Transmission Input Spline Cleaning, Lubrication, Hints

Applicability: All BMW Airhead models; with some useful information for any splines-driven dry-plate clutch.

Why do it: (1) Smoother shifting; (2) Avoid wearing out expensive parts with expensive labor to repair damage; (3) Avoid suddenly spline failure

When to do it: Depends on year model and conditions you ride in, but probably every 12000 to 35000 miles.

What are you going to do: Unfasten the transmission, move it slightly backwards, clean and lubricate the transmission input shaft splines, and then reinstall transmission. You will probably do other work at the same time, described in the text that follows.

NOTE:  While an adequate job can be done by just moving the transmission backwards, a 100% job means removing the transmission from the motorcycle.  THAT can be put off until you have another reason for removing the transmission.

Required Skill level: Lower intermediate or better

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Throwout Bearing Maintenance

…cleaning, inspecting, and servicing the throwout assembly on ’74 to ’84 airheads every 10K. Would someone be willing to describe this process in enough detail so that I would have half a chance of performing this myself successfully?

Sure… The reason I suggest doing this, is due to the nature of the layout of the rollers in the bearing. Before the ’74’s (/5 and earlier), BMW used a ball bearing throw-out assembly. They went back to this after 1984. If you referrence a price list, you will see that the ’74 to’84 roller set up is a LOT cheaper. The rollors are laid out radially in a circle.This insure that as the rollers attempt to roll, one end will go faster than the other and will scrape on the two “thrust pieces” on each side.

The bearings do fail (usually indicated by a sudden need to take up slack in the clutch cable). Now, the failed bearing, the two thrust pieces and the clutch thrust rod are turning as a unit. The clutch end of the thrust rod can bore into the forward pressure plate of the clutch assembly. Surprisingly, the bike can still be operated while this is going on, with the rider noting strange shifting and odd clutch noises. This happens often enough that I carry a spare set up as insurance for my wife’s ’78 R100/7, when we tour. (I have, of course, the vastly superior /5)

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Spline lubricants

Airheads need scheduled lubrication on transmission input shaft splines (never grease the clutch disc splines themselves); and, rear wheel cup splines and associated rear drive output splines on the twin-rear-shock models.

Numerous lubricants have been tried in many different climatic and riding conditions, over many years.  Some newer lubricants are still being tested.  There does not seem to be any magic, perfect lubricant for these places. BMW has specified quite a few lubricants over the years, such as Staburags, Optimoly, ETC.  The author has never believed these lubricants were as good as some others, at the times BMW had those recommendations.  The author, and others, have done long-term testing on various lubricants.  This article you are reading no longer lists these lubricants, nor recommended lubricants, as the latest information will be found HERE:
http://bmwmotorcycletech.info/chemicalsetc.htm where the author keeps the information up-to-date.  The spline lubricant information is at item #6A in that article.

Later model (exact year and models are unclear, probably late 1980’s) transmission input splines are SUPPOSEDLY nickel-plated and do not require cleaning and relubrication quite as often, but 30,000 miles seems the practical LIMIT, and for earlier ones perhaps 20,000 is the limit. Best you do it before these mileages, at least once, and then, upon inspection, adjust the interval for the next clean/lube.   Once a spline shows rusting, you are LOSING METAL! The transmission input splines are fine-pitch and not very deep….you do NOT want them to fail!

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Re-Gearing an R80/7

Charles Bachmann, charles_bachmann@mgv.com writes:

Hi Airheads,

I am a fairly new owner of a 1978 R80/7. It is a great, fun bike. However, I find that at speeds over about 60 mph, the thing turns higher rpm’s than I would like. I am considering going to a higher gearing.

Thanks for any feedback/advice!

Charles Bachmann
Raleigh, NC

I know how you feel. I’ll bet you’re always looking for 6th gear.

A 37/11 drive is the same that came on my ’74 R60/6. At 60 mph I’m showing at least 4000 rpm. Kinda high. But it’s only a R60. On the other hand, it’s the same drive that came on my ’83 R80RT. This was not acceptable to me. I replaced the 37/11(3.36:1) with the next higher-up 32/10 (3.20:1) from an R75/5. The drive housing has a different look & design, but everything fits fine. It was better, but still too revvy for me. Unlike you though, the ’83 R80 has lower compression than your ’78, therefore less horsepower too. I dare not try a higher drive because I have already lost a fair chunk of power.

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Transmission Mainshaft Circlip Install

If you ride an airhead BMW made between 1984 and 1995 your transmission may be on its way to lunch. That’s because sometime in 1984, BMW decided to stop installing a circlip on the transmission main shaft. The circlip keeps the bearing next to it from moving axially on the shaft, putting axial loads on said bearing. The walking is induced by axial loads imparted to the shaft from the helically cut gear that drives the shaft from the input shaft of the transmission. Ball bearings really don’t like axial loads, and often show their displeasure by shedding the cage that keeps the balls separated. When the cage pieces fall out of the bearing inside the tranny they can become lodged in other bearings or between gear teeth, and the tranny quickly quits transmitting power. Frequently it locks up, leaving the rider skidding down the highway and stranded at the side of the road. In the winter of 2006 I started looking forward to a Spring trip to Baja, Mexico, and the thought of this ticking time bomb inside my bike started to really chew on my conscience. I’d never seen anything other than fine flour deposits on the tranny magnetic drain plug during oil changes, so I was pretty sure there wasn’t anything drastically wrong with the box. Even though some bikes made in 1993 did have circlips (that is the transition year when BMW came to its senses and started re-installing the circlips, possibly starting with gearbox number 240765) I knew this one didn’t because I’d seen it missing when Dave Gardner upgraded first and fifth gear a few years before. He didn’t have the equipment to machine a new groove into the mainshaft, and said it was nothing to worry about anyway as he’d never seen a bike with the problem. Never the less visions of being stranded along some desolate Baja dirt track motivated me to start looking for some help in getting the potential problem defused. Ted Porter works out of his BeemerShop in Scotts Valley, California, a mere sixty or so miles from my home, and it didn’t take long for an email inquiry about the job to be answered in a very positive and professional manner. I pulled the transmission out of the bike (only took an hour or so) later that week and had it down to Ted that Saturday.

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Airhead Transmission Ratio Swap

In early 2002 I learned that it was possible to change the ratios of both first and fifth gears in the GS transmission by swapping out gears. Surprisingly, only one of the gears of the respective pairs need be changed. I called Cal BMW and Ozzie’s BMW for pricing, and found that each wanted almost $300 per gear for the parts, plus labor to do the swap. That was prohibitively expensive,and the idea went onto the back burner. Several months later I was leafing through the back pages of a Classic Bike magazine Gene had loaned me (it was the issue that profiled Norton’s Production Road Racer from the ’70s), and I noticed an advertisement from S. Meyer in Hillesheim, Germany advertising BMW parts. Having previously dealt with many parts suppliers in Great Britain, I composed an email to S. Meyer inquiring about the gear swap.

In a few days I received a reply quoting the following prices:

6 % lower 1st gear Euro 90
18 % lower 1st gear (Set 2 gears) Euro 250
6 % quicker 5st gear Euro 120
10 % quicker 5st gear (Set 3 gears) Euro 620

At the time, a Euro was going for about $.95, so these prices represented a vast departure from what was being quoted locally. The gears were made by a company called Kaiser. I FAXed a copy of my Visa charge number along with a note explaining what I required (6% lower 1st gear and 6% quicker 5th gear) and in about 3 weeks the parts were sitting on my front porch.

In the mean time, I started local inquiries for someone to do the installation, along with a general reconditioning of the transmission: replace all bearings and bushings, replace shifter spring (prone to breakage), etc. One of my buddies suggested I call Bob Grauer, who seemed quite knowledgeable and willing to undertake the work. I told Bob the parts were on the way, and that I would contact him again when they were in hand. When the gears arrived, I emailed Bob asking when I could bring the transmission by, and he indicated, by reply email, that he was no longer interested in doing the work. I called him, asking for some elaboration, but all he would say is that he wouldn’t do the job, and that I shouldn’t have any trouble finding someone else. I still have trouble adequately expressing my shock, dismay, and anger at this behavior. Absolutely unprofessional to put it mildly. But enough said.

Gene suggested I try Dave Gardner at Recommended Service, an independent mechanic he’d been using for years for tires and, more importantly, transmission work. Dave was interested, but was concerned about the quality of the parts until I mentioned they were sourced from S. Meyer. Dave was familiar with the company, explaining that they had partnered with BMW in the ’40s, ’50s, and ’60s to assemble some of the most successful race bikes in the company’s history. We set a date for the next Friday, and I got busy pulling the transmission from the GS.

I won’t go into the removal process here, except to say that it was very nice that BMW uses the frame to support the center stand on the GS, and unlike the K series, it isn’t necessary to rig up some sort of auxiliary support for the rear of the bike when pulling the tranny. The job went very smoothly, and after three or so hours I had the transmission on the bench. I hate working on dirty parts, and I figured Dave would appreciate getting a clean transmission case. I Gunked it, first sealing off the speedo drive hole with duct tape. After drying, I went after the corrosion on the top (where the air box sits) with a brass brush and contact cleaner. It never did get to silver white, but the crusty white deposits were removed.

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Throwout Bearing Maintenance

Sure… The reason I suggest doing this, is due to the nature of the layout of the rollers in the bearing. Before the ’74’s (/5 and earlier), BMW used a ball bearing throw-out assembly. They went back to this after 1984. If you referrence a price list, you will see that the ’74 to’84 roller set up is a LOT cheaper. The rollors are laid out radially in a circle.This insure that as the rollers attempt to roll, one end will go faster than the other and will scrape on the two “thrust pieces” on each side.

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