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1990 BMW R100GS Dakar

U-Break U-Joint U-Fix

Classic Velocity

Note: A longer version of this post can be found in the main blog as Getting the Shaft and other Blessings

The shaft drive of the BMW is a brilliant evolution of a 1920s design. It is sturdy, reliable, and has great benefits over a chain drive. However, the R100GS has gathered a reputation for being hard on u-joints. Some say it is the more acute angles of the shaft required for the GS, some say aftermarket shocks, some say sun spots. Regardless, they have a high failure rate on these bikes, and examination of the shaft every rear tire change is recommended. The front driveshaft u-joint on my bike looked fine only days before, so either I missed seeing a crack, or it went from good to no good during the ride.



With the driveshaft out of the swingarm, the level of his good fortune was obvious. This was the original shaft, and while the rear u-joint was fine, the front had two damaged pivots. The housing was broken, and needle bearings had escaped in every direction like some disturbed ants nest. The amount of play in the joint was excessive. I realized that he could not have been more than a few miles (or a few ft/lbs of torque) away from complete disintegration, or lockup, or some other less than desirable outcome. This was close. Really close. Inside the swingarm were the pieces of the housing and needle bearings. Without cleaning it out thoroughly, I would have been putting a new shaft in with lovely new grease and lots of little pieces of metal ! I grabbed a beverage, sat down, considered the bits of motorcycle all around me, and gave thanks.

 

 

 

 

A week later, I had a new shaft with circlip equipped u-joints so they are now replaceable. It also has grease nipples, so it is serviceable. Thanks to Bruno's in Canada for the new shaft. The installation was almost a breeze, just pay attention to a few caveats, and reverse the process. Torquing the front driveshaft bolts is a pain without the proper tool. Taking inspiration from online forums, I used a ring spanner with a socket stuffed in the other end and a torque wrench. A bit imprecise, and sure the BMW tool is perfect for the job, but I was determined not to buy another costly use-it-once-every-five-years BMW tool.

While the bike was laid up, I dropped the pan, and removed both petcocks to find both of the reserve tubes clogged ! That would have been a surprise discovered at the worst possible time and place. Igave thanks for that as well. In fact, this whole philosophy of being thankful for the discovery of problems and narrowly avoided disasters, seems well-suited to classic vehicles......