groove.
1991 R100GS, transmission 01292165AA1, VIN WB1048803M0230223, production 02/1991
1991 R100R, transmission 0204599 AAI, VIN WB1048707N0280111, production 10/1991, actually a 1992 model
1992 R100R, transmission 0204181AAI, VIN WB1048706N0280049, production 10/1991
1992 R100GS, transmission , VIN WB1048803N0230711, production 10/1991
1992 R100GS, transmission 0205604AA1, VIN WB1048800N0230763, production 10/91, USA model, vehicle code 0488, no clip, no groove
1992 (R100GS??), transmission 01213536, VIN ?? 1992??
1992 (??) R100GSPD, transmission 0207039AAI, VIN not available, can't confirm production year w/o it.
1992 R100GS/PD, transmission 0209970AA1, VIN WB1048909N0047487, production 01/1992
1992 R100 (R91)(R100R), transmission 0209230AA1, VIN WB1048709N0280269, production 01/1992, USA model, vehicle code 0487, no clip, no groove.
1993 R100GS, transmission 022756AA1, VIN WB1048801P0231259, production 09/1992
1993 R100GS, transmission 0224420AA1, VIN WB1048804P0231319, production 10/1992
1993 R100GS, transmission 0226691AA1, VIN WB1048304P6467330, production 12/1992
1993 R100GS, transmission 0228652 AAJ, VIN .....646450, production 01/1993
1994 R100R, transmission 023696AA1, VIN WB1048709R0280858, production 01/1994
1994 R100R, transmission 238655AA1
1994 R100GS, transmission 0237931AA1, lug stamped NI
1994 R100GS, transmission 0238984AA1, VIN WB1048805R0231610, production 01/1994
1995 R100R Classic, Euro version (also known as R100-R91), serial 6469362, production 04/1995, with transmission 0249173AAI. Had groove, had circlip, was original, never before opened.
Here is a LATER production, and later serial OF TRANSMISSION, withOUT groove and circlip:
1995 R100 Mystic, transmission 0251758AA1, VIN WB1049706S0400255, production 09/1995, had no groove, no circlip. Because of the production date, I removed my prior comments about possibly only early 1995 models not having the circlip.
More on Testing:
Have the rear wheel slightly off the
ground, transmission in neutral, and rotate the rear wheel slowly.
No notchiness should be felt.
This test can be done with the transmission cold, but is a bit
more revealing if done just after a 10 mile+ ride, so the oil is
hot. This test
tends to also show up a bad
bearing caused by allowing water to get into the transmission,
usually from over-vigorous spraying during
washing (at the hollow
speedometer cable bolt), or from a bad speedometer cable rubber
boot (very common problem, both water
problems can lead to $$$
repairs). This test also tends to show up bad
driveshaft u-joints on the Paralever models, and disconnecting
the U-joint at the transmission output flange, and rotating that
flange, will allow a yes or no on U-joint and
transmission. NOTE!....I highly
recommend making sure
that your speedometer cable boot fits snugly, and is either
internally stuffed with a NON-MELTING grease; or,
BETTER: sealed at the top with silicone RTV; if the top is poor, water can run down into the transmission, causing $$$ damage. Milky (coffee with cream) look to transmission oil is VERY BAD to have happen...it destroys bearings.
For the problem under discussion, the circlip-less transmissions, the most important indication of a SERIOUS problem that you may have is sudden VIBRATION....and possibly noises. If you feel an unusual vibration, and it need NOT be suddenly extreme at all, not even very strong at all, and determine that it is transmission related (pull in the clutch at a stop, engine running....try in gear and also in neutral), that is the time to stop, right then, and have the bike towed. Failure to comply will likely, within a few miles, lead to a massive failure. I CANNOT EMPHASIZE THIS ENOUGH, FAILURE TO STOP RIDING, NOW....NOT 50 MILES LATER AT THE NEAREST DEALERSHIP OR REPAIR SHOP,,,, CAN COST YOU A BUNCH MORE MONEY.
If your transmission is in the range of the circlip-less ones, you might SERIOUSLY consider an overhaul well before you have a failure, as the number of $$ parts to be replaced always greatly increases as you let the transmission accumulate mileage.
Even if you hear and
feel nothing peculiar; every few thousand miles, put the bike on
the center-stand, when the engine
and transmission are thoroughly
warmed up from a ride. With engine off, spin the rear wheel and listen
for growly sounds. Turn the wheel slowly
and feel for notchiness. When the engine and transmission have cooled
overnight, check the drain plug. GENERALLY the
degradation is slow, but sometimes it DOES come on
suddenly....noises and/or vibration.
NOTE: BMW, like most manufacturing companies, is tight-lipped regarding engineering details when it makes a change. BMW tends to be more tight-lipped than many companies, probably from both a corporate policy and the Germanic 'we don't wrongly engineer ANYthing, WE don't have problems....'. BMW, Germany, or North America, may well issue Service Bulletins of various sorts, now and then, but these often do NOT spell out details that one might like to have, and sometimes what is said is confusing, especially considering what is not said. We have to live with that. Sometimes some of us Wrenches manage to get information that is not very public, to say the least. In in some instances I have been given information that is almost to be considered Top Secret. I can NOT divulge in such circumstances my sources... BUT!!.....one way or the other, in almost every instance, I DO manage to get the information needed to you all.
Viewpoints on the circlip 'problem'
#1: This is the much more commonly accepted viewpoint and it is this viewpoint that I personally agree with:
There are three shafts in the transmission, INPUT, INTERMEDIATE, and OUTPUT. The front gear teeth on the output shaft is manufactured on an angle, that is, the gear is HELICAL cut. Its mate must also be that same angle. Picture in your mind such a pair of mating/meshing gears. If power is fed to ONE, then the other has forces such as would move that gear along the axis of the shaft, not just being rotated. This direction of axial force reverses, depending on powering from the engine, or engine braking. In the 5 speed transmission, even in neutral, the forward gear (5th) gear on the output shaft is being pushed forward any time the clutch is engaged, even in neutral, except in the coasting condition. A BOSS on the front of that gear pushes against the rear face of the inside race of the front output shaft bearing. That rear face of the inside race of the front output shaft bearing is the thrust surface for 5th gear. Thus, 5th gear tries to push against the front bearing. Another way to look at this, is that forces try to move the helical 5th gear forward, and move the shaft backwards, the gear then moving on the shaft. Because of this, the front bearing is always damaged, and sometimes the rear bearing, and even the rear cover plate!
There is a tiny amount of end to end float in the shafts fitment in the transmission case (a few thousandths of an inch), established during the shimming process, which ensures that the bearings are not subjected to end-preloading. Ball bearings, used in this transmission at that point, do NOT like preloading, that makes them heat up, and fail.
There ARE some very special types of ball bearings designed for end loading, used in such as the worm drive shaft on electric winches, but this is not pertinent here (and those bearings are VERY pricey).
Prior to the change in what I think was late 1984, there was a hardened snap ring, a CIRCLIP, that fit in a machined groove on that output shaft, it was just forward of the gear, and prevented the bearing from moving forward from that mentioned angled (helical) cut gear pressure. That kept the pressure from eliminating any decrease in the shimmed float.
When the circlip is left out, the first thing that happens is that the axial thrust from 5th gear causes the gear to push the inner race of the output bearing along the shaft towards the front of the transmission, as the shaft, in essence, moves rearward and the gear moves forward on it. If the bearing race moves far enough, it will eliminate any end float. This places an axial load on the bearing, that will cause it to eventually overheat and fail. The large front bearing overheats, begins to self-destruct (the cage which keeps the balls in place starts coming apart and metal goes all over the place). More clearance develops, the output shaft can actually wobble in the bearing. This will, if bad enough, result in the output flange on the transmission (driveshaft U-joint flange) contacting the transmission lip area where the boot is, and the output rear bearing distorts; and, with metal bits already getting into things, all sorts of mechanical mayhem happens, and rather fast. From the first sign of unusual vibration, things deteriorate rather quickly. If allowed to proceed, gears, bearings, shift fork, and even the rear case of the transmission, are ruined.
#2: This is a far less accepted viewpoint, and NOW I am not sure anyone thinks this way:
This point of view is quite different.
I do NOT agree with this. This
view is that while the helical cut gear does move forward under
load, it presses the inner race of the bearing, and it takes that
load because the outer ring is against the gearbox case....and
thus the circlip
is of no matter. Thus if the clip IS
there, the entire shaft moves forward, and the bearing always
takes the axial load, and no force moves
the inner race relative
to the shaft. This point of view is thus that the
smaller bearing should fail first if preload was a
are NO circlips on any of the other
shafts....and, further, the purpose of the circlip was to assist
with disassembly! During the heating of the
transmission, the case should release all bearings, but a
circlip-less large bearing COULD remain in the case when the
shafts are removed,
and it is a bit of work to remove the
bearing...that one, as it is larger, sticks in the case recess...
so the clip was used. These folks agree
the clip removal coincided with the increased bearing
failures....but say that the increased failures are NOT caused by
the clip removal,
it was coincidental with the Paralever
introduction. They say that the GS Paralever
introduction, with its extra travel, puts forward thrust
gearbox, and even an angular thrust due to the changed design
(dual travel angles of the Paralever), and that said angular
taken up by that large 6403 bearing.....and 'proof' is
that no extra large REAR bearing was installed by the
manufacturer. Thus, these folks
EXTERNAL forces are the cause for the gearbox failures, and they
tend to blame too high spring preloads and poor lubrication on
the splines. They feel that BMW put the circlip
method back into production as it was cheap to do, and shows that
BMW 'did something'.
MY explanation: The above #2 viewpoint is faulty. Circlip-less gearboxes on NON-Paralever have certainly failed in this area....negating the above arguments. ALSO, I know of NO failures of any gearboxes in the fashion mentioned in this article that were not fixed permanently by modifying the shaft and installing the circlip (with new bearings, etc....as required). So...I just can't buy their argument; especially when considering the thrust given by helical gears..
Note: It has been reported to me that the stock Paralever driveshaft has exactly the same pivoting length as the swing-arm, assuming the rubber damper is OK, and as long as that is intact, there are no axial forces on the output shaft. Another reason for negating some of argument #2.
NOTE regarding that previously mentioned 'special
6403-C3 bearing' for the front of the output shaft:
It initially, without a very good look, appears similar to any other 6403-C3 bearing, but the front face of the inner race (forward edge of the inner race, the side of the bearing which has writing on it) is cut with a 90° angle (much smaller taper to it than the rear face of the inner race) between the face and the inner hole where the bearing slides over the output shaft instead of the 6403-C3 bearing which has a tapered angle. The forward taper is almost absent. Perhaps this was done to minimize the possibility of bearing creep as the bearing is pushed against the retaining circlip by 5th gear. This modification may well have never been needed. The regular bearing worked fine, never a problem with bearing creep leading to bearing axial overloading....UNTIL BMW started leaving out the bearing retaining clip. This new bearing MAY be the accepted choice....but: The more commonly accepted view is that the elimination of this cheap clip and associated groove caused the problems...AND...I have received word that if one now orders the 'special bearing', you MIGHT get a STANDARD 6404-C3, withOUT the modified inner race face. The 'special bearing' was used only for awhile, and BMW went back to the regular old bearing???
This is all very confusing, so the part needs inspection. However, the 6403.C3 bearing, under part number 23-12-1-338-795 may be received by you with this ID on the bearing: NTN-TM. It will have a sharp edge on the circlip side, so the tiny ring used with it is not needed.
Generally speaking, modifying the shaft,
installing the clip, new bearings, seals, re-shimming, etc., will
be very favorably
priced, compared to just a new shaft from
BMW! Those doing their own overhauls can
have a good machinist cut the
groove to accept the snap
ring. Re-shimming is, of course, necessary with new
Here are some photos:
This is the 5 speed transmission
This is the 'improved' bearing, SAME part number!
note the red line pointing to a circlip. note the TM on the bearing.
Here is an EDITED (by me) query and reply, as was on the Airheads LIST in November 2004, that will explain about one little thing you might otherwise overlook, if you are overhauling your own transmission:
The transmission was a 1983 or 1984 R100RS.
The owner decided to do an overhaul ...it had been done
previously, probably by him,
and the mileage was now around
200,000 km. He noticed a small
"rumble" or notchiness in the output when revolving
the output flange,
the driveshaft shaft disconnected. No
sound, no notchiness when tested from the wheel with the
driveshaft connected. A transmission oil
change (done every
6 months!) showed normal metal powder on the drain plug
Transmission was removed and he slightly released the gearbox cover screws (1-2 turns) and the notchy feeling disappeared totally. Sounds like a preload problem?? The owner then measured the clearance between the output shaft snap ring and the big bearing (6403) inner race; the inner race pushed as far as it goes down the shaft. A 0.25 mm feeler gauge was a bit tight but a 0.20 mm loose. So, he concluded that there must be more than 0.20 mm "undefined" clearance in the shaft and it seemed to him that there is no reasonable way to shim the shaft within 0.1 mm as required especially if the bearing may drift along the shaft. The owner then felt that he would have to shim the snap ring and the bearing inner race to zero clearance.
The owner continued....(my editing here): ""My actual question is about the "bearing drifting along the shaft due to missing snap ring" theory"":
If the front bearing inner race moves along the shaft (despite press fit) ...what... is holding the shaft in place ...that the drift can take place? If it is the smaller bearing then the snap ring push will really prevent big bearing drift but this may cause a situation where the shaft drifts in the smaller bearing, not the big one. Again, a preload will result. He also wanted to know what happens to the bearing outer races in operating temperatures? Do they float ie. are they free to move away from their assembled positions? The operating temperature is not very far from the assembly temperature where the bearings practically can be dropped in their places.
Tom Cutter replied: There are several forces at work that can dislodge the bearing inner race from the shaft. One is the weight and forces of the driveshaft as it undergoes normal rotation, the forces placed upon the output shaft are cyclical, both rotationally and axially. The bearing is designed to be captivated by the clip to preclude ANY axial movement of the bearing race upon the shaft. Unfortunately, the bearing now sold for the output shaft is dimensionally slightly different from the one designed for in the original plan. That bearing had a square corner on the rear face of the inner race, so that it would press evenly upon the circlip. BMW only offered that bearing for a relatively short period, then they substituted a standard 6403 C3 bearing in its place in the parts system. The standard 6403 bearing has a VERY generous radius on the inner bore, which makes the race bear on the very outer edge of the circlip. In some cases the clip becomes dislodged into the adjacent void. The problem is exactly as you have mentioned, and is the cause of the premature failure of so many gearboxes. The cure is to shim the inner race so that there is no possibility that the bearing can be displaced. This can be done with flat shims, although BMW do not offer such, or by simply fitting the round wire expansion ring that BMW used for the purpose. (Emphasis in red by me, Snowbum)
This round wire expansion ring
sits down in the radius of the bearing bore, and effectively
fills the void so
that there is metal-to-metal contact from
bearing to circlip (snap ring). The circlip is:
(size 17 x 1). This is the same circlip
used on the shift shackle in the transmission, in case you get
The round wire expansion ring is 23-21-1-235-006. BMW uses the term Expansion Ring for the wire spacer at the bearing under discussion, and the word circlip or snap ring means the part that goes into the shaft groove.
The output shaft 0.040" (1.01 mm) groove is
0.5 mm deep,
located at 17.00 mm from the step on the forward
end of the shaft
where the 6403 ball bearing sits. Machining should be by
1.00 mm carbide tool. Be sure to
check your shaft, and these
numbers, don't trust ME here that YOUR shaft is the same. The groove must be
VERY precisely located and done so
that the round wire expansion ring, mentioned above, CAN be
inner race of the bearing we
discussing must be installed so it presses (well, touches) on the circlip.
It should not
be installed towards the rear
(maximum space between inner race and circlip).
MY feeling is that
if things are done precisely, then the expansion ring must be installed.
However....I have mixed feelings on that.
UNfortunately, never took any of my own photos when doing the circlip machining
job. However, here is a link to an article with
photos. I agree with the article, for the most part, with
some hesitancy about BMW not using the round wire
at times. The article will show you what the shaft
looks like, the groove being cut, etc.
Here is another
article with photos. Be sure to look at this
http://www.largiader.com/ is Anton's HomePage.
Anton has two articles to look at, not overly clearly shown as two different links, at least not in MY browser. Look on the left side, and find 'transmission, clutch, final drive'. Put your mouse pointer over "transmission" in "Airhead transmissions and circlip problem". The word 'transmission' will be seen to be a link to his article. Click on the word. When finished looking at that article, go back to Anton's HomePage and this time put the mouse pointer over "circlip problem" and click, for the other article.
One thing to really think about is what to do if you think you have a transmission withOUT the circlip. While I am attempting to identify the full range of serial numbers, year, model, etc., that for sure have no circlips, it still remains a bit wishy-washy, although less so as time goes on. You do have a choice on what to do, or not to do.
If you intend to go through the transmission
yourself, you may be opening a can of worms. If you send it out, you really should use one
of our transmission experts, as there is a LOT to know. You
could send it out as a preventative measure. If things come
apart in the transmission, metal will go throughout, and cause a
LOT of damage, typically.
You could also take the attitude that you will watch things carefully, and at the first sign of problems with your OFTEN inspected magnet that is part of the stock drain plug (and, disconnecting driveshaft and rotating the output flange as noted in #5, way above)....you will pull the transmission and have it modified and overhauled. You would also carefully be watching for sudden vibration....and have promised yourself to stop right then....not proceed another few miles....
It is up to YOU!!
***Special note on the throwout
bearing area. This is being put into this transmission article
expanded upon in the CLUTCH article) due to the
potential for someone to think that the transmission
has a problem...which, in
essence, it does, since the throwout bearing is LOCATED in the rear of the
Typically, the clutch will start to slip, when the transmission gets fully warmed from riding.
Some tolerances on some transmissions throwout area bore sizes, and throwout pistons, were not held tightly (well, LOOSE enough). Generally this is thought of as from 1981, when BMW changed the clutch design radically. If the piston fits into the bore a bit too tightly...it may still operate smooth enough, but under some circumstances (temperature, as in HOT!) may stick. Measure the piston, and if it is over about 1.13" (28.7 mm), you MAY want to reduce the outside diameter a bit. I have seen these as large as about 1.142" that still worked OK. I can't give a hard and fast rule here, but if yours is up to 1.141 or so, I would certainly see how it fits, and if a bit too much friction, I would recommend sanding the OD a bit. The pressure on them in operation is rather square, so if any doubt, ....if careful... you can chuck the rather short shaft tip end in a drill press and use some rather fine sandpaper for this. Inspect the bearing, and if it looks bad, replace it. Grease it with a good LIGHT grease (NO moly). The reason to use light grease is that it takes time and miles for the transmission OIL to reach this throw-out bearing. Oil the outside of the piston as you assemble this area. Clean and lubricate the arm and associated parts. BMW has a replacement piston 23-13-1-464-167 which is pricey as it includes the bearing and is a new design, that eliminates the clearance problem of the old style piston...but you do NOT need to purchase it, unless you cannot find a new old-style bearing (if YOUR bearing is NG), or, you don't wish to sand YOUR old piston (if required).
NOTE that the original piston is not a one-piece metal part, rather, it is a part-metal-colored-plastic item, and it expands much faster than even the surrounding aluminum alloy, so common 'feel' for clearances may end up leaving it too tight. The updated part fits directly, no problems.....you measure and decide. I sometimes test the fit with the transmission at operating temperature.
NOTE!!....There is much more extensive
information on the clutch throwout lever, the bearing, etc....be
SURE to see it on this website! clutch.htm
That article has a photo of the later style clutch throwout parts, and the actuating rod, and notes on the FELT on the pre-1981 rods, ETC.
NOTE: The 4 speed
transmission had a good balls-type throwout bearing. The early 5 speed
transmission had a radial needle bearing.
From 1981, BMW BMW went back to the superior
NOTE: The 4 speed transmission and the early 5 speed transmission (pre-1981) clutch push rods had felts located in a groove, and are installed best from the front. The 1981+
transmissions did not use a felt, and had a SEAL instead, and the rod CAN be installed from the rear.
See the NEUTRAL SWITCH article on how to replace a neutral switch on a 5 speed transmission: Neutral Switch replacement.
Replacing the input shaft seal:
This can be relatively easy, or can be difficult. Usually when the seal leaks, the transmission is about ready for an overhaul. Let's assume that is not the case. If the seal leaks, oil from the transmission can flow along the splined input shaft into the clutch, oiling the clutch, and then it will slip. When you have the transmission either out (or backwards some), to do the normal scheduled input spline cleaning and re-greasing, put your #1 eyeball on the transmission input seal. If leaking, remove the transmission to the workbench. It is important to not score/damage the input shaft when removing the seal. You can make a tool to try to remove the seal. HEATING the area with a moderately broad flame of a gas torch will help. If the seal is not going to come out, the next step is to drill quite a few holes into the seal, the holes should be perhaps with a 1/32" drill bit. Drill the holes as close as ou can around at the outer diameter of the seal, but DO NOT drill into the aluminum of the transmission case that is surrounding the seal's outside diameter. I suggest you use a shop vacuum to get all the drilled metal pieces into the vacuum cleaner, not the transmission. Remove the center of the seal and then try to remove the outer part. If this does not work, you will have to remove the front cover of the transmission to press out the seal. Once the seal is out, use a strong solvent and if needed clean up the mounting area very carefully, using fine grit sandpaper if you have to, and use that vacuum cleaner. When replacing the seal, oil or grease it, otherwise you may dislodge the coiled spring in the seal. Use some sort of tool such as a socket or big washer, so the seal goes in squarely.
that excessive end play
of the transmission input shaft can
cause a quite-grabby
clutch operation, and
that can happen cold and/or hot, but more
often when hot. To fix THAT, one must remove and open the
transmission and work on the shaft shimming. One can get an
idea if that is a problem by removing the
it to about the temperature of boiling water, and measuring, with
a dial indicator, the
input shaft end play. Anything over a
few thousandths of an inch is suspect. I'd not want over maybe 0.005".
This problem with
causing a grabby clutch is not overly common, but
it seems to be more so for
the 1979 models. Another
cause is excessive end-play on the crankshaft...rare.....about .007" is the
I personally would allow, and that is for a DRY assembly, which means
you cannot take a measurement that
means much, when oil is in the end parts!
NOTE that excessively worn crankshaft bearings can cause transmission rattle noises.
All the rest of the
The 5 speed transmissions weighed about 24 pounds, without lever and sans oil.
Sometimes I am
asked about the various years of transmissions as to good points,
bad points, etc. A lot of information
is in the
article you are reading. However, the 1974
transmission is a special instance. This was a
transition year for
BMW, from the /5 to the /6, and there were
some things not so nice about the 1974 transmission. 1974
was the first
year for the 5 speed box. The Pawl springs
tended to break. The kickstart parts were SOFT...and use of
is NOT recommended. There were problems in
positively locating the Neutral position, and that wasn't fixed
The 1974 transmissions, in other words, did not
hold up well. Some parts are no longer
available. This parts problem extends
the 17.5 and 15 degree parts area (you might find some parts not
available that are needed to match your 15 degree
parts; so you'd
have to convert to 17.5 degree parts)...... AND, when you
see the parts prices, you will scream. If a
transmission is really bad, YOU REALLY MIGHT WANT TO
CONSIDER A NEW TRANSMISSION; or, preferably, a
really expert rebuilt
one (especially one after 1974)...as the price is less, and the quality will be...or
can be.... BETTER
than a brand-new
one! Quite often, the best thing to do with a really
bad 1974 transmission is to obtain a later model;
those up to
1980 will install with no problems.
1974 and 1981 were not good years for the transmissions. Besides that...in general, the seventies 5 speed transmissions had a habit of breaking the gear dogs off. The gear dogs and associated gears are not the same as later models, parts availability is complicated or just NLA for earlier gearboxes, and this subject can get very involved. You would find one or two dogs broken off and in the drained oil. Cause was the shape of the dog AND the lousy machining, wasn't perfectly at 90 degrees. One dog carried nearly all the load, and broke off, then another might break. Ask about this if confused and you want to know if you can continue riding (a big maybe).
A subject that comes up often is if you can substitute an early and a late transmission (either direction). Here are some basics:
1. You can substitute, directly, a 4 speed and 5 speed transmission (up to the different clutch models that came out in 1980-1981). Problems will be minor for the 4 and early
5 speed substitution.
2. To install an early 5 speed transmission into a 1981 and later bike means a different input shaft on the transmission, re-shimming the transmission, etc. It will work
OK. Note that one way to save money is to simply shorten the input shaft spline length on earlier transmissions, to fit the 1981 and later clutch. See #8, well below.
3. To install a later 5 speed into an earlier bike you need to change the input shaft, or....read on...
4. It is possible to put later components into the earlier 5 speed, and then use it in an earlier bike. That gets complicated, you need the input shaft, the rear cover, shift parts,
input shaft gear, blah blah.
4. The best method, and cheapest, of putting a later (1980/81+) 5 speed transmission into an earlier bike, is to install the later clutch and clutch carrier. That means, in
effect, that from flywheel back, you install all the later parts. Direct fit. I highly recommend you do NOT use the 1981 clutch items, unless they were updated (the 1981
was weak, and could disintegrate)...see my clutch article. CLUTCH.htm
Here's more information on a variety of transmission things:
That article has a number of photos and descriptions that you may find very useful in understanding the 4 and 5 speed transmissions in a few areas, such as the input gear that has the
shock absorber cam ears that sometimes breaks on the early 17.5° transmissions; information on the shifting mechanism and 'shift kit', and some other things. I highly
recommend you review that article....and the links at the bottom. Note that 17.5° gears were supposedly installed from 1982, and I am not at all sure that is totally correct.
CONTRARY to what Anton says about MY article that you are reading, I cover a huge
amount more than just 'historical' data as he put it. I suspect Anton
looked at my article, & did not scan down very far. I get into more depth on things, including
input cam-gear ears, etc. Regarding that input gear: see #3, just a bit below
here...for a more vigorous treatment of the input cam gear and
the 17.5° transmission, ETC.
2. NOTE!!! see article: oiltransfers.htm. The output shaft oil seal on all models except the Paralever, have the open side facing rearward. The Paralever output shaft oil seal open side
faces INward. A new style seal is being used on the Paralevers, install dry, shaped for a couple hours on some sort of mandrel, and then being very careful about the installation, to
avoid the seal being damaged by the speedometer drive. You can use some tape over the drive gear to avoid damaging the seal. If you have an early model of the Paralever, there
may be a goodly sized V-vent at 12 O'Clock in the housing. Block this vent and drill it 1mm. Later models have this already modified. Wet driveshaft models used a green seal.
If you have a non-Paralever model, and oil is transferring from driveshaft to
transmission, you have one or more of: too high driveshaft
oil level; sacked suspension; extreme downhill riding; ....and
may want to fill the 12:00 notch....be sure to leave it with a teeny hole in the
filling. You MUST have a hole. See #4 just below!!
3. The input gear on the 5 speed transmissions has been changed FOUR times, used with THREE different gearsets. The original input gear was 23-21-1-231-519, often just
called the -519 gear. This was used from 1974 to sometime in 1982. The 1979 to 1982 ones have been known to CRACK. Actually, some from a bit later also have cracked. For the
helical, cluster, and 5th gear, BMW changed, for all by mid-1982 or so, from what is often called the Gear Angle, from 15° to 17-1/2°. The fiche may show earlier in 1982. The actual
changed angle is not exactly the part of the gear appearance you might think; rather, it was the tooth profile. Because of this change, the -519 gear also had to be changed. BMW did
so, and still had problems with it...so they did another change, beefing it up. They had to change the input SHAFT too. This occurred in 04/1982, and continued until other changes, in
02/1985. The new shaft for the 17.5° gears was 23-21-2-302-331 for NO kickstarter; and -332 for WITH kickstarter. The shaft was shipped complete, except for rear bearing.
Further explanation: Some 1981 bikes had the first changed 17.5° gear on the input shaft....this was the small shaft, with a COARSE spline. The 1981-2 change was to a FINER spline...and then even later to a larger diameter gear set! The 17.5° input gears, from 04/1982 to 02/1985, might break ears. This is when BMW added splines to the drive dog that mates with the input gear. This change occurred with transmission serial number 115167 on 03/1985 (I think).
Here some of the information is presented a bit
differently, for clarity:
In April of 1982 (from serial 58225 on the transmission??) the helical-cut gears in the transmission were changed from 15° to 17.5°. The new 17.5° gears are identified by a cross or star or X marking on one end. They are NOT interchangeable with the older 15° ones, and only 17.5° matching gearsets can be used. Supposedly BMW also identified these updated transmissions with blue paint dot on the airfilter housing surface of the transmission. However, the later transmissions (1984+) do have serial numbers on the outside, check for yours just barely below the air cleaner box on left OUTside. From 115167 (from April 1985?) the input shaft assembly was redesigned. The earlier gear had a smaller ID, and fit the smaller input shaft OD...with short splines. The reason for the second generation update was because the first generation of the 17.5° input shaft gears (4/82>4/85) were weak and the drive ears might break. These updated parts can be fitted to an earlier gearbox with the 17.5° gears. The original fragile input gear is probably still available from BMW. However, the best thing is to install the complete second generation input shaft assembly. The part is 23-21-2-302-331 if you have no kickstart gear; and 23-21-2-302-332 if you do have the kickstart gear. Supposedly these transmissions are identified by a black painted panel in the ribs in the aircleaner mounting area. Note that in one other respect the input shaft used on the 1981+ models is not the same as the older gearboxes, due to the redesign of the clutch, etc., the earlier ones have a longer nose, see #8 below. Thus there were at least two changes to the input shaft.
MORE! It has become apparent to me that some of you do not understand certain things about the 15 to 17.5 degree change by BMW, maybe you have never had a transmission apart, or maybe, for whatever reason, it is still confusing. I will try to explain it a bit differently here...and add a bit more too. You must be very careful when changing parts to not mix the wrong gears, and this can easily happen with the bevel-cut 5th gear on the output shaft...yes, the one that can have the circlip area problem. You already know that the 17.5° gear has an X mark on it. What may not be clear to you, is that if you need a new intermediate shaft (and have access to the large 20 ton+ type of press needed to disassemble that shaft-set), updating the gear on the intermediate shaft means you MUST change the output shaft bevel gear to the later 17.5° type. .....AND, must change the -519 gear on the input shaft. BTW...BMW does not sell the intermediate shaft except as an assembly and it is very pricey; which is why some use old gearboxes for parts! Early versions of the intermediate shaft are NLA from BMW!
Because of the possibility of you using wrong parts, it is best to inquire on the Airheads LIST if you are at all confused!.........or, let an expert do your transmission job!
4. Only the 1970 & 1971 4 speed transmissions did NOT have the tiny notch for breathing, at the transmission output seal 12:00 position (Paralever boxes
generally have the notch sealed
or a tiny hole). Because of this, the driveshafts on the 1970-1971 bikes tend to have their 'rubber' bellows swell up in hot weather riding. This slight pressurization can
also cause oil transfer problems. An article about this is in the September 1981 BMW News. The only GOOD cure is to add the transmission output vent...which is a drilled hole or a
hand-filed hole. Other forms of venting, even modifying the driveshaft oil plug, etc., do NOT work well (even with a several inch long line run upwards). The shaft housing
could be vented in the more forward area, but the BEST fix, if you have to fix this problem, is to put a vent in the transmission output area, as in later airheads.
5. There are quite a few 'tricks' and adjustments that don't readily appear to someone taking apart a gearbox. For a truly good operating gearbox, you WILL want to consider a specialist.
6A. The 1974 transmissions had a soft kickstart gear on the input shaft, which can cause problems. It is best to not use the kickstarter, except in an emergency. BMW replacement part
will be hardened.
6B. MANY changes were made to the transmissions over the years. Sometimes the serial numbers of the transmissions, or bike serial number, were not
well identified as to
when changes were made. It can get very complicated, one of the reasons I recommend transmission specialists. Some examples here would include the shifter fork
groove on the sliding gears that changed from 6.5 mm to 5.7 mm; square undercut dogs (and associated 'windows') for 3rd, 4th, and 5th gears; the detent spring change
on the selector bracket; the casting was changed for a stronger selector fork shaft, old was 100 mm, new was 105 mm. BMW changed the shifting parts numerous
times. They did NOT incorporate all the changes at the same time. The OFFSET segment for pawl spring clearance was one such change. Several changes occurred at
that same time, with transmission Z5A79720.
.......and there are DOZENS of these sorts of 'nice to know, or NEEDED to know' items.
6C. The /6 kickstarters are not really meant
to be used a lot. The 1974 was weak (see 6A.). NEVER
just jump on the kickstart lever.
Be SURE it is properly
engaged. MY method is to
use light foot pressure, until the lever seems to meet a mechanical stop, then use the clutch lever at the bars to allow the kickstart lever to move downward an additional small
amount. This ensures proper engagement. Release the clutch lever. KICK.
NOTE!! The kickstarter lever on /5
and later will 'bottom' on the footrest rubber. It is
important that it not be a
pure metal contact.....and on the /2 bikes, there is a rubber
bumper. The rubber must be intact.
The 4 speed kickstarter shaft should be modified with a drilled and tapped hole, and use a Loctite-applied (blue) screw and a large washer. Information and a photo are well below in this article.
7. Improved shifting parts, with the external linkage mounted off the footrest, is probably still available as a kit, for the earlier 5 speed transmissions. The design change occurred in 1978.
8. In 1981 BMW made changes in the transmission clutch throwout bearing area, internally as well as the external shift lever arrangement. Also in 1981, BMW made a large change to the
clutch and flywheel, which became a totally different design, and the flywheel is now called a Clutch Carrier....and the transmission input shaft was changed (shorter) to accommodate
those changes. Transmissions before and after that date can be interchanged if the input shaft is the correct one. The input shaft is about 24 mm long on the early
transmissions, and from 1981, it is about 19 mm long. It is also possible to shorten the input shaft on an early transmission, in order to fit it to a later clutch unit...by
simply using a cutoff disc, etc., even with the transmission still together! Be sure to radius the forward edge properly. Within certain guidelines, such as the input shaft
length, and internal gears angle cuts, shift kit or not, proper neutral switch...etc...as all mentioned in this page, most all the transmissions generally interchange.
kit and pawl spring, etc:
Pawl Spring: Inside your transmission is a detent spring, that enables the shifting mechanism to shift gears. If that spring breaks, ....you are stuck in whatever gear you happen to be
in. You MIGHT be able to remove the fuel tank, turn the bike upside down, and then shift into a gear...maybe. I've heard of this, never done it myself. There are 'tools' that will
enable you to change the gear the transmission is stuck in, via the oil filler port. It is tricky, and if you contemplate making or purchasing such a tool, I HIGHLY suggest you look at a
transmission with the cover off, while you manipulate that transmission with your 'tool' to see what twisting and turning is needed. There is an article on this website about these tools:
Emergency-Shifting-Tool.htm Any such tool will be rather difficult to use, without practice.
All the 5 speed transmissions up to the early
1980's could have this pawl spring breakage defect.
This particular spring
is used in all years all transmissions.
WHY the breakage? TWO reasons primarily. The early spring rubs on itself during operation, wearing itself thinner. The spring may wind too tight on the boss, causing excessive
force on the spring. Possibly some faulty springs, possibly a few other things; we just do not know. MUCH MORE on this as this article proceeds.
Pawl spring breakage fixes: One can turn down the boss it rides on by about .060". The boss needs to be around 0.613" or below. If yours is about .630, then machine it down.
The boss size was probably fixed in production, but exactly when is questionable but as I note later, perhaps in 1975 or all before 1976 model year... or so. Tom Cutter posted to the
Airheads list that the original was 15.95-16.0 mm; and the change should be to 15.55-15.6. I don't hold to such tolerances.
Here is my take on the matter:
The post the spring is on has had its diameter changed in the 'shift kits'. You can certainly reduce the diameter of the stock type. The spring must not bind-up in its operation.
Certain of the so-called 'shift-kit' parts, Pawl 23-31-1-242-892; and Segment (offset link) 23-31-1-231-578, supposedly will 'cure' broken pawl spring problems....but modifications
work well. As noted in 6B, above: The OFFSET segment for pawl spring clearance was one of BMW's changes. What has not been said hardly anyplace, except perhaps Anton
Largiader's page, is that the Shift Kit, incorporated by the factory since sometime late in 1981, will keep the pawl engaged, if the spring breaks.
The shift kit uses spring 23-31-1-242-910, and you must use that spring with the shift kit.
In mid or later 1981 (this is unclear to me, although the serial number of the transmission is known, see just below), BMW installed the so-called 'shift kit' inside the transmission. This is a fairly extensive kit with a revised cam shape, modified shifter arm, etc. It is retrofitable, and can be considered for earlier transmissions when overhauled. BMW has a habit of phasing in changes, sometimes on some models long before others....and on occasion one might find a far later serial number withOUT the shift kit change; and transmissions with partial changes. The 1984+ transmissions had the transmission serial number on the left outside, just under the air-box fitting surface, under the air tube to the left carburetor area. The earlier transmissions had the serial number at either the rear top, or front top, but you must pull the air-box to see the number. You will do that at the spline service anyway. The serial number for the beginning of the shift kit installation is: 56477. The prefix was Z or ZSA.
The purpose of the shift kit was to
eliminate false neutrals or hung-up shifting, and improve
shifting in several ways; AND, to improve reliability. The kit is part number
23-31-9-056-150. The kit as such is no longer available, but the parts ARE. Note that the shift kit 'fixes' for the false neutrals does
not have the same level of improvement in the heavy flywheel
models as the later clutch carrier models.
Note as mentioned earlier that numerous parts changes in the shift mechanism occurred over a number of years....such as the offset segments and pawl spring changes.
In the September 2003 issue of BMW Owners News, from
page 34, is an ILLUSTRATED article on replacing a broken
Spring in the transmission. Comments by
me: In illustration 15, the torque obviously should not be
24 foot pounds.....5 to 6 foot pounds is correct. In the
article, the author does not mention that the BOSS needs to be
to be sure the spring does not bind up and break,
again! See above in this long transmission article of mine that you
reading, about that boss and spring.
In the November 2003 issue of BMW Owners News, from page
34, is an article on installing the updated shift kit.
are some errors in this article:
a. In the first column of page 34, second paragraph, the kit does NOT NECESSARILY allow
shifting with a broken spring.
b. On page 34, photo #1 text, it is NOT true that there are no differences. There IS a design
change. The 1974 and 1975 had a reverse neutral....that is....the plate PROTRUDED at
neutral, rather than being DETENTED. The new design makes finding neutral more distinct
and positive. The Neutral switch was changed, and although they look similar, they are
not. The newer plate shaft is changed to insure against clashing with the pawl arm. Photo
#3 text should not really have the second sentence worded like that.
c. On page 35, photo #4 text, it is NOT true that there are no differences. The new arm has an
offset to avoid binding
9B. The "shift kit" is most effective on the
1981 and 1982 models (to maybe
1983, depends on
exactly when BMW
phased in the
shift kit themselves, on the various
because these have the lightened Flywheel, called a Clutch Carrier. The shift kit might improve earlier transmissions slightly, certainly the pawl spring breakage problem
is lessened. The shift kit will help IF the early heavy flywheel has been lightened. The shift kit did NOT come with any instructions.
BE SURE that in your assembly of shift kit parts that the arm is doglegged, that is, off-set.
The shift kit is made up of the following, still
23-31-1-231-578 segment shaft (offset link)
23-31-1-231-611 shifting cam (for 1-2, 5)
23-31-1-451-563 shifting cam (for 3-4)
***The so-called shift-kit parts, Pawl 23-31-1-242-892; and Segment 23-31-1-231-578, supposedly will 'cure' broken pawl spring problems....but modifications to the stock boss
and/or use of the upgraded spring work well for that particular problem.
NOTE, a few paragraphs below, Tom Cutter's comments...and MINE...on how that boss was...or was not...modified by BMW after 1974 or 1975 (We disagree on that point).
For other views, showing these parts lined up and how the neutral switch works with them, see: http://www.largiader.com/tech/airtrans/
That article also has some photos in it that you may find very useful in understanding the 4 and 5 speed transmissions in a few areas.
Use of the shift kit REQUIRES use of the later LONGER neutral switch, or the neutral switch electrical functions will be in reverse of what they should be! The later switch is 61-31-1-243-097, and a spacer 61-31-1-355-262 is used. The 1974-5 neutral switches have a shorter stem. If you install the wrong switch, it does not work correctly, and may be shifting problems!
There are TWO
sections in the ElectricalHints.htm
article on this website on the neutral switches,
starter circuit, and problems. It is complex!
Here is an article on the transmission-mounted neutral switch that has all the details: neutralswitch.htm Please read the entire article, but:
ALL 5 speed neutral switches are CLOSED in neutral, turning on the green neutral lamp (enabling the starter function if the starter button is pressed on 5 speed transmissions). The reason for the shorter and longer neutral switches is that in the early shifting parts, the switch rode on a section of the shifting cam that was a projection, and the switch itself helped make the feel for the 'detent'. On the revised parts, neutral is much more positively felt, by the switch being in a 'valley' of the shifting cam, hence the switch needs to be longer.
NOTE: There is a diode in the
neutral circuit. If that diode shorts, then the lamp is ON if the lever at the bars is
There is also a peculiarity with the 1978-80
models, which have a master cylinder under the fuel tank.
incorporate a float switch, whose purpose is to illuminate
the brake failure light if the fluid runs low. The lamp
gets tested each time you start the bike, via a diode.
the diode shorts, and you are also low on fluid, the
could theoretically energize.
Tom Cutter posted the following to the Airheads
E-mailing LIST in September 2003, and it clearly states what the
kit also does, and I quote
(typos corrected by me)
by me, snowbum, are clearly marked in BOLD RED):
"The kit includes a selector arm that has a second rail which will then will allow shifting, albeit a little sloppy, in the event that the spring fails. (note inserted here by snowbum: I do not believe that to be so, the second arm being designed to prevent overshifts and false neutrals). In my opinion, when the spring is properly installed and the stress relieved, the failures become non-existent. Nonetheless, the new arm is a nice fail-safe piece." (see above note by snowbum, who believes the new arm is not a fail-safe piece as such). Tom later added the following: "The repairs ...referred to are only necessary if one is retaining the older shift pawl. If using the new shift kit, which I highly recommend be fitted at the same time, the parts are upgraded and don't need modification (Or they are supposed to, I found one old shift pawl in a shift kit recently). (Snowbum says: Interesting, if true. The old pawls were gone decades ago, no one else seems to have found wrong parts in the shift kits). I am trying to describe this so it will make some sense, but basically, the spring gets over-stressed when it wraps around the boss on the pawl. The boss can be ground to a smaller OD, and the spring attachment point can be modified by grooving the plate, to prevent the spring coil-binding on the boss. (Snowbum says: The boss was a problem in the 1974, and maybe some 1975 production, and the oversize boss was fixed no later than sometime in 1975. I believe that, from then, the springs break from improper heat treatment, or fatigue, or too soft or too hard, maybe brittle....seems to be a difficult part to
manufacture correctly?). Either or both methods work fine. The important thing is to assemble the shift plate mechanism, then pull the shifter hook arm back as far as it will go, while looking at the pawl spring. If the spring is binding, it will be apparent. This must be corrected." (snowbum says: doesn't happen on 1976 and later, but easy to check).
NOTE: An Airheads LIST inquiry on October 5th, 2011, resulted in Tom Cutter's remarks about the 23-31-1-231-619, the original type of early shift pawl spring, the bent-legged type; replaced by 23-31-1-242-910, with straight legs. Tom noted that you have to use the dog legged shift segment with it, or the spring will bind. Perhaps confusion over this is why Tom and I disagree a bit on the subject?
10. The 4 speed transmission and early 5 speed transmissions can be a devil to find parts for, and to overhaul correctly. I strongly suggest going to one of the experts shown below, in particular Oak, Bob Clement, Ted Porter, Tom Cutter and Matt Parkhouse. In fact, those are my recommendations for any BMW transmission. See near the end of this long article a bit on those folks, and how to contact them.
11. 5 speed transmission gear ratios:
|Stock||Competition/Race. The gear set is 23-21-1-233-427. I have never seen this gearset, and wonder if any were ever sold??|
12. There is an additive that works
modestly well SOMETIMES to smooth the shifting,
particularly with transmissions with
the original older style
shifting parts. Do not use this
synthetic oil. It is Dow Corning M Gear Oil Additive. Comes in quart bottles. Shake well and use up to 2% concentration max, DO NOT USE "UP TO" THE 10% Dow suggests. The
amount to use is about 18 cc for the airhead transmission. This stuff is VERY expensive. DO NOT use with synthetic oil and do NOT add more than 20 cc!!!!
13. The 5 speed transmissions have, on the
input shaft, a cam and spring shock absorbing system, and one of
the gears, that has the cam
on one end, is 23-21-1-231-519.
MUST be replaced if it appears to have worn such that it looks even vaguely questionable; the replacement gear from BMW is hardened. READ the earlier portions of this article
on the complexities of changes to the -519 gear....and the input shaft, etc.
14. There is a plastic roller on a shift lever in the transmission, it is 23-31-1-231-572, and tends, over a long period of time, to start to fail; the steel one from the K models is
23-31-1-451-087, and I have recommended it in the past. I am not so sure about this, now, as I have heard, ONCE, of the steel K bike roller causing wear on its pin...and
against the lever it touches (perhaps there is some heat treatment variation on that lever...or?). NOTE: if the roller fails, the transmission may well exhibit jumping out of gear. This
can also happen if the associated spring breaks. If a question comes up on this point, I defer to the transmission experts mentioned. At least one transmission guru, Ted Porter, is
now using a bearing, #688-RS, for that roller.
15. In 1977 BMW made changes to the
transmission. The slider gears shifting fork grooves
were made narrower, now 5.7 mm,
previously had been 6.5 mm.
The 3rd, 4th, and 5th gears
now had square doglegs (undercut). The detent spring was changed....and it has 5 turns. The cam-plate was changed. The casting was changed for better selector fork shaft
support for 3rd and 4th, and the shaft which had been 100 mm is now 105 mm long.
16. Earlier transmission shift linkage had a foot shift lever connection with a rubber boot over it; the linkage is NOT adjustable other than the foot peg, which is often found at the lowest
position for owners with big boots. Some install adjustable linkage, or, horrors!, grind away the foot peg casting. If you install the adjustable linkage from the ST & G/S models, it bolts
in place of the bent rod. 23-41-2-301-391. Drill the hole in the shift lever, as it is just a bit too small in diameter. Use 1/4" drill. Add the foam donuts 23-41-7-650-149 over each of
the ball joints, or replace your old bad ones. Keep it all oiled.
Transmissions are best overhauled by an expert with a lot of experience. For the person who definitely wants to try doing a transmission, you can do it under tutelage or perhaps get Ed Korn's video, ETC.
Here are some old specifications (there are lots more specifications):
Axial float on all shafts: 0-0.1 mm (0-.004
Gear change lever shaft axial float on 4 speed: as above.
Fork bolts 17 footpounds.
Output flange nut 160 ftlbs (clean and dry on the tapers!...absolutely NO residual oil!).
End cover nuts 6 ftlbs.
The FOUR speed transmission kickstarter idler gear shaft is
press-fitted into the rear transmission cover. There is a tendency,
the gearbox is quite hot from a ride (which expands the
aluminum rear cover much more than the steel shaft!), for the shaft to move
the transmission. Do NOT allow it to
move into the transmission! To do an easy fix is
often best, as the formal fix is removing
the rear output flange,
heating the rear cover, and ...with some experience
knowing what to do next, you remove that rear cover, and modify the shaft.
So, the easy
fix is to do the modification without gearbox rear cover removed; that is, it is
done BEFORE the shaft moves inwards...or worse, the parts inside
fall to the
bottom. The simple fix involves drilling and tapping the shaft, adding a
small bolt and large washer.
In one instance I remember from years ago, the shaft had started to move, and the owner drilled the shaft, added a large flat washer and bolt, and heated the rear cover, and pulled the shaft back into position. I don't recommend it, but it did work OK.
The fix is to drill the center of that shaft at the back of the transmission. Keep your bike metric. Thread the hole, add a large flat washer, larger than the shaft diameter, and use Loctite BLUE on the STEEL screw you will add to hold the washer to that shaft. That prevents the shaft from moving inwards. Use some sort of goop sealant between the washer and shaft/case, to stop any possible oil leakage. This mod has often been done BEFORE there is any or only slight movement, withOUT removing the rear cover. If you have the gearbox rear cover off when doing this modification, then re-assemble the rear cover by first cleaning the shaft and cover mating areas, and then applying a drop or two of Loctite to the shaft and cover as you assemble the rear cover (heated, of course). Some other photos of this job; and, a bit more information, will be found in an article by Matt Parkhouse, in the August 2008 BMW Owners News, on page 38+. If the shaft has started to move, you MIGHT be able to drill the shaft, install screw and washer, and heat the transmission, and pull the shaft into position with the screw. Don't use too small a screw size, and use a decent amount of heat.
4 speed transmission:
Output shaft, drive (rear) end, type 6204C3, 20 x 47 x 14 mm. This WAS part number 07-11-9-981-219,
and that changed to 07-10-1-468-880 Other (front) end, type 6403C3, 17 x 62 x 17 mm. This
WAS part number 07-11-9-981-505, and that changed to 23-12-1-338-795.
Used on both 4 and 5 speed gearboxes. SEE remarks below for 5 speed transmissions!
Layshaft (also called the cluster shaft or intermediate shaft), cover (rear) end, type 6203-C3, 17 x 40 x
12 mm, the part number is 07-11-9-981-214.
Clutch end double row type 3202 in some books, but is 3203C3 (aka 5203), 17 x 14 x 17.5 mm. This
WAS part number 07-11-9-982-409, and that changed to 07-10-1-468-914.
Input shaft, both (front AND rear) are type 6304C3 20 x 52 x 15 mm. Part number 23-12-1-232-695.
Used on both 4 and 5 speed gearboxes.
5 speed transmission:
RE: the 6403-C3
bearing 'where the circlip is' : BE SURE to read the note well up this
article on this bearing, and the associated photo of it.
Output shaft, input (front) end, type 6403 (see 4 speed) (see above too!); and the output (rear) is 6304
(see 4 speed).
Layshaft (Cluster shaft or intermediate shaft), both are 6304.
Input shaft: Uses special bearing #NU204E at the front, and a 6304 at the rear; and note that the
6304THNC3 bearing is used, part number 23-12-1-233-807
In 2005, Matt Parkhouse did a series of articles in BMWMOA-ON, on overhauling the 5 speed transmission. GOOD stuff.
Anton's transmission article. Highly recommended:
Listing of parts, some photos, including of the shift kit items, ETC. Site will further your education on the 4 and 5 speed transmissions. Anton also lists some of the many changes BMW made to these transmissions over the years, what can & cannot substitute & what won't fit, etc.
Here is a website page that tells you how to overhaul your 5 speed transmission
yourself. Whilst there are
plenty of tricks, etc., that are not in this
article, it SEEMS to be complete enough that YOU may be able
to do an overhaul.
This link was given to me, and I have NOT gone over the instructions step by
I have also been informed that the nylon roller that someplace in
the article is mentioned as being
replaceable by a metal one (maybe he means the
K bike metal roller??)....has a wrong part, and the part
should be 688, not 628,
both being 8 x 18 x 5 mm.
However, see my much earlier information on that....at item #14, above
SI-00-053-88-new-style-seals.pdf is a file on this website that describes the 'new style' Teflon seal used at the engine output and at the transmission output. READ IT!
Preloading the Shift Lever, what it does to make the transmission shift smoothly!
I will try to simplify this....well, somewhat. Taking a bit of license here too on the explanations.
Lightly preloading the shift lever can and does work on many motorcycles, and it works on the Airheads and the Classic K bikes. They are not the only vehicles where this works nicely. PART of the good-effect is due to helping to slow the moving parts just a tiny wee amount during the actual shifting attempt, to help line-up the various parts.
For the Airheads, the transmissions, like most motorcycle transmissions, use dogs on the end (sides, internal and/or external) of some gears. When shifting, you are moving gears out of mesh or trying to put them into mesh at the gear's teeth, but you are also sliding some gears along shafts (typically the gear is sliding on a splined section) and the side of a gear is try to mesh with the side of another gear, by means of those side dogs; sometimes both are male types, sometimes there are male and female dogs (that is, the female ones are depressed inside the end of a gear). Thus there are two types of meshing going on, one is the normal gear teeth type of meshing, and the other is the sliding dogs. End dogs are simply square sections on the sides of gears. When two such dog sections mesh with each other, the gears are, more or less, locked to each other. A good cutaway of a transmission or a good sketch will show this nicely.
Here is a really good website that shows how these types of transmissions shift, animated, and also very good single photo of a gear dog end, ETC.
Highly recommended: http://www.gadgetjq.com/transmission.htm
As you try to shift your 4 or 5 speed Airhead transmission, numerous things must happen at the same or approximately the same time. Some parts must speed up, some parts must reduce speed, in order to enable a meshing (of dogs and gear teeth). Gearbox manufacturer's have engineers that get headaches from trying to get gearboxes to shift smoothly, compounded by the fact that motorcycle transmissions do not have synchronizers. For motorcycles, all sorts of friction effects from gears and shafts moving, together with oil viscosity, etc., are involved. This is a DEEP subject, and one that BMW and its transmission designer-maker (Getrag) have faced, with some strange results now and then ...like adding friction producing O-rings on shafts. BMW transmissions, properly put together, shift nicely, but other things can work against smooth shifting....AT TIMES. One of those things is the heavy early model flywheels, as the engine does not like to slow down as quickly between shifts, as does the later lighter clutch/flywheel models (1981+ with the new-style clutch carrier). Even the 1981+ lighter clutch carrier assembly is heavy and has a lot of INTERTIA, compared to most multi-plate type clutches used on, for example, Japanese and British (and American) motorcycles. Thus, slowing the engine for shifting takes a small amount of extra time, but that is very noticeable to YOU, the rider. A lot of things must happen in a tiny fraction of a second.
Aside note: in SOME types of racing, particularly drag racing, decades ago, fast shifts were considered a must. Methods included removing some of the dogs, increasing clearances where the dogs meshed.....and an "momentary ignition cutout switch" was installed and was enough to allow the heavily loaded gears to DEmesh and remesh (constant foot pressure on gearshift lever). In fact, many a drag bike rider did not use a clutch!....the shift lever was heavily preloaded, the switch literally "hit" and the bike shifted.
You CAN up-shift your Airhead between gears by preloading the shift lever and using the throttle....and no clutch.......but I recommend NOT doing this. If you practice, it is not hard on the transmission once you learn to do it correctly.
If the gears/dogs do not line up rather closely at the exact instant you want to shift, then it can take some additional rider effort to get the parts to mesh quickly. Normally, coming to a stop sign, Airhead riders raise the rpm and shift downwards to first gear BEFORE quite coming to a complete stop. Otherwise, you may have to slightly engage the clutch or double clutch, play with rpm, etc. when you want to shift from Neutral to first gear when starting off. In shifting downwards it is normal to blip the throttle slightly. Experienced riders can often shift downwards without the loud clunk often heard from Airhead transmissions. Upward shifting is usually easier, although the 1st-2nd transition is a bit longer and longer-taking. BMW transmissions tend to take a lot of miles to fully break-in. The transmissions can also shift differently, give a different 'feel' if the oil is changed to a different viscosity grade, and, occasionally, just the brand/model of oil has made a difference. A Dow additive, in a weak amount, is sometimes tried for balky shifting....sometimes it helps.
Note: it is entirely possible for two gears to try to mesh but the teeth (or dogs) are directly opposite each other, that is, it is square end of one tooth or dog against same on the other. Unless you can get one of the two gears to move SLIGHTLY, you will not get meshing. It is not unusual for this to happen; and it can happen at the side dogs teeth, or the outer teeth of the gears.
Side note: On kickstarter Airhead models, particularly early ones, if you push the kickstarter down and it seems locked (unless you use a LOT of foot pressure), I suggest you pull-in the clutch lever at the bars, and move the kickstarter lever downwards a bit (easy) and then release the clutch. That allows proper meshing; due to how the gear setup is. It also greatly reduces the strain on the parts from otherwise very excessive foot pressure on the kickstarter lever........all of which is torque-multiplied by the mechanical leverage, and applied to, perhaps, not overly strong innards.
Bottom line: Pre-loading helps improve the friction, etc., to allow closer rpm matching of the internal parts, and thereby easier shifting.
DYI (Doing It Yourself) (part 1)
****If you insist on overhauling your own 5 speed transmission, please understand that there are a lot of little things to know. However, many HAVE done an overhaul successfully; and whilst the overhaul might not be up to 'Guru' standards, it can be perfectly adequate. I have greatly resisted pressure to do step by step transmission overhaul articles, because of all the little details, which vary by year of transmission. On the other hand, I do wish to have something for you to look at. So, I offer the following URL: http://jhau.maliwi.de/mot/gearbox.htm
READ this entire article of mine all the way through, then go back and read that just-above URL.
After having read my long article you are presently reading, studied it, and are still thinking about doing it yourself, then, go back and read the just above linked-site; and this time click on all the various links, particularly at the bottom, then decide if you want to proceed. That article does not have all the finer details, many of which are in MY article, above.
Bottom line: If you are the methodical and careful type of person, YOU PROBABLY CAN overhaul your own gearbox (and, if you need some press or machining work, that is easily farmed-out).
Tools and video
for transmission work, and other work used to be available from
Ed Korn who previously did business as
Cycleworks, Inc. in town of Oregon, WI.
Ed did some
work, had LOTS of tools
(and some parts) for everything from the Isetta cars,
through the /2 era, up until the Airheads stopped
in the late 90's. He had a rather extensive line of tools,
some VERY cleverly designed, and he had instructions, videos, all
sorts of stuff. Doing a run-through of his
website was informative to many folks. Ed sold the business
to Cycle Works LLC, located at
5805 Haskins Street, Shawnee, KS, 66216 (913) 871-6740. Contact the new owner at: Dan@cycleworks.net ((NOT .com!!)).
The URL address is still www.cycleworks.net .............Dan will likely be very helpful.
DYI (Doing It Yourself)
This section was posted by Tom Cutter to the Airheads LIST on June 10th, 2012; in response to some questions, and I leave THEM intact too.
I have NOT edited all this, except for paragraph separations added and a couple of miss-spellings.
My purpose in putting this posting here is to give you a feel for what is done.
""When I do a gearbox job, I heat the box in the oven to 225F,
the shafts by hand, shift the gears up and down, and
input and output shafts
to check for grossly excessive
I strip the whole gearbox down to the last component, throw
into the parts washer, turn on the air agitator
and go pull
parts, write the part numbers on the customer bill and on
list, then come back to the clean parts. I rinse the parts,
shaft, wire wheel the gasket surfaces, and lay it
all on the
long table for individual component inspection. That is the
time-consuming part, because each part
evaluated for either the "SAVE" or "REPLACE" pile.
I replace all the seals and bearings, so I don't waste any time inspecting those. I clean and sort the shims, and put them into my shim assortment based on size. A this point, all inspection decisions are made, all replacement parts are accumulated and laid out in assembly order, and I'm ready for clean final assembly.
Reassembly takes a very short time, usually less than10 minutes. I first install all the new seals, then stick the gearbox housing in the oven at 275F for 25 minutes. That gives me enough time to replace all the bearings on the shafts, assemble the output shaft and install the little end input seal in the 81-on models. By that time the housing is fully heated, I pull it from the oven, immediately install in this order: Input roller bearing outer race with cage, oil baffles in the cluster and output shaft recesses, the 3-4 shift fork on the stub shaft. Then I engage the cluster gear onto the shift fork, swing it out of the way and lower the output shaft into place. Swing the cluster shaft into engagement with the output shaft and drop both into the bearing bores. Then I engage the two shift forks onto the output shaft, lubricate and slip the shift shaft into the forks and the housing bore.
The shift camplate assembly goes in next. I use my gloved hand to reach down and lift each shift fork into engagement to the selector plates. While the case is still piping hot, the selector assembly retaining bolts are installed from the outside of the case and torqued.
Now it sits to cool down to room temperature. While the parts are cooling off, I complete the repair order paperwork, call or email the client, get a coffee then pull out the measuring tool set for shimming. I sit down to the now-cool gearbox and take all of the shaft and bearing bore measurements, which I record on a small pad of graph paper. (I could use a custom-made form for shimming calculations, but I've been using these little pads for 40 years, and the collection of many hundreds of calculation sheets is kind of satisfying.) This is another "look and think" time. I expect the clearances to measure within a very narrow range. If they do not, I know that there is an anomaly of some kind, possibly a stuck shaft, and assembly error or a flawed replacement part.
Once I am satisfied that all of my measurements are correct, I select the correct shims to get my favorite clearance, and I stick the shims into the cover bores with a dollop of grease. I clean the output shaft taper with some tri-chlor solvent, visually inspect the inside of the gearbox and say good-bye to all those gears, confident that I will never see them again. I set the cover in place on the top of the shafts, and heat using two MAPP-gas torches unto the cover falls into place, assisted with a couple light taps to align everything. Before the cover cools, I install and tighten the nine cover bolts, turn the gearbox over and give a couple light taps on the exposed input shaft. (That seats the bearing in the hot cover better.)
When the cover has fully cooled off, I install the neutral switch and test it for continuity, I run the shifter through all the gears, install the drain plug with a new gasket and the fill plug is lightly screwed on with a large bold tag that says "ADD OIL!" along with recommendations for oil type and quantity for the particular gearbox. I install and grease the clutch throwout bearing and piston assembly, the clutch pushrod and actuating lever assembly. Everything gets wrapped in a clean plastic bag, swaddled in protective bubble wrap and returned to the customer's shipping container to await completion of payment arrangements prior to shipment, or for customer pickup."
<<I'm wondering if maybe you, Oak, and 'Snowbum think we shouldn't have gone to 'Cuda's transmission school, but it was really fantastic.>>
"I have no idea what Oak or Snowbum think. I know that I think it is great that Joe and other guys like him are dedicated to accumulating this knowledge, sharing it and carrying it into the future. That is the only way the knowledge base will continue to grow and survive. It is inevitable that some mistakes in information transmittal will occur, but that does not invalidate the process. Learning is a living, breathing process."
<<I learned so much. I also learned that like you said, this kind of work is WAY over my pay grade. >>
"And it is those guys who learn that who will seek out the assistance of paid professionals. There are plenty of those to go around."
Snowbum snipped some things here, as not pertinent.
Tom closed with this:
"(One thing I ask of all of you: This post is not intended as an instruction set on transmission rebuilding. Please don't post questions (on list or privately) asking for explanations of each specific detail. I simply do not have time for it. )"
The following are all known by me and recommended by me for ANY type of Airhead work:
"Oak" (Oak Okleshen). I can recommend OAK for ANY type of airhead work. Real craftsmanship, and very knowledgeable. Perhaps THE most knowledgeable and METICULOUS craftsman on Airheads in the USA. Official Friend of the Marque. MY mentor! Be SURE to ask about how long your job may take.....he may be backlogged or no longer working.
22637 S. Ridgeway; Richton Park, IL 60471 firstname.lastname@example.org
Anton Largiader in Charlottesville, Virginia email@example.com Virginia Motorrad www.largiader.com Take a look at: http://www.largiader.com/tech/airtrans/
That article has some photos in it that you may find very useful in understanding the 4 and 5 speed transmissions in a few areas. Anton has two articles to look at, not overly clearly shown as two different links, at least not in MY browser: Look on the left side, and find 'transmission, clutch, final drive'. Put your mouse pointer over "transmission" in "Airhead transmissions and circlip problem". The word 'transmission' will be seen to be a link to his article. Click on the word.
When finished looking at that article, go back to Anton's HomePage and this time put the mouse pointer over "circlip problem" and click, for the other article.
Ted Porter's BeemerShop, on the West Coast. Ted has a deservedly solid reputation, and was with BMW for a long time. Very knowledgeable. Quality work. His shop has a good reputation. www.beemershop.com 34 Janis Way Ste E, Scotts Valley, California (831) 438-1100
often just referred to as BMW-Montana; Bob has been working with Airheads
91 Blanchard Butte Rd.
Roberts, MT 59070 406-445-2044 firstname.lastname@example.org
Tom Cutter's Rubber Chicken Racing Garage.
Tom has been working on BMW bikes for decades.
1360 Colony Way
Yardley, PA 19067
cell: 215-206-9787 email@example.com
Matt Parkhouse in Colorado Springs firstname.lastname@example.org or email@example.com Matt Parkhouse may have some excellent used transmissions.
The following are known to me only by hearsay:
Charlie Johnson BMW Motorcycle Service (all models) 18145 Hummingbird Road Wayzata, Minnesota (952) 449-0357
Wuma, Inc (Guenther Wuest) firstname.lastname@example.org
6891 W. US Hy 150
Fredericksburg, IN 47120,
He ALSO does conversions to the 5 speed transmissions; information on this conversion will be found in the SidecarURL.htm page on this
website. Motorren Israel also does different type of reverse gear conversions.
Motor Works, Inc. 1490 Island Ave. San Diego, CA 92101 619-233-8875 email@example.com
Brunos, in Canada, has a very good reputation.
No personal knowledge, but I think he is trustworthy and competent from what I
Revisions: (transmission ID and VIN updates are not listed)
07/07/2008: all prior updates incorporated,
and, minor editing for clarity; and include groove depth; add
hyperlink to Anton's site
08/29/2008: Re-arrange order of some items, change some emphasis, explain a few things more clearly.
10/01/2008: Relatively major revisions. Few if any specific technical parts descriptions & details were
changed, but wording & emphasis was changed in numerous areas, & information on the
more accepted type of circlip caused problems was expanded-upon, primarily as the result
of someone contacting me who gave input on things that were not clear enough, or really
required better explanations.
12/17/2008: Add photo and description of 4-speed kickstarter idler gear shaft modification
01/17/2009: Add reference (2) in the addendum section
08/06/2009: Some modest updates for clarity, and some URL references recommendations, particularly
for the 1974 year.
08/09/2009: Updated information in several places, including item #14.
10/10/2009: Go through entire article, and try to clarify as many details as I could
11/01/2009: update URL's and recommended repair specialist list
12/27/2010: minor update for 1995 models.
01/28/2011: Clean up repetitive stuff...somewhat
02/03/2011: Add 16
06/13/2011: Add more links
08/01/2011: Add section on preloading & smooth shifting and theory behind it; fix Cycleworks information
08/04/2011: Re-arrange article a bit, edit out some superfluous repetition stuff
10/05/2011: a bit of additional commentary about the shift pawl springs
12/24/2011: add two hyperlinks
04/28/2012: Begin revising article for clarity, particularly the pawl spring & shift kit information, which had
been scattered in the article.
06/10/2012: Add DIY part 2
06/17/2012: Update information on serial numbers and years, and add comments
07/15/2012: Change this article from 59 to 59A. Split #9 into 3 sections, add link to a new article of mine
which is 59B.
10/15/2012: Add QR code, add language button (deleted in 2013 due to problems), update Google Ad-Sense code
11/15.2012: Re-arrange article. Clarifications. Better section divisions. Make width shorter, so might
display better on smaller screens. Fix many html closing tags.
12/13/2012: Fix poor choice of wording for the description of the two types of throwout bearings,
when installed, etc. Original wording could be misinterpreted.
01/03/2013: Add photos of 6404C3 special bearing, late type, and the 5 speed gears/shafts
03/30/2013: Add a bit more information to Transmission Problems, Checks, and Testing.
05/04/2013: Add transmission rattling noises section, near top of this article.
06/21/2013: Add hyperlink #3, minor other changes.
07/26/2013: Add more on substitutions.
11/18/2013: Minor changes for clarity & transmission reporting, including wording & an internal hyperlink for ease
in readers jumping to another area in this article.
04/07/2014: Major changes, but strictly for clarity and eliminating some redundancies.
© Copyright, 2014, R. Fleischer
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