It is a rare occasion that an episode from the garage makes it into the main blog, however this is a worthy exception. It is a tale of good fortune, of divine intervention, and of impeccable timing. The tale begins with our intrepid hero in Frenchtown NJ, on the way back from the Norton Gathering, on a beautiful spring morning, on the relatively new-to-him R100GS. He noticed a slight vibration in the rear wheel between 60 and 65 MPH. It disappeared above or below that small range. The classic diagnosis is that one of the stick-on wheel weights had gained its freedom, or that the spoked wheel needed truing. No big deal. He continued home at a sedate pace enjoying the emerging greenery that is spring in the northeast.
Back at the bat cave, our hero got the bike on the centerstand and looked at the rear wheel. Running his hand around the spokes did not uncover loose or broken ones. The wheel did have an area with some old tape from wheel weights, but it was hard to tell if it was recently disturbed, due to dirt. His memory was of no help. He then grabbed the wheel and tested for vertical and horizontal play. Rock solid. Now if you know the BMW airheads, you know that the good news so far is not necessarily good news at all. A loose lug nut or a broken spoke would actually spell relief. The forums are littered with tales of final drive failures and universal joint failures at 30,000 to 40,000 miles. Mine had 46,000.
With the bike in gear, he rocked the wheel backward and forwards. There was certainly some play before the transmission engaged. Not good. Then he performed the acid test which spun the wheel backward in neutral. He could clearly hear the dreaded clicking sound that said driveshaft/u-joint failure....At this point, there are generally two options. The first is to sit down, mix a stiff drink, and weep openly. The second is to sit down, mix a stiff drink and celebrate the fact that it does not appear to be your transmission, then weep openly.
If you have no interest in the how-to section of this post, take the bypass as indicated below and join us later..
BYPASS-READERS, EXIT HERE
He began the teardown shortly afterward. 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 looked fine only days before, so either he 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. He 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, he would have been putting a new shaft in with lovely new grease and lots of little pieces of metal ! He grabbed a beverage, sat down, considered the bits of motorcycle all around him, and gave thanks.
BYPASS-READERS, RE-ENTER HERE
A week later, he 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, our hero 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 he was determined not to buy another costly use-it-once-every-five-years BMW tool.
While the bike was laid up, he 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. He gave 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. Our hero may just get some robes and a pulpit, and turn the garage into the center for repair, intervention, and maintenance early (CRIME).