u-joint inspection

Bike: 1978 R100S. I've been checking and reassembling a project bike. I noted a slight knock from the drive train while turning the rear tire by hand or rolling the bike around in the garage. It's a much louder knock while under power and riding slowly.
I disassembled the rear drive train up to the tranny. The rear drive and transmission both turn easily and smoothly by hand. The u-joint however seems to have a bit of "notchiness" on one axis. Is this normal or possibly the source of my knock? Any thoughts would be appreciated.

U-joints are not supposed to knock. Sounds like time for a new driveshaft, or you'll need to remove the old one and get it refurb'd.

If there is any sideways or up and down play in the u joint then it is toast. Sounds like you may need a new one.

One thing to check is that there is proper clearance for the driveshaft too work up & down. A lot of times people get so intent on centering the swingarm they forget to allow a bit of room for the U joint to work properly. Check and see that it is not the driveshaft hitting the tube. If it is a clearance issue you may have to adjust the swingarm by moving it a little to the left or right to fix this problem.

Excellent advice. If I adjust the swing arm slightly to the left the knock goes away. The u-joint was rubbing the inside of the swing arm bell opening. Thanks!

what happened with that notchy u-joint you felt? not notchy, or are you planning to ignore it until it blows apart?

I sent an email inquiry to Ted Porter to see if they rebuild twin shock airhead u-joints. (They don't as they rarely need it) Ted advises a slight notch in the middle of the u-joints travel range as normal. That's what I have. There is no axial or rotational play. So I'm going to go with it.

gotcha.

for those in need of a shaft rebuild.. http://www.machineservice.com/
less costly than Bruno's, and no border issues to deal with.

Or, as recommended by Ted Porter: Henderson Precision, in Big Oak Flat, California.