BMW AIRHEADS: 4 & 5 speed transmissions
Oil types for your transmission. Noises. Rattles.
Output shaft snap ring (circlip) & groove problems.
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.
Doing It Yourself.....etc.
MORE throwout bearing information is here:
Preliminary & Introduction:
Many folks have problems understanding, let alone visualizing, how a BMW transmission
operates. I am putting 5 links at the beginning of this article to help with understanding.
Link #2: 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 #3: This shows BMW GS transmission. Review this for shifting & various noises, etc. http://micapeak.com/bmw-gs/trans.html
Link #4: http://w6rec.com/duane/bmw/trans/index.htm 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.
OIL:BMW has never waivered in its transmission oil recommendations, and this includes right up to 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.
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 said that you could use
75W90, 80W90, or 85W90. 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.
one 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 you CAN, if you want to, use a synthetic gear oil of high 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. I think 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/brand 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. NOTE that 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". You can use it in 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).
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 ending in 120 or 140 or even 145 (& to a lesser extent with synthetic), will take the transmission operation out of the design operating area, as far as gears & parts speeding up & slowing down during shifting, 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 air temperature, lubrication is possibly reduced, protection could be decreased & there are other not-so-nice things. If you use, for example, an 80W145, then the oil at any normal operating temperature will nearly ALWAYS be thicker than if the oil was a 80W90. If you wish to think about this in a different way, imagine the oil is rated at 80W1500, & 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.
There is a rating called Viscosity Index, which is the rate of viscosity (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 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 80W90 GL5 gear oil, with a reasonable range of viscosity index. 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 the best, over-all, although I might add 75W90.
Any oil needs to be of a type that has 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.
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.
If your Airhead transmission is stuck in gear, or neutral; will not shift into another gear; the lever seems disconnected inside the transmission, & you have a shift lever (at the transmission itself), that has a Allen screw in its center...be SURE that screw is moderately tight because if the screw backs out, the lever will move & do nothing!
Transmission rattling noises:
It is NORMAL for Airheads to have the gearbox rattle some when the oil is hot, especially at idle rpm. Usually there is no rattle with cold thick oil. Old Airheads were pretty noisy. Worse as various bits & pieces wear. It is not any problem, USUALLY. The rattle 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
can cause irregular power pulses, primarily but not exclusively from irregular ignition timing. Worn sprockets, worn chain, worn guides and worn tensioner, can all cause ignition timing irregularities. 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 & 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 Airhead engine was at idle. UNfortunately, trying to idle the engine so low (many would try for 500 or 600 rpm, let alone 800), is 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 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, 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; at least early-on.
Transmission problems, checks, testing:
Drain the transmission oil after a ride, when the oil is hot (let the engine and transmission cool maybe 1/2 to 3/4 hour before draining, otherwise the oil may burn you). 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.
FOUR common things that are not usually a transmission-failing problem:
(1) Small/modest amounts of 'fuzz' on the magnetic drain plug, seen at every scheduled (10K-20K?) gear oil change. The fuzz will NOT have sharp particles. The fuzz is paste-like, & smooth feeling.
(2) Rattling noise from gearbox in neutral, at idle rpm, after thorough warm-up, clutch lever NOT pulled in at the handlebars. Noise disappears with bars clutch lever pulled rearwards.
(3) Shifting problems, especially from 2nd gear downward to 1st. This usually means that your input splines need lubrication (unplated early shafts tend to need cleaning & lubrication at 12,000 to 20,000 mile intervals, nickel plated shafts at maybe 20,000 to 35,000 mile intervals)....depending on riding conditions, number of heat/cool cycles, time (in years?) & lubricant used.
(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.
For the major problem, the circlip-less transmissions, the most important on-road indication of a SERIOUS problem that you may have is sudden VIBRATION....& possibly noises. If you feel an unusual vibration, & it need NOT be suddenly extreme at all, not even overly strong at all,....>> and you determine that it is transmission related (pull in the clutch while riding...and ALSO at a stop, engine running....try in gear & also in neutral); That is the time to stop, right then, & 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; and, you risk the entire rear of the motorcycle drive locking-up.
If you do regular checks on the magnetic drain plug (what?...you don't have a magnetic
one???)....you are much less likely to have such sudden problems.
If your transmission is in the range of the circlip-less ones (detailed information later in this article), you might 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. However, if you watch the transmission as FULLY outlined, you can also seriously consider NOT doing a preventative overhaul. Even if you hear & feel nothing peculiar; every few thousand miles, put the bike on the center-stand, when the engine & transmission are thoroughly warmed up from a ride. With engine off, and transmission in neutral, spin the rear wheel & listen for growly sounds. Turn the wheel slowly & feel for notchiness. When the engine & transmission have cooled overnight, check the drain plug. GENERALLY the degradation is slow, but sometimes it DOES come on suddenly, noises and/or vibration. Some remove the drain plug and instead of draining and later replacing the same oil, they have a rubber or cork plug, so the drain plug can be inspected and replaced with very little oil loss. Others check the magnetic plug only at normal transmission oil change time (10,000 miles??). It's up to YOU.
BMW, like most manufacturing companies, is tight-lipped regarding engineering details/changes. BMW tends to be more tight-lipped than many companies, probably from both a corporate policy & the Germanic 'WE don't have problems'. BMW may issue Service Bulletins of various sorts now & then, but these often do NOT spell out details that one might like to have, & 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". In some instances I have been given information that might be considered Company Top Secret. I can NOT divulge in such circumstances my source(s) ...BUT!!.....one way or the other, in almost every instance, I DO manage to get the information to you all.
What are some simple checks & tests you can do to determine if your 5 speed transmission has a problem developing?
(1) AFTER a 15+ mile ride to THOROUGHLY warm up the engine & transmission; on an appropriate stretch of road, in 5th gear, at maybe 5500 rpm (if possible), suddenly whack the throttle wide open. 5th & 5500 is a goodly speed, so you may have to test at lower rpm. If you feel some vibration that is unusual, for SURE you will want to do all the tests below, and in a section much further below.... as the forward bearing on the output shaft may be disintegrating.
A link to a 5-1/2 minute video by Ted Porter (Beemershop.com).
Many folks comprehend better with visual presentations;
after which they are ready for the in-depth explanation.
articles on Anton Largiader's website that you will find of interest, dealing with transmissions. http://largiader.com/ is the HomePage. Anton has two articles to look at, 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 minority opinion for some time now. I DO HAVE those 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 at that time to post his correspondence with me, which I did the majority of, on that LIST. In this 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.|
Many private owners have overhauled their own transmissions, some seemingly quite
successfully, some using information, tools & 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 & specialty knowledge needed to overhaul a
transmission properly so it will last a long time, & with smooth operation. I have put TWO
sections, way down this article, for do it yourself-ers (DIY).
A list of specialists for transmission work:
Brunos, in Canada, has a very good reputation. No personal knowledge, but trustworthy & competent from what I have heard.
Wuma, Inc (Guenther Wuest) email@example.com 6891 W. US Hy 150; Fredericksburg, IN 47120, 812-472-3739. He ALSO does reverse gear conversions (still??) to the 5 speed transmissions; 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 different type of reverse gear conversions
AFAIK, all referenced transmission specialists in this, Snowbum's article you are
reading, can do other types of conversions, such as changing first and/or fifth gear ratios, in 5 speed transmissions)
How to determine if you have one of the possibly troublesome no-circlip transmissions?
Transmissions beginning with serial 240765 SUPPOSEDLY had the circlip re-installed. DO NOT DEPEND ON BMW's BULLETIN INFORMATION USING THAT SERIAL NUMBER!!
NOTE as said at this article's beginning, some 5th gear movement has been seen now
& then... even with a circlip installed.
Summing up to this point: ...it is possible for a transmission built from PERHAPS LATE 1984 (& possibly somewhat earlier), & 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. I have had reports of transmissions AFTER that 240765 NOT having the groove nor the circlip!!...and any I have definitive information on are listed well below. THUS, BMW's own use, in bulletins, of 240765, is NOT to be relied upon.
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. Note that 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, for instance, even a build date as early as September, to be included in the following year's models...and, there is occasionally an anomaly & an 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.
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.
NOTE 2: BMW has had fun & games with transmission serial numbers. It is possible that early transmissions WITH kickstarters had ZSA serials, for one example.
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., is posted to this article in this section,
withOUT identifying the owners name or the overhauler's name.
Effective January 10th, 2016, I want to receive ONLY information on 1983-1985; & 1994-1995 transmissions.
I am interested in those years of motorcycles 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. 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
((There have been NO motorcycles reported, that were built in calendar year 1983, with NO circlip)).
(1) R100RT, USA model, transmission Z094331, VIN WB1044904E6243388. This bike was reported to me as HAVING the circlip (& the wire clip at it). The VIN identification shows it to be a 1984 USA model, but it was built June 15th, 1983. This dating anomaly is not uncommon for 1983-1984 bikes.
(3) 1984 motorcycles:
1990 R100RT, transmission 0180939AAB, VIN WB1046902L6293473, production 04/1990
1990 R100GSPD, transmission 0174962AA1, VIN WB1047902L6134300, production 09/1989, no circlip, 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 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
Viewpoints on the circlip 'problem':
#1: This is the much more commonly accepted viewpoint & I personally agree with it:
The front gear teeth on the output shaft is manufactured on an angle, that is, the gear is HELICAL cut. Its mate is also be that same angle. Picture in your mind such a pair of helical meshing gears. If power is fed to ONE, then the other has forces 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.
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.
Prior to the change in what I think was probably, MOSTLY, 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, & 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 alongside one end of the bearing, more on that later.
When the circlip is left out, 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. 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). 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:
This point of view is quite different. I do NOT agree with it. This view is that while the helical cut gear does move forward under load, it presses the inner race of the bearing, & it takes that load OK 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 & the bearing always takes the axial load, & 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 problem....and....there 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, & 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. The folks who believed in this theory agreed that the clip removal coincided with the increased bearing failures....but say that the increased failures are NOT caused by the clip removal; rather, it was coincidental with the Paralever introduction. They say that the GS Paralever introduction, with its extra travel, puts forward thrust into the gearbox, & even an angular thrust due to the changed design (dual travel angles of the Paralever), & that said angular thrust is taken up by that large 6403 bearing.....& 'proof' is that no extra large REAR bearing was installed by the manufacturer. Thus, these folks believed EXTERNAL forces are the cause for the gearbox failures; they tend to blame too high spring preloads & poor lubrication on the splines. They feel that BMW put the circlip method back into production as it was cheap to do, & 'showed' that BMW 'did something'.
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.
Regarding the 'special 6403-C3 bearing' for the front of the output shaft:
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 bearings, etc.
Below is the 'improved' bearing, SAME part number, note the TM on the bearing.
Here is an EDITED (by me) query & reply, as was on the Airheads LIST in November 2004, that will explain about one thing 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.
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 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.
The throwout bearing area:
This is being put into this transmission article (it is expanded upon here:
due to the potential for someone to think that the transmission itself has a problem. Typically, the clutch will start to slip, when the transmission gets fully warmed from riding. Another symptom is that the clutch seems to be frozen. This is a very different thing from the clutch disc freezing to the plate, as sometimes happens in humid climates, and is described in the clutch article ....and how to fix the problem.
Some tolerances on some transmissions throwout area bore sizes, & throwout pistons, were not held tightly enough, for over the normal operating temperature range. 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!, rarely cold) may stick. Measure the piston, & 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 & fast rule here, but if yours is up to 1.141 or so, I would certainly see how it fits, & 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, & if it looks bad, replace it. Grease it with a good LIGHT non-synthetic grease (NO moly). The reason to use light grease is that it takes time & miles for the transmission OIL to reach this throw-out bearing. Oil the outside of the piston as you assemble this area. Clean & lubricate the arm & associated parts. BMW has a replacement piston 23-13-1-464-167 which is pricey as it includes the bearing & 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:The original piston is not a one-piece metal part, rather, it is a part-metal-colored-plastic-piston item (many were made with the piston being aluminum), & it expands much faster than the surrounding aluminum alloy casting hole (whose tolerance seems to vary), so common 'feel' for clearances may end up leaving it too tight. The updated part fits directly, no problems (probably; but I have had TWO reports of them grabbing....).....you measure & decide. I sometimes test the fit with the transmission at operating temperature. I personally don't bother purchasing the new style, I just do what is needed with the original.
NOTE:There is much more extensive information on the clutch throwout bearing and the lever, etc., here: http://bmwmotorcycletech.info/clutch.htm. That article has a photo of the later style clutch throwout parts, the actuating rod, & notes on the FELT on the pre-1981 rods, ETC.
NOTE: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:
For the Paralever bikes, it is more work:
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 to get all the drilled metal pieces into the vacuum cleaner, not the transmission. 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 "stuff":
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, 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 maybe 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...rare...about .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.
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. However, the 1974 transmission is a special instance. This was a transition year for BMW, from the /5 to the /6; 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 & use of the kickstarter is NOT recommended. There were problems in positively locating the Neutral position, & that wasn't fixed until later. 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 that...in general, 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; 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, wasn't perfectly at 90 degrees. One dog carried nearly all the load; broke off, then another might break. Ask about this if confused & 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 & a late transmission (either direction). Here are some basics:
1. You can substitute directly 4 speed & 5 speed transmissions up to the different clutch models that came out in 1980-1981. Problems will be minor for the 4 & early 5 speed substitution.
2. To install an early 5 speed transmission into a 1981 & 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 shorten the input shaft spline length on earlier transmissions, to fit the 1981 & later clutch. See #8, well below, in the next section of this article.
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 & then use it in an earlier bike. That gets complicated, you need the input shaft, the rear cover, shift parts, input shaft gear, ETC.
5. The best method, & cheapest, of putting a later (1980/81+) 5 speed transmission into an earlier bike, is probably to install the later clutch & clutch carrier. That means that from flywheel back, you install all the later items. Direct fit. I highly recommend you do NOT use the 1981 clutch items, unless they were updated (the 1981 was weak; could disintegrate)...see my clutch article: http://bmwmotorcycletech.info/clutch.htm. It is possible a very few 1980 models had the 1981 poor clutch.
Here's more information on a variety of transmission things:
1.http://www.largiader.com/tech/airtrans/. 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 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 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.
If you have a non-Paralever model, and oil is transferring from driveshaft to transmission, you probably 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. 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.
4. There are quite a few 'tricks' & 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.
6. 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 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. The OFFSET segment for pawl spring clearance was one such change. Several changes occurred at that same time at serial Z5A79720.
There are DOZENS of these 'nice to know', or 'NEEDED to know' items.
7.The /6 kickstarters should not 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 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. This ensures proper engagement. Release the clutch lever. KICK.
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 apply blue Loctite-applied to the added screw and use a large washer. Information and a photo are well below in this article.
10. Shift kit and pawl spring, etc:
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. Theserial number for the beginning of the shift kit installation is: 56477. The prefix was Z or ZSA. Frankly, I do not trust that serial number.
The purpose of the shift kit was to eliminate false neutrals or hung-up shifting; 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. The shift kit 'fixes' for false neutrals do not have the same level of improvement in the heavy flywheel models as the later clutch carrier models.
In the September 2003 issue of BMW Owners News, from page 34, is an ILLUSTRATED article on replacing a broken Pawl 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 relieved to be sure the spring does not bind up & break again! In the November 2003 issue of BMW Owners News, from page 34, is an article on installing the updated shift kit. There are some errors in the article:
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, 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 available parts:
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?
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 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. Since the diode is under hardly any stress at all, this situation would be VERY VERY
12.The 4 speed transmission & early 5 speed transmissions can be difficult to find parts for, & very 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.
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 anduse 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 & 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.
18. 1981 & later models have a lipped seal at the rear cover, it is not easily replaced....the transmission must come apart. Install the pushrod on these models 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 inch).
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.
Read the early part of (way up this article):
4-speed transmission modification that I recommend:
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. Keep your bike metric. Thread the hole, 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.
4 speed transmission:
5 speed transmission:
RE: 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, what can & cannot substitute & what won't fit, etc.
Below is link to a website page that tells you how to overhaul your 5 speed transmission yourself.
see also: MORE DISCUSSION an area very far up this article.
This link was given to me; 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.htm, then click for gearbox.
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.
DYI (Doing It Yourself) (part 1)
If you insist on overhauling your own 5 speed transmission, understand that there are a lot of big and little things to know; and I have tried to put nearly all of those things into this very long article. Many HAVE done an overhaul successfully (usually not a full overhaul); and whilst the overhaul might not be up to 'Guru' standards, it can be adequate. I have greatly resisted pressure to do step by step transmission overhaul articles, because of all the little details, which vary by model and year and serial number of transmission and what you find inside. On the other hand, I do wish to have something for you to look at. So, I offer the following TWO URLs:
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 machine work, had LOTS of tools (and some parts) for everything from the Isetta cars, through the /2 era, up until the Airheads stopped production in the 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 www.cycleworks.net. Dan will likely be very helpful.
DYI (Doing It Yourself) (part 2):
This next-following 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 & a couple of miss-spellings and grammar corrections and a note or two from me. My purpose in putting this posting here is to give you more of a feel for 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.
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 in that. Transmission spline lubrication is covered elsewhere's on this website, in article #43. Establish the proper interval for YOUR bike, YOUR riding habits.
4 speed transmission shift fork bolts: 17 foot-pounds
Revisions: (updates for bike serial numbers, transmission ID & VIN updates are not usually listed here as a Revision)
07/07/2008: all prior updates incorporated & minor editing for clarity; including 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.
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 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.
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