Transmission – Airheads Beemer Club

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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Throwout Bearing Maintenance

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