Driveshaft

[Beemervet]

What year had the first "cushioned" driveshaft? I'd like to upgrade my '77 R100S. Thanks

[20774]

Looks like they were introduced in September 1980.

http://www.realoem.com/bmw/showparts.do?model=0437&mospid=47886&btnr=26_0114&hg=26&fg=05

Kurt in S.A.

[PHMarvin]

Hi, Beemervet,
I disagree with Kurt. According to my parts book (4/84), the cushioned driveshaft first appeared on the '79 model year bikes. My guess would be bikes produced starting 9/78 would have the cush drive; those produced 8/78 and earlier would have the solid driveshaft.

[20774]

I was going by the on-line parts lists...I don't have much experience with this kind of driveshaft. I have '78 /7. I did managed to find this input from Ted Porter on the Airheads lists when someone asked the same question:

"Cush drive driveshafts for twin shock bikes were used 1979 through 1984.
However if you try to install a used 1981-84 driveshaft into a 1979 or 1980
swingarm it won't fit. The 79-80 swingarms are smaller internally, the 79-80
cush drive driveshafts have two flats machined into the spring base that
allow it to slide into the smaller swingarm. The 81-84 cush drive
driveshafts don't have these flats but they can be machined into the shaft
if you know what you're doing.

There is a part number for a retrofit cush drive driveshaft kit that will
fit the smaller swingarms used from 1973 1/2 through 1980 which is part
number 26 11 9 055 059.

If you want to install a cush drive driveshaft into a late 73 through 1978
model, or if you want to replace a 1979-1980 cush drive driveshaft with a
good used cush drive driveshaft, it must be from a 1979 or 1980 donor bike,
or you must modify it as described above.

You can install a NON cush drive driveshaft from any late 73 through 1978
model into the 79-84 models.

R65 models don't apply to these comments of course because they have their
own shorter driveshafts.

The R80ST and R80G/S use the same cush drive driveshaft as the other full
size 81-84 models.

The cush drive does make the bike shift better, but it does add some
driveline lash. Some folks like it, some don't. I installed one on my 78 and
I like it."

Kurt in S.A.

[Beemervet]

Would'nt substituting a complete swingarm w/ cush driveshaft work? That would eliminate having to extract the driveshaft and reinstalling it into the old one.

[PHMarvin]

Hi, Beemervet,
Thanks to Kurt for his last message. I'd forgotten that, in fact, the swingarms changed between the '80 and '81 model years. And, although I knew the driveshafts changed to the cush drive pre-'81, I didn't realize the later driveshafts wouldn't fit into the earlier swingarms without being machined. Thanks again, Kurt, for remembering and bringing this up.

As to Beemervet's question, yes, switching out the swingarm to the later model would work. However, if you use wider (120/90x18) tires on the rear, you have a little more clearance with the earlier swingarm than with the newer one. It's your choice, though. I've had 2 airheads with the solid driveshaft ('76 R90/6 and '77 R75/7) and 5 with the cush drive and, frankly, I never noticed the difference. YMMV.

[20774]

Thanks again, Kurt, for remembering and bringing this up.

Well, don't give me too much credit. Frankly, I don't remember much these days, but sometimes I'm pretty good about searching for what others remember. :)

Kurt in S.A.