I was in the process of removing the rear drive so I could grease the splines on my 1985 K100RT.  As I removed the drive assembly, the drive shaft came with it.  The shaft was a little stuck on the rear drive splines but with a small tap of a rubber hammer the shaft came right off.  I cleaned the drive and shaft splines and they look nice on both ends.  It only has 30,000 miles but does not appear to have ever been lubed previously.   The problem is the u joint is a little notchy when moved up and down, either direction, so I would like to replace the u joint.  I looked in my Haynes and Clymer manuals but neither has any info on u joint replacement.  I looked on a couple of the BMW web sites for parts and don't see the u joint listed as an available part, only the drive shaft assembly.  In searching the K100 forum I did find one topic on this saying the u joint is replaceable, but does not have C clips holding it in like is typical with cars.  Rather, the u joint is staked in.  I guess my question is has any one replaced their u joint and where do I get parts.  Thanks,

Jim

Try doing a search on local shops that do drive shaft service.  I think I have seen some shops posted on forums that do u-joint service on beemer shafts, too. 

What would be really cool would be for somebody to offer a c/v joint retrofit.  Then the monolever drive shafts would last forever with no maintenance.

flyinglow wrote:. . . The shaft was a little stuck on the rear drive splines but with a small tap of a rubber hammer the shaft came right off. . . ..

Just to clarify for those who might not be familiar with this critter, the drive shaft wasn't a little stuck on the output shaft splines. It was attached to the output shaft by means of a snap ring located within the drive shaft joint. When the drive shaft is reassembled to the transmission, a rap on the rear end of the drive shaft with a mallet will reattach it onto the output shaft, using the snap ring to lock it into position.

Regarding how the movement of the joint itself feels, I've learned that when a part seems worn, it seems almost perfect when I discover how much it costs to replace it.      If the joint doesn't move forward and rearward or side to side within its yokes, if it were my bike it would be good to go.

Bruno's Machine & Repair
91 Arnold Street
Kitchener, Ontario N2H 6C9
Canada
519 745 7824
brunos@brunos.us

Hi Laitch.  I just saw your reply, thanks.  I did not see any snap ring, as you mentioned, in my u-joint so I just looked again.  I don't see any and don't see any groove for one to be in.  Is it possible some 85's didn't have a snap ring?

If you don't find the clips inside the u-joint, check at the gearbox output shaft.

Two Wheels Better wrote:Bruno's Machine & Repair  

About Bruno....from what one could read on other forums it haven't been so
much activety at the shop during the last couple of years...due to cancer and
a surgery last year.......hope he have a good recovery.

Flyinglow....as you're on the other side of the pond.....search hendersonprecision. CA.

Based on your picture I took a closer look at my u-joint and sure enough there was PART of a C clip in the groove within the joint.  The remainder of the c-clip was laying in the swing arm after I removed it.  Now I know why the drive shaft came out with the rear drive assembly, when I removed it.  Without the full C-clip locked in the U-joint groove, the drive shaft slides on and off the output shaft, without snapping or locking in place.  I ordered a new drive shaft.  If the C-clip wouldn't of failed, I would not have know my U-joint was going bad because I wasn't planning on removing the swing arm and drive shaft.  So, maybe I was kind of lucky.

flyinglow wrote:  Now I know why the drive shaft came out with the rear drive assembly, when I removed it.  Without the full C-clip locked in the U-joint groove, the drive shaft slides on and off the output shaft, without snapping or locking in place.   If the C-clip wouldn't of failed, I would not have know my U-joint was going bad because I wasn't planning on removing the swing arm and drive shaft. 

You indicated the driveshaft was stuck on the output shaft, not that it came out when you removed the swing arm assembly. You wrote you had to knock it with a mallet a couple of times to release it from the output shaft; maybe that is when the snap ring broke. You could be more brutal than you realize.    Usually the drive shaft can be clamped on the output end with a vice-grip and the pliers pried or knocked to release it from the output shaft. 

When a u-joint fails, it might signal the impending outcome in a couple of ways—a persistent beat felt through the seat while riding that increases with engine speed, or by a noisy disintegration followed by a generally ungraceful stop, while riding. It hasn't seemed to disintegrate, and you haven't mentioned experiencing any other indication.

Anyway, now you will have a new one to install and will be bathed in the state of grace that newness always provides. You can then refocus on getting your bike to run when you're finished,  and defending your life in traffic when it eventually does.