BMW AIRHEADS: 4 & 5 speed transmissions
Oil types for your transmission. Noises. Rattles.
Output shaft snap ring (circlip) & groove.
Serial numbers versus model year. Pawl spring breakage.
Neutral switches. Shift kits. Input shaft seal. Kickstarter.
Shift linkage. Throw-out bearings & pushrod. Bearings.
Shifting smoothly--preloading the shift lever and why.
Gear ratios. Doing It Yourself .....etc.
http://bmwmotorcycletech.info/transmission.htm Many folks have problems understanding, let alone visualizing, how BMW transmissions operate. I am putting 5 links at the beginning of this article to help with understanding.
Preliminary & Introduction:
Link #1: From the BMW Factory School on the 5 speed gearbox and both early and late clutches.
www.gadgetjq.com/transmission.htm An Airhead shifts similarly except that the shift levers are moved by a flat plate cam.
Many folks have problems understanding, let alone visualizing, how BMW transmissions operate. I am putting 5 links at the beginning of this article to help with understanding.
Link #3: This shows a BMW GS transmission. Review this for shifting & various noises, etc.
http://w6rec.com/ Some information how a transmission works; /2 transmissions, testing, details. Some information not covered in my own transmission article, below, that you are reading. 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, & you will find the the exact part numbers & information in my own
http://bmwmotorcycletech.info/clutch.htm article for your Airhead. See also my item #14 (below) on the roller. Duane's article does not cover a LOT of what I do & certainly does not cover all my testing, nor how to go about any ideas of overhauling a transmission, shimming it, nor ANYthing about the 17.5° gear angle change, etc. My article is VASTLY more complete, particularly about 5 speed transmission problems.
Link #5: http://jhau.maliwi.de/mot/gearbox.html
OIL:BMW has never waivered in its transmission oil recommendations, and this includes the last Airheads. While straight grades are listed in the Owner's Handbook, the only listed multigrade oil is 80W90. BMW did not restrict use of petroleum and synthetic oils, stating only to use a GL5 oil, & that it be a Brand Name (BMW-speak for "quality").
In the past I recommended you use ONLY a quality petroleum GL5 oil in your Airhead transmission; preferably in grade 80W90 for most conditions. I also said that you could use 75W90, 80W90, or 85W90, depending on weather. There are oils available that replace the "90" with 120 or even 145. 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 (that also means the un-started engine temperature generally), and that you will be riding fast &/or with heavy loading, or pulling a sidecar or trailer ....all in very hot weather ... that means consistently 100°F or more. There is an exception; some transmissions will stiffen-up gear changing when the oil is hot. While there can be other causes that a change to a thicker oil will not help, in this instance you CAN try the thicker oil, such as 85W140 or similar.
My present recommendation is that, if you want to, you may use a synthetic gear oil of good quality. There is no question in my mind, that HIGH QUALITY SYNTHETIC GL5-rated oils will, or can, PROLONG the life of your transmission (& rear drive). That does not mean that they should always be used. Ithink they are now good enough for me to recommend them in general instead of dino oils. In some instances seals & the synthetic oils may not be perfectly compatible. If you change from a dino to a synthetic, & get some weeping or leaks, change to another type of synthetic, or go back to a dino. With the change back to dino oil, the seal(s) are then likely to reshape with some miles & time and stop weeping. Seals have varied in materials over the years, with the same part number. I recommend that you NOT use any additive if your transmission is filled with synthetic oil. One such additive is made by Dow Corning and sold, $$$$, by bearing sales companies. I do not recommend ANY additives except in very special circumstances. For a synthetic oil, I am presently recommending only Spectro brand gear oil, in 75W90 in the version version called "Platinum", for the transmission & the rear drive of Airheads & Classic K bikes. I have no objection to it being used in the driveshaft (of those models using oil there). In fairness, I will also note here that one experienced transmission rebuilder, Tom Cutter, my words here, believes synthetic gear oil in your Airhead is not good, leading to unspecified WEAR.
I also have NO objection to Castrol 80W90 GL5 oil in NON-synthetic; NOR do I have any objection to any of Spectro's GL5 rated gear oils, in appropriate SAE viscosities.
Any oil will thin & thicken with temperature changes on 'its own chart curve'. How this happens is a property of the base oils & additives. Using a thicker (higher viscosity) PETROLEUM oil (than the stock 80, 90, or 80W90) ending in 120 or 140 or 145, will take the transmission operation out of the design operating area, as far as gears & parts speeding up & slowing down during shifting due to oil friction, etc, thus gear changing up & down can be different, and may give problems. Restating this: One difference is in spin up & spin down time for shifting. Gear clashing can be different. I am also concerned that, when colder than approximately 90°F (or maybe somewhat more) air temperature; and/or the engine not being used at high output (which produces more heat, that DOES get to the transmission), lubrication is possibly reduced, protection could be decreased, & there are other not-so-nice things. For example, using 80W145: The oil at any normal operating temperature will ALWAYS be thicker than if the oil was any lighter grade, including 80W90. If you wish to think about this in a different way, imagine the oil is rated at 80W20000, & THINK about what that means. Thus, at most any temperature you will be riding at, even after a full warm-up, the oil is thicker, a lot thicker. NOTE ALSO that the thicker oil will have more horsepower losses associated with it ....more friction within the moving oil itself too ....besides the various gears, etc., changing shifting characteristics due to different slow-down and speed-up slowing.
There is a rating called Viscosity Index (VI or v.i.), which is the RATE of thickness 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. For such as a 80W145, as just one example of oils with a much higher top number; as your parts & oil rise in temperature, the oil thins less, & the specific lubrication qualities of friction inherent in thicker oils, is modified ...AND note what I mentioned about speed of parts slowing-down or speeding-up being changed from AS DESIGNED. The base stock & the additives control this. BMW wants you to use what it specifies. That's generally a very good idea. BMW's transmission designer/manufacturer, Getrag, specifically designed the transmission to use either straight 80, straight 90, or 80W90 multigrade, all in only GL5. Just in case you were 'guessing' here ...no, the objective is NOT super high viscosity index. Spacing of parts, spin-down and spin-up times, etc., all change as the transmission heats up; and the oil grade is specified to help match other transmission characteristics.NOTE: Better oils ARE now available, compared to when your bike was made, but 80W90 quality oils rated GL5 are still excellent, although I might add 75W90 being slightly better, especially for those who ride (or start their rides) in COLD temperatures.
Any oil needs to be of a type that leaves a very thin layer that sticks to the gears & bearings rather than drip completely away during overnight or longer storage. This is particularly so for the 5 speed transmission. You will not be able to easily find out about YOUR PROPOSED OIL, in this regards. This is another reason to use a QUALITY oil.
I believe the transmission & rear drive oil should be changed every 10,000 miles; with the synthetics going towards 20,000. I believe it will pay you over the long run to use MY recommended oil change intervals. I would rather see you use a petroleum oil, 80W90 or 75W90, GL5, and change it every 10,000 miles, than have you use a synthetic and change it at twice (or more) miles.
HINT: Yearly, remove the band clamp on the rubber bellows at the Universal Joint area at the back of the transmission. With the rear wheel locked (via brake with a helper, or other method....), use fingers (or?) and push back a bit of the forward part of the rubber bellows, and check the tightness (DO NOT loosen first) of the 4 screws at the U-Joint. I usually have the transmission in gear, & use the clutch lever to enable rotating the flange to the 4 positions that will be needed (rear wheel is off the ground). Your method can vary. Use the proper adaptor tool, on your torque wrench, and check the 4 special bolts at 26 footpounds, said torque to be at the bolt itself, so use the torque wrench adaptor at 90 degrees, or, if the adaptor is used straight out, adjust the torque wrench lower, as calculated, to enable the proper 26 ftlbs. If there are lockwashers under the 4 bolts, remove, and obtain the proper slightly shorter bolts, do NOT install lockwashers or washers of any type. Install with clean and dry threads, one drop of medium strength (blue) Loctite, and tighten to 25 to 26 ftlbs. When checking torque in the futue, always check tightness, do NOT loosen first.
Transmission rattling noises (oil hot, idle rpm, transmission in neutral, clutch lever forward---not pulled, and bike is stationary):
The cam that operates the valves is a jerky load on the timing chain...that can cause irregular power pulses, primarily but not exclusively from irregular ignition timing. A bent cam tip, as on pre-1979 models, even as little as 0.001", can cause irregular ignition timing & 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 & also 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 models prior to 1970, it was common for folks to brag about how smooth & silent their engine was at idle. UNfortunately, trying to idle the engine so low (many would try for 500 or 600 rpm, let alone 800), is quite BAD for the engine; particularly a worn engine. I suggest 900-1025 rpm for all models from 1970.
If the idle RPM is too slow, oiling to the chain & sprockets will likely be low enough to accelerate wear on those items. This is worse with an older worn engine. The only oil these parts get on an Airhead is from the hole in the oil pressure regulator. If the oil is hot & thin & idle rpm is low, then oil pressure is low, & there is no or much less oiling.
Airhead rattle is LESS likely and less noisy, on models from 1979 due to the improved ignition stability (cam drive to the ignition is much improved), and slightly better from 1981, and the somewhat better chain tautness control; at least early-on, but DOES deteriorate with increasing miles.
Transmission problems, checks, testing:Drain the transmission oil after a ride, when the oil is warm to moderately hot. Put #1 eyeball on the magnetic drain plug. If there is anything more than a modest amount of soft fuzz felt between your fingers, then there is a problem. NO SHARP PARTICLES NOR PIECES should be felt. If there is anything small & 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.
If you have a sudden vibration while riding, and possibly noises (or not), and the vibration ceases when the clutch is pulled in while riding (and throttle turned off), and you can also try in gear, and in neutral, and you maybe also find noise or vibration with the clutch NOT pulled in, ......
A link to a 5-1/2 minute video by Ted Porter. http://Beemershop.com. Many folks comprehend better with visual presentations; after which they are ready for the in-depth explanation.
http://largiader.com/articles/circlip/ is one of two transmission articles on Anton Largiader's website that you will find of interest.
http://largiader.com/ is the HomePage. Anton has two articles to look at, possibly not overly clearly shown as being two different links, so look on the left side list of articles. Put mousepointer over "transmission" in "Airhead transmissions and circlip problem". The word 'transmission' will then 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 again 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 & reason for the failures of circlip-less transmissions. I have not seen anyone espouse the main minority opinion for some time now. I DO HAVE the two basic opinions later in the below article. AFAIK, the circlip information first appeared relatively widespread in a 2001 Airheads LIST posting by Bob Clement of BMW-Montana, who gave me permission then to post his correspondence with me, which I did the majority of, on that LIST. In the below article I have added comments from private communications from several transmission experts, & you also get my own verbose input. ...and, as noted, the two different ideas & opinions about the circlips is included.|
This is not so easy, not so cut & dried; there ISN'T any absolutely perfect method of determination for the earliest transmissions without taking them apart! A factory bulletin in 1986 gave no specifics on year & transmission serial number. There was no change in part number for the output shaft. BMW is known to sometimes make a production part change and to use the same part number. It APPEARS that the earliest transmissions that were affected were shipped with motorcycles of build date near the end of 1984, so that means that some late 1984 models may not have the circlip. Since I often have requested transmission overhaul information on the Airheads LIST, ETC., I refer you to the chart I have later in this article; you will see the 1984 year status. Take a look at the 1994-1995 information too!There was another, later, factory bulletin, #280, dated 12/08/97, explaining that the circlip (& therefore the groove) was reinstated, & 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, & competent transmission overhaulers DO, modify the non-circlip shaft, but this needs to be done very carefully. It can NOT be done if the gear mounting area has tapered from the gear wobbling. 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 SUPPOSEDLY had the circlip re-installed. DO NOT DEPEND ON BMW's BULLETIN INFORMATION USING THAT SERIAL NUMBER!! It is my belief that you CANNOT DEPEND on even a 1995 bike as having the circlip. See my list of reported transmissions, much later in this article. You CANNOT DEPEND on a late 1984 to have, or not have, the circlip. Still, the best information, if your transmission isn't being taken apart, will be had by looking at the transmission serial number. Even THAT is sometimes questionable, if you look at the charting later on this page. However, it seems likely that MOST 1984 transmissions are going to be OK. It presently appears that 1995 is going to be mixed, with most (??) being OK.
NOTE as said at this article's beginning, some 5th gear movement has been seen now & then ...even with a circlip installed.
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 on the top rear center or top front center, where you can not see it without removing the air cleaner assembly. In 1978 (& until the serials were put on the left outside, in approximately 1984), the serial was on the FRONT INSIDE FACE of the casting. Thereafter, the serial number is located at the top area of the left side, JUST BARELY BELOW where the left rectangular 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 so noted below.
When reading in this article about 'year', be advised that BMW's 'model year' includes motorcycles that were built near the end of the prior year, & it is quite possible to see a build date as early as September, to be included in the following year's models ...and, there is occasionally an anomaly & an even earlier than September-made model will be dated in the following calendar year. Except for anomalies, this is due to BMW policy of closing the company for the annual month-long holiday (vacation). A September, 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.
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).
NOTE 1: The 1978 transmissions had gusset reinforcement running ONLY from front to rear (NONE left-right). Beginning in 79 the gusset reinforcements at the bottom of the case were cross hatch like a crossword puzzle. Changed was the shift linkage. It now pivoted from the footrest, & was more positive. 1979+ transmission cases were RIBBED. This ribbing makes the cases stiffer, preventing, mostly, any change in shimming dimensions with high mileage.
1982:Z-036600 -> Z-060400.
5-speed transmissions; Circlip/Groove tabulation; reports from owners & overhaulers:
For many years, I have been collecting information on Airhead motorcycles that have had KNOWN, by disassembly, circlip-less FIVE SPEED transmissions ....and some reported on that WERE found with circlips. I try to especially select for this article those transmissions that were likely never opened previously for repairs; obviously, that is not going to be 100% perfect, but there ARE telltale signs that are often quite usable. In a few instances I have added information to the charting of transmissions WITH the groove & circlip, where such information may be helpful. Information received, AFTER I INDEPENDENTLY CONFIRM the VIN, serial number, year, month of production, etc., it MAY be posted to this article in this section,
always withOUT identifying the owner's or overhauler's name. Some few transmission reports are not usable and I have been unable to get the needed information. In a few instances the information is so not pertinent that I have not included that motorcycle nor transmission.
Effective January 1, 2017, I want to receive ONLY information on 1983-1985; & 1994-1995 transmissions, both with & without circlips, as found. If no circlip, if the shaft was grooved, or not. The idea is to identify, if possible, earliest & last date of bikes with such transmissions. I am still interested in receiving that information. Please provide FULL VIN number & FULL transmission number, & any pertinent information, such as if the transmission was ever opened before. If no 17 character VIN number, please provide what information you can, from right side frame stamping, dipstick area serial number (if present), and information stamped into the milled boss area below-forward of left cylinder. As much information as possible is requested. Information published in this transmission article DOES NOT identify you. http://bmwmotorcycletech.info/emailimage.htm
There have been NO motorcycles reported to me that were built in calendar year 1983, that had NO circlip.
1983-1984 motorcycles. This section was done separately, as I felt it was quite important to TRY to identify any transmission serial numbers and VIN or other vehicle numbers, to see what the earliest NO CIRCLIP models might be.
a. R100RT, USA model, transmission Z094331, VIN WB1044904E6243388. This bike was reported to me as HAVING the circlip (& the wire clip located at it). The E in the VIN shows it to be a 1984 USA model, but, the serial number, 6243388, shows it was built June 15th, 1983. This dating anomaly is not uncommon for 1983-1984 bikes.
b. R80RT, 1984 USA model. HAD the groove, DID NOT have the circlip. This transmission definitely had never been opened. Transmission Z105671, VIN WB1044802E6173763, production 03/1984. The left side engine boss shows: 14 847395. Thus, this engine/bike was made in the 14th week of 1984. This goes right along with the BMW internal information of the motorcycle being built in March 1984, & the serial of the production is 7395. All this seems to be reasonable. Note that other characteristics of this motorcycle back up its production dates, such as not having dipstick area serial stamping, a driveshaft tag with the E year same as the stamped VIN.
c. R100/T, version is USA R100CS last edition. VIN WB1043502E6177343. Transmission Z105851. This transmission was likely opened previously, perhaps for a broken pawl spring. This transmission was found to have the groove, but NO circlip. The production was confirmed in several ways.
d. This is another 1984 bike I know about. I have been unable to confirm that the transmission had never been opened up, but believe it is so. This is an Australian bike. The milled-boss area shows 33 845294, meaning the 33rd week of 1984. This agrees with the vehicle identification number stamped into the right lower frame tube: 6354483R65LS (yes, not a 17 character VIN). It also agrees with the Australian Compliance Plate (which was not riveted over that frame tube stamping just noted ...it was riveted ahead of it ....so both could be seen. The plate said R65LS and 6354483. The transmission number is Z 108683. HAD groove, NO circlip. BMW sources confirmed a build of 08/1984, ECE (Euro) model. Note, another number that was on the bike: 33845294652VB ...no information so far on that.
1985 R80 USA, transmission Z111812, VIN WB1046307F6480009, production 12/1984, no circlip, but shaft had groove, original owner, never been apart before.
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
1985 R80RT, transmission Z114405, VIN WB1046400F6490413, production 2/1985, no circlip, no groove.
1985 R80, transmission Z114317, VIN ending in 6480354, production 2/1985, no circlip, no groove, transmission known to have never been opened previously.
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, USA model, transmission Z124295, VIN WB1046306G6480598, production 10/04/1985, NO circlip; virgin unopened transmission.
1986 R80, transmission Z125576, VIN WB1046303G6480655, production 10/1985
1986 R80GS, transmission # unknown, VIN WB1034801G6363284, production 10/1985
1986 R80GS, USA model, transmission ZA126409 (with kickstarter as shipped from factory), VIN WB1034802G6363343, produced 11/25/1985
1986 R80, transmission Z128362, VIN WB104630XG6480782, production 12/1985
1986 R80, USA, transmission Z135754, VIN WB1046301H6480851, production 07/1986, yet has H identification which makes it a 1987 model. This bike was a California model, ordered by distributor (?) with two front discs.
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 R100GS, transmission 0198991AA1, VIN WB1048808N0230445, production of 07/1991 (officially ID'd as a 1992 model by the VIN, etc.). NO groove, and hence no circlip.
1992 R100R, transmission 0204810AA1, VIN WB1048701N0280119, production of 10/15/1991, no groove, and hence no circlip
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/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 R100RT, USA, transmission 0221583AAB, VIN WB1046903P6293892, no circlip, no groove, production 09/08/1992.
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 0228652AAJ, VIN .....646450, production 01/1993
1993 R100GS-PD, EURO, transmission 0232033AAJ, VIN 0069483, no circlip, no groove, production 04/01/1993
1994 R100R, transmission 0234197AA1, VIN WB1048705R0280808, production October 27, 1993
1994 R100RT, USA model, transmission 0236278AAB, VIN WB1046904R6294018, production 09/03/1994. No groove, & no circlip of course.
1994 R100R, transmission 0236159AAI, VIN WB1048708R0280799, production 09/10/1993, USA model. Preventative maintenance was done at 80K miles, gearbox never previously opened, no problems with gearbox. NO circlip, NO groove.
1994 R100R, transmission 023696AA1, VIN WB1048709R0280858, production 01/1994
1994 R100R, transmission 238655AA1 no details furnished
1994 R100GSPD, transmission 0238596AAJ, VIN WB1048408R0340374, production 01/1994 ECE model, no groove.
1994 R100GS, transmission 0237931AA1, lug stamped NI
1994 R100GS, transmission 0238984AA1, VIN WB1048805R0231610, production 01/1994
1994 R100GS, transmission 0238225AA1, VIN WB1048801R0231538, production 01/1994, USA model, no groove.
1994 R100R Mystic, USA model, VIN WB1049705S0400201, had clip & groove. Production 09/28/1994. Transmission number unknown, never reported to me.
1994 R100M, transmission 0240810AA1, had circlip. VIN not reported, 1994 assumed.
1995 R100GSPD, transmission 0246168AAI, VIN WB104890XS0048207, production 01/05/1995, USA model. Purchased new. HAD circlip.
As you can see from all the collected information, it is not easy to determine if YOUR bike's transmission has a circlip, or not. Note the strangeness of the 1995 models, above.
Compare to earlier years too. Note that some 1995 production bikes, AFTER the BMW official bulletin date for reinstatement, had no groove/circlip. I need more info on pre-1985 and after 1994, many more, to try to determine transmission transition numbers.
Bottom line: It is "possible" for any Airhead built from end of 1983, as a 1984 model, to the end of Airhead production, to NOT have the circlip. BUT: there is not yet proof of any built BEFORE March 1984, without the circlip.
Viewpoints on the circlip 'problem':
#1: This is the much more commonly accepted viewpoint & one I personally agree with:
The front gear teeth on the output shaft is manufactured on an angle, that is, the gear is HELICAL cut. Its mate obviously must also have that cut and must have the same angle. Picture in your mind such a pair of helical meshing gears. If power is fed to ONE, then the other has force such as would try to move that gear along the axis of the shaft, not just 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. Simplified: 5th gear pushes 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 moving on the shaft. Because of this, the front bearing is always damaged, and sometimes the rear bearing, and even the rear cover plate! ....all happening when there is no circlip to prevent (one hopes) movement.
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 would make them heat up, and then 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 (those bearings are also VERY pricey).
Prior to probably late 1984, there was a hardened snap ring, a CIRCLIP, that fit in a machined groove on the output shaft, it was just forward of the gear, & 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. There is also a tiny spacer clip, almost a wire clip in size, alongside one end of the bearing, more on that later.
When the circlip is not installed, axial thrust from 5th gear still tries...& may well actually cause, the gear to move/push the inner race of the output bearing ...along the shaft towards the front of the transmission, as the shaft, in essence, moves rearward & 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 & fail.
SO: the large front bearing overheats, begins to self-destruct (the cage which keeps the balls in place starts coming apart & metal goes all over the place inside the gearbox). More clearance develops, the output shaft can actually wobble in the bearing. This will, of course, start tapering the metal on the shaft; that RUINS THE $$$ SHAFT. If bad enough, the output flange on the transmission (driveshaft U-joint flange) contacts the transmission lip area where the boot is, & the output rear bearing distorts; &, with metal bits already getting into things, all sorts of mechanical mayhem happens, & rather quickly.From the first sign of unusual vibration, things deteriorate rather quickly. If allowed to proceed, gears, bearings, shift fork, & even the rear case of the transmission, are ruined. #2: This is a far less-accepted viewpoint. I am not sure anyone still thinks this way:
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.
Below is the 'improved' bearing, SAME part number, note the TM on the bearing.
MORE on the 6403 bearing! (READ CAREFULLY, and compare with above information!):
The following was copied from the Airheads LIST on 06/21/2017. The reason I am placing it in my transmission article is for 2 reasons. (1) is that it fully explains, together with the above information, what you need to know about the versions of this bearing. (2) is so you will have a good idea of why most owners send their transmissions out for repair to qualified WELL-EXPERIENCED with AIRHEAD transmissions Specialists. In this case, the Specialist is Tom Cutter who does business as the Rubber Chicken Racing Garage, located at 1360 Colony Way, Yardley, PA, 19067. TPCUTTER2@aol.com (215) 321-7944.
I have edited this slightly for ease of reading, but have not edited out mistakes on part numbers. Brook Reams asked: This bearing (part# 23 12 1 233 808) has a rubber cover over the race on the side that fits into the hole in the rear cover. QUESTIONS: 1. Why is this the only bearing with a cover? Tom answered: That is a 6304 C3 2RS2 sealed bearing, with one side seal removed. BMW did that to create an oil reservoir between the bearing and cover, where particles of swarf could accumulate, and remain trapped. This also directed as much oil as possible down the center of the intermediate shaft, improving the lubrication of the free-wheeling gears on that shaft, which are turning, relative to the shaft, all the time when you are in top gear. The bearing itself gets enough oil from the shaft churning in the oil (it is partially submerged in the oil when the level is correct). Be aware that the BMW parts fiches have for several years listed the location and quantity of that bearing incorrectly. The half-sealed bearing goes on the REAR of the intermediate shaft ONLY. The open -495 bearing (also a 6304 C3) goes on the front (closest to the helical gear) end of the intermediate shaft as well as on the rear of the input shaft. The rear of the output shaft ALSO gets a -495 (also a 6304 C3) bearing on the non-paralever models, The paralever models get a FULLY-SEALED (also a 6304 C3) bearing at the rear end of the output shaft, part number 23 12 1 338 466. Tom further said: Confused yet? Build a couple thousand BMW gearboxes and you will appreciate that there are hundreds of little details to know about the internals, changes, what works wit what, etc. This will be my last public post about internal transmission stuff, because it is not a task that has a forgiving learning curve. People get hurt and killed when transmissions fail on motorcycles. I don't want to be the one who made people feel that a few tools and some Internet learnin' will do it.
2. The new one I bought does not spin as freely as the other bearings that don't have the cover. I assume the cover adds some resistance when the bearing rotates. Is this normal?
Brook Reams asked: This bearing (part# 23 12 1 233 808) has a rubber cover over the race on the side that fits into the hole in the rear cover.
1. Why is this the only bearing with a cover?
That is a 6304 C3 2RS2 sealed bearing, with one side seal removed. BMW did that to create an oil reservoir between the bearing and cover, where particles of swarf could accumulate, and remain trapped. This also directed as much oil as possible down the center of the intermediate shaft, improving the lubrication of the free-wheeling gears on that shaft, which are turning, relative to the shaft, all the time when you are in top gear. The bearing itself gets enough oil from the shaft churning in the oil (it is partially submerged in the oil when the level is correct).
Be aware that the BMW parts fiches have for several years listed the location and quantity of that bearing incorrectly. The half-sealed bearing goes on the REAR of the intermediate shaft ONLY. The open -495 bearing (also a 6304 C3) goes on the front (closest to the helical gear) end of the intermediate shaft as well as on the rear of the input shaft. The rear of the output shaft ALSO gets a -495 (also a 6304 C3) bearing on the non-paralever models, The paralever models get a FULLY-SEALED (also a 6304 C3) bearing at the rear end of the output shaft, part number 23 12 1 338 466.
Tom further said: Confused yet? Build a couple thousand BMW gearboxes and you will appreciate that there are hundreds of little details to know about the internals, changes, what works wit what, etc. This will be my last public post about internal transmission stuff, because it is not a task that has a forgiving learning curve. People get hurt and killed when transmissions fail on motorcycles. I don't want to be the one who made people feel that a few tools and some Internet learnin' will do it.
Here is an EDITED (by me) query & reply, from the Airheads LIST in November 2004, that will explain about something you might otherwise overlook if you are overhauling a transmission, ETC:
The transmission was from a 1983 or 1984 R100RS. The owner decided to do an overhaul. It had been done previously, probably by him; the mileage was now around 200,000 km. He noticed a small "rumble" or notchiness 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 magnet.Transmission was removed & he slightly released the gearbox cover screws (1-2 turns) & the notchy feeling disappeared totally. Sounds like a preload problem?? The owner then measured the clearance between the output shaft snap ring & 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 & 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 & the bearing inner race to zero clearance.
The owner continued....(Snowbum 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 (slightly edited, mostly just emphasis here by Snowbum, only SOME of which is in red color):
This round wire expansion ring sits down in the radius of the bearing bore, & effectively fills the void so that there is metal-to-metal contact from bearing to circlip (snap ring). The circlip is: 07-11-9-934-100 (size 17 x 1). This is the same circlip used on the shift shackle in the transmission, in case you get curious about it.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, & 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, & these numbers, don't trust me here. The groove must be VERY precisely located & done so that the round wire expansion ring, mentioned above, CAN be installed. The inner race of the bearing we have been 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 & circlip). MY feeling is that if things are done precisely, then the expansion ring must be installed. However....I have mixed feelings on that.
More on the machining, and presented differently. Oak drew a sketch with his usual very specific and accurate dimension numbers on it for the machining:
From the shaft face that the pressed-on bearing can be fitted against, the circlip groove begins at 0.6693" to 0.6713". The shaft bearing fitment area is ~0.670" diameter, for the pressed-fit bearing and the cut begins at 0.6693 to 0.6713". The circlip groove begins at the number noted, and proceeds to the shaft end, with a groove cut to 0.0394" to 0.0400" in width (Oak said the maximum was 0.041"). The groove must be cut square without radius in the cut. The depth of the cut is 0.020".
Here is another article with photos. Be sure to look at this one: http://www.largiader.com/articles/circlip/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.
The throwout bearing area:
This is being put into this transmission article due to the potential for someone to think that the transmission itself has a problem. It is expanded upon here: http://bmwmotorcycletech.info/clutch.htm
Typically, the clutch will start to slip, when the transmission gets fully warmed from riding. There have been instances of stiff clutch, or frozen or nearly so clutch operation (NOT same as clutch disc sticking to flywheel in humid climates ...for that, see clutch article, above link).
The 4 speed transmission & the early 5 speed transmission (pre-1981) clutch push rods had felts located in a groove on the pushrod; are installed best from the front, as installing them from the rear will require a special tapered tool you must make. The 1981+ transmissions did not use a felt; had a rear SEAL instead; the rod should be installed from the rear ONLY. The rod is stronger, & aluminum ones better match the transmission changes with temperature. 1981 & later models have a lipped seal at the rear cover for the pushrod, that is not easily replaced ....the transmission must come apart. Install THAT pushrod, oiled, FROM THE REAR, rotating it a bit, to avoid damaging the seal (which you will, if you install from the front, like you do on earlier transmissions & clutches).
The 4 speed transmission had a balls-type throwout bearing. The early 5 speed transmission had a radial needle bearing. From 1981, BMW BMW went back to the ball bearing. The radial bearing is a poor design, & if it fails, the needles can flat-spot, the bearing can seize, etc. HOWEVER, that is RARE. MOST throwout bearing failures are due to moisture getting into the gearbox!
See the NEUTRAL SWITCH article on how to replace a neutral switch on a 5 speed transmission: http://bmwmotorcycletech.info/neutralswitch.htm
Removing a transmission from the motorcycle:
For twin rear shock absorber models, remove the U-joint 4 bolts, remove the entire driveshaft & rear drive & swing arm completely; or, loosen the swing arm pivot pin locknuts (27mm) & remove the pins (allen wrench). Do this carefully to avoid thread damage, then use bungees or rope to pull the rear drive to the rear somewhat. You can then loosen the top battery mounts, tilt the battery mount rearwards a bit, remove the battery, and then remove the transmission, how is obvious. Protect the frame paint, protect the clutch lever mounting bosses (I remove that lever), remove the air cleaner items. This is not a step by step procedure, and you will find things I did not mention ....that are minor.For the Monoshock bikes, it is similar...but NOT the same, particularly on very late models ....and, see below too:
Replacing the input shaft seal:This can be relatively easy, or can be difficult. Often 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, which then slips. When you have the transmission either out (or backwards some), to do the normal scheduled input spline cleaning & 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 or 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 you 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 cleaner to get all the drilled metal pieces into the vacuum cleaner, not the transmission. Some use small drywall type of screws (BE CAREFULL!). Remove the center of the seal 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 & if needed clean up the mounting area very carefully, using fine grit sandpaper if you have to, & use the 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.
MORE Transmission information:
Excessive end play of the transmission input shaft can cause a quite-grabby clutch operation. It can happen cold and/or hot, but more often when hot. To fix this, one must remove & open the transmission & work on the shaft shimming. One can get an idea if that is a problem by removing the transmission, heating it to about the temperature of boiling water & 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 ~ 0.005". This problem with transmissions causing a grabby clutch is not very common, but it seems to be more so for the 1979 models. Another cause is excessive end-play on the crankshaft. That is rather rare, ~ .007" is the maximum I personally would allow, & that is for a DRY assembly, which means you cannot take a measurement that means much, when oil is in the end parts! Note also that other things can cause a grabby clutch, including the throwout bearing & the throwout bearing piston being slightly too large in diameter.
Excessively worn crankshaft bearings can cause transmission rattle noises, but this is MUCH MORE RARE than the rattle noises at idle with hot transmission oil, described much earlier in this article.
The 5 speed transmissions weighs about 24 pounds, without lever and without 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; some modest amount is in http://bmwmotorcycletech.info/models.htm. The 1974 transmission is a special instance. This was the transition year for BMW, from the /5 to the /6. 1974 was the first year for the 5 speed box. There were some things not good with the 1974 transmission. The Pawl springs tended to break. The kickstart parts were SOFT & use of the kickstarter is NOT recommended. There were problems in positively locating the Neutral position, & that wasn't fixed until later. NOTE that the FIX for the neutral position was done BEFORE the "Shift Kit" was installed by BMW. The Shift Kit addressed other problems; many confuse these things. The 1974 transmissions, in other words, did not hold up well. Some parts are no longer available. This parts problem extends into the 17.5 & 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). When you see the parts prices, you will scream. If a 1974 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, 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 what was mentioned above, the seventies 5 speed transmissions had a habit of breaking the gear dogs off. The gear dogs & 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 typically find one or two dogs broken off & in the drained oil. Cause was the shape of the dog AND the lousy machining, it wasn't perfectly at 90 degrees. One dog carried nearly all the load; broke off, then another might break. Ask about this ON THE AIRHEADS LIST if you are confused, or, perhaps you want to know if you can continue riding ....a big maybe.
Here's more information on a variety of transmission things:1. http://www.largiader.com/tech/airtrans/ Has a number of photos & descriptions that you may find very useful in understanding the 4 & 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 & 'shift kit', etc. I recommend you review that article ....and the links at the bottom. Note that 17.5° gears were supposedly installed from 1982, & I am not at all sure that is totally correct. CONTRARY to what Anton says at the bottom of his article, regarding MY article that you are reading, stating that I cover mostly 'historical' information, I cover a huge amount more than just history. I suspect Anton looked at my article, & did not scan down very far. I get into more depth on things, including the 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. Anton's article now has photos showing how the cam changes fixed the neutral finding problem, and, later changes in the Shift Kit, that came about in 1981+. MANY have confused these fixes, as BMW made changes to improve neutral-finding many years before that.
The Paralever output shaft oil seal open side faces FORWARDS. If having oil transferring from the driveshaft into the transmission, you CAN reverse the output seal of the transmission, so the spring is REARWARDS. A new style seal is now being used on the Paralevers, install dry, shaped for a couple hours on some sort of mandrel, & then be 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. The new style seal used on R100 GS transmission output: http://bmwmotorcycletech.info/SI-00-053-88-new-style-seals.pdfIf 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 & drill it 1mm. Later models have this already modified.
4. There are quite a few things that don't readily appear to someone taking apart a gearbox. For a truly good operating gearbox, that is smooth, positive shifting, and will LAST.....you WILL ...or should......consider a specialist.
5. 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.6. As you have already read about, MANY changes were made to the transmissions over the years. But, there were many more I did not get into. There are DOZENS of these 'nice to know', or 'NEED to know' items. 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 AIRHEAD 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; nor, all the models at the same time. The OFFSET segment for pawl spring clearance was one such change. Several changes occurred at serial Z5A79720.
7. The /6 kickstarters should not be used much. I'd never use it unless necessary. The 1974 was weak. NEVER just jump on the kickstart lever. Be SURE it is properly engaged. MY method for ALL years & models of kickstart transmissions is to use light foot pressure, until ...or if ... 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 (full mesh). This ensures proper engagement. Release the clutch lever, keeping light pressure on the kickstarter lever. THEN, push the kickstarter down briskly.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. I recommend the 4 speed kickstarter shaft be modified with a drilled and tapped hole, and apply blue Loctite to the added screw and use a large washer. Information and a photo are well below in this article.
8. Improved shifting parts, for external linkage mounted off the footrest, are probably still available as a kit, for the earlier 5 speed transmissions. The design change occurred in 1978.
9. In 1981 BMW made changes in the transmission-located clutch throwout bearing area, internally as well as to the external shift lever. Also in 1981, BMW made a large change to the clutch & flywheel, which became a totally different design, & the flywheel was now called a Clutch Carrier, & the transmission input shaft was made shorter to accommodate those changes. 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; internal gears angle cuts; shift kit or not; proper neutral switch ...etc ...as all mentioned in this article, most transmissions generally interchange. Pay attention to the Monolever & Paralever versions.
10. Shift kit and pawl spring, etc:
Inside your transmission is a detent 'Pawl' 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, & then shift into a gear, maybe. I've heard of this, never done it myself; especially since I have never had a pawl spring of my own break.
In the transmissions I have worked on, I make sure the pawl spring cannot break from being around a too large boss, but there are other considerations too.
There are homemade tools that you can make that you stick into the transmission oil level hole after removing the threaded oil fill/inspection plug. It is tricky to use the tool, 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, with pictures and construction information: http://bmwmotorcycletech.info/emergency-shifting-tool.htm. Any such tool will be difficult to use without practice. NOTE that the tool will enable you to shift into any gear you want, but NOT during riding! Use of 2nd gear would be the most likely practical gear to leave the transmission in. 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? The early spring rubs on itself during operation, wearing itself thinner. The spring may wind too tight on the large boss, causing excessive force on the spring. Possibly some faulty springs, possibly a few other things.
Prior to the shift kit, BMW had made changes to help eliminate the sometimes false neutrals. The shift kit was to fix several problems, the major one being over-shifts, due to the lowering of clutch and clutch carrier (prev. called Flywheel) inertia from lighter weight. It is, however, true that some shifting improvements in the neutral finding were incorporated, but not to the extent you may think. The kit is part number 23-31-9-056-150. The kit as such is no longer available, but the parts ARE. The shift kit 'fixes', or at least additional help for false neutrals do not have the same level of improvement in the heavy flywheel models as the later clutch carrier models. http://www.largiader.com/tech/airtrans/ is a page on Anton's site that shows the primary upgrades for the neutral; and, the shift kit, with photos.
To make this very clear: The shift kit was installed by BMW in some models in 1981 and all by 1982 and later, PRIMARILY to fix over-shifting during gear selection. This was for the Clutch Carrier models, which, being much lighter, reduce the inertia of the rotating mechanism, compared to the heavy flywheel models. The Shift Kit is no longer available as a Kit. There are some reliability improvements by installing the Kit parts into a heavy flywheel 5 speed, but the shifting improvement is small to modest, although it IS noticeable.As mentioned earlier; numerous parts changes in the shift mechanism occurred over a number of years ....such as the offset segments and pawl spring changes.
11. 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 models), because these have the lightened Flywheel, called a Clutch Carrier. The shift kit might improve earlier transmissions slightly to modestly, certainly the pawl spring breakage problem is lessened. Using pawl 23-31-1-242-892; & Segment 23-31-1-231-578, supposedly will 'cure' broken pawl spring problems ....but; modifications to the stock boss (as discussed earlier) and/or use of the upgraded spring work well for that particular problem. The shift kit will help IF the early heavy flywheel has been lightened. The shift kit did NOT come with any instructions.
I would not put the shift kit into a stock early heavy clutch/flywheel motorcycle unless the owner understood the cost, and what will be helped, or not. Certainly, the earlier transmissions can be re-worked without the Kit parts, for improved reliability, as noted well above, such as boss size changes, etc. There is no problem learning how to do the nice slightly slower shifting with the old setup. Pre-pressuring works delightfully.
Note what I said much earlier in this article: The thickness of the OIL has a substantial effect, depending on temperature, as to shifting characteristics. The oil …and quite a few other factors in the gearbox design, have an effect on how the gearbox parts slow down, as you attempt to shift downwards. That is ONE of the two reasons (the other being cold lubrication) that I do NOT recommend anything but 80W90; or 75W90 gearbox oil, GL5. The speed at which the slowdown (or speedup) happens affects how the gearbox seems, to you, to shift; going up a gear or going down a gear. Shifting speed is not just something involved with the 'shift kit', it is also involved with gearbox setup, and some of the many changes made in the gearbox for various reasons. If you were installing a lightened flywheel, you should consider the kit.
BE SURE, 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 available parts:
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)
Using pawl 23-31-1-242-892; & segment 23-31-1-231-578, supposedly will 'cure' broken pawl spring problems ....but modifications to the stock boss (as discussed earlier) and/or use of the upgraded spring work well for that particular problem.
NOTE the following ....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):
Tom Cutter posted the following to the Airheads E-mailing LIST in September 2003; it clearly states what the kit also does, & I quote (typos corrected by me) (comments by me, snowbum, are clearly marked in RED):
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 & I disagree a bit on the subject?
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 to be used. The 1974-5 neutral switches have a shorter stem. If you install the wrong switch, it does not work correctly, and there may be shifting problems!There are TWO sections in the http://bmwmotorcycletech.info/electricalhints.htm article on this website on the neutral switches, neutral lamp, starter circuit, and problems. It is complex!
There is a diode in the neutral circuit. If that diode shorts, the lamp is ON if the lever at the bars is pulled. There is also a peculiarity with some of the 1978-80 models, which have a master
cylinder under the fuel tank. These 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. If the diode shorts, and you are also low on fluid, the starter could theoretically energize. I suspect this is VERY rare. The RS and RT rear disc models from that era may have a rear master cylinder float switch.
12. The 4 speed transmission & early 5 speed transmissions can be difficult to find parts for, & difficult 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, and some others.
13. 5 speed transmission gear ratios:
|Stock||Competition/Race. The gear set is
23-21-1-233-427. I have never seen this gearset, & wonder if any were ever sold??
14. There is an additive that SOMETIMES will help smooth the shifting, particularly with transmissions with the original older style shifting parts. It is Dow Corning M Gear Oil Additive. Comes in quart bottles. Shake well and use up to 2% concentration maximum.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 & do NOT add more than 20 cc!!!!
16. 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, & 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 & 4th, & the shaft which had been 100 mm is now 105 mm long. In 1979 the case was stiffened with ribs for help with shimming changes being needed at high mileages, from case stretching.17. 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.
The FOUR speed transmission kickstarter idler gear shaft is press-fitted into the rear transmission cover. There is a tendency, particularly when 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 inwards into 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, parts inside fall to the bottom. The simple fix involves drilling & tapping the shaft, adding a small bolt and large washer.
In one instance I remember from years ago, the shaft had started to move. The owner drilled the shaft, added a large flat washer & bolt; heated the rear cover & use the bolt to pull 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 and squarely. Thread the hole (use a metric size), add a large flat washer larger than the shaft diameter, & use Loctite BLUE on the STEEL screw you will add to hold the washer to that shaft. That washer prevents the shaft from moving inwards. Use some sort of goop sealant between the washer & 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 & cover mating areas; 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 as noted in the earlier paragraph. Don't use too small a screw size, and use a decent amount of heat.
BEARINGS:4 speed transmission:
5 speed transmission:Regarding the 6403-C3 bearing 'where the circlip is' : BE SURE to read the notes well up this article on this bearing, and the associated photo of it.
In 2005, Matt Parkhouse did a series of articles in BMWMOA-ON, on overhauling the 5 speed transmission. GOOD articles.Anton's transmission article. Highly recommended: http://www.largiader.com/tech/airtrans/. 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, SOME information on what can & cannot be substituted; what won't fit, etc.
With regards to this LINK, I have NOT gone over the instructions step by step. While there are plenty of tricks, etc., that are not in the article, it SEEMS to be complete enough that YOU MAY be able to do an overhaul.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. http://jhau.maliwi.de/mot/gearbox.html then click for gearbox.
Preloading the Shift Lever, what it does to help make smooth transmission shifts:I will try to simplify this....well, somewhat. Taking a bit of license here on the explanations.
Brunos, in Canada, has a very good reputation. No personal knowledge, but trustworthy & competent from what I have heard. However, I have been told that Bruno Sax is quite ill, and may not reopen his shop.
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, 812-472-3739. He ALSO does reverse gear conversions (still doing them ??) to the 5 speed transmissions; some information on this particular conversion will be found in http://bmwmotorcycletech.info/sidecarURL.htm on this website. Has a good reputation.
Motorren Israel also does a different type of reverse gear conversion.
Motor Works, Inc. 1490 Island Ave. San Diego, CA 92101 619-233-8875 email@example.com Not enough personal or reported information.
All referenced transmission specialists in this Snowbum's article you are reading, can probably do conversions, such as changing first &/or fifth gear ratios, in 5 speed transmissions.
DYI (Doing It Yourself) (part 1):
If you want to open a transmission for minor work, I have no serious objections. However, of all the things that might need major repairs on your motorcycle, the transmission is the most detailed on what to know, how to go about doing it, etc....in particular because of so many changes over the years. Snowbum no longer has his transmission overhaul tools and jigs, and would no likely overhaul his own transmission now. He'd probably send it out, see the above list of folks and my comments.
NOTE....The above articles are possibly not complete, & MAY have errors. They are listed here strictly for the purpose of you getting some ideas about the scope of the work, how things work and are assembled, ETC. Read the next section,
DYI (Doing It Yourself) (part 2) for more information.
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 can be farmed-out).
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):
Gear change lever shaft axial float on 4 speed: as above.
Fork bolts 17 footpounds (& 4 speed)
Output flange nut 160 ftlbs (clean and dry on the tapers! ...absolutely NO residual oil!).
End cover nuts 6 ftlbs.
Selector fork/cam bracket: 18 foot-pounds (from 1981, 14 foot-pounds)
Axial float on all shafts: 0-0.1 mm (0-.004 inch).
The original shafts end float was 0.004". From 1981, BMW used 0.002", and I think 0.002" is best for all of the transmissions. Note that this is ~ the same as the 0.05mm in the books.
DYI (Doing It Yourself) (part 2):
This section was posted by Tom Cutter to the Airheads LIST on June 10th, 2012; in response to questions. I have NOT edited this except for paragraph separations added & to fix a couple of miss-spellings, grammar corrections, and a note or two from me. I have left in one or two questions from the original poster, to whom Tom was replying (and, the entire LIST membership too, of course). My purpose in putting this posting here is to give you an idea of what is done by a professional who has done a lot of these transmissions.
"When I do a gearbox job, I heat the box in the oven to 225F, then turn the shafts by hand, shift the gears up and down, and push-pull the input and output shafts to check for grossly excessive
free-play. Then I strip the whole gearbox down to the last component, throw everything into the parts washer, turn on the air agitator and go pull the new parts, write the part numbers on the customer bill and on the reorder list, then come back to the clean parts. I rinse the parts, polish the shifter shaft, wire wheel the gasket surfaces, and lay it all on the long table for individual component inspection. That is the most time-consuming part, because each part gets inspected, compared and evaluated for either the "SAVE" or "REPLACE" pile.
Establish the proper spline lubrication interval for YOUR bike, YOUR riding habits. You will avoid $$$ repairs. 07/07/2008: Prior updates incorporated & minor editing for clarity including groove depth; add hyperlink to Anton's site. © Copyright, 2014, R. Fleischer
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. At 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 than 10 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 & slip the shift shaft into the forks & the housing bore.
The shift cam-plate 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 onto the cover (and until 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 & test it for continuity, I run the shifter through all the gears, install the drain plug with a new gasket & the fill plug is lightly screwed on with a large bold tag that says "ADD OIL!" along with recommendations for oil type & quantity for the particular gearbox. I install & grease the clutch throwout bearing & piston assembly, the clutch pushrod & actuating lever assembly. Everything gets wrapped in a clean plastic bag, swaddled in protective bubble wrap & 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 transmission input splines must be lubricated regularly. Nickel-plated ones supposedly became standard on 1984 Monolever bikes, that let you go considerably further between cleaning & lubrication intervals. I am not much of a believer about shafts being plated from then. Transmission spline lubrication is covered elsewhere's on this website, in article #43: http://bmwmotorcycletech.info/inputsplinesthrowout.htm
Revisions: (updates for bike serial numbers, transmission ID & VIN are not usually listed here as a Revision)
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, & 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; 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 some repetitive stuff.
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 repetitive things.
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 & 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 wording for 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.
sometime in 2013: remove language button.
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.
09/27/2014: Clean up, including changes for better utilization on smaller screens.
11/06/2014: Minor changes, plus add considerably to 9B.
08/05/2015: Clear up typos and missing words in section 9A.
08/25/2015: Fix unclear statement early in the article about circlip not being a 100% fix all the time.
10/03/2015: A few minor changes for clarity; plus, updated serial/groove/circlip information.
10/11/2015: Clean up article some. Fix things for more clarity. Fix a few bugs.
12/01/2015: Fix meta-coding, re-arrange article considerably; cleaning things up as I did so. Article is still messy, needs more cleanup & combining, re-arranging.
12/23/2015: Finish meta-code updating & narrowing. Consolidated sections, greatly reducing scattered information, etc.
01/10/2016: Conclusions about circlips versus years, etc.
04/22/2016: Major update to metacode, layout, colors, fonts, separations, reduce redundancies. Move certain items to other sections. Re-number some sections. Add .pdf for factory gearbox and clutch.
12/08/2016: Improved shift kit explanations.
From 12/23/2016, and finishing 01/02/2016: Line by line go through entire article HTML code. Reduce excessive code, improve clarity, clean up fonts, horizontal lines, colors, metas, scripts, etc. Article being revised for clarity, excessive HTML, improper H.L., fonts, colors, metas, scripts, etc.
05/25/2017: Additional dimensions added to the circlip position and cut.
06/21/2017: Add Airheads list exchange between Brook Reams and Tom Cutter, regarding "6304" "6403" bearings....
07/23/2017: Removed a red separation line in the section about the confusing bearings, otherwise readers might miss the last part of it. Moved things about a bit, for additional clarity. Added to DIY and to recommended Servicers.
07/24/2017: Fix two typos: (1) date was 07/23/6017. (2) One place, 6403 was 6404, in area "Regarding the various 6403-C3...."
Return to HomePage
Establish the proper spline lubrication interval for YOUR bike, YOUR riding habits. You will avoid $$$ repairs.
07/07/2008: Prior updates incorporated & minor editing for clarity including groove depth; add hyperlink to Anton's site.
© Copyright, 2014, R. FleischerReturn to Technical Articles LIST Page
Last check/edit: Monday, July 24, 2017