Roll-on / roll-off bucking or lurching

[dogshome]

Rear bevel drive.

[Steve]

"Rear bevel drive" sounds like you're talking about the ring gear and pinion. Exposing that would require special tools I don't have. Or are you talking about the straight splines that directly drive the wheel? They are on the outward-facing end of the ring gear, and are visible with the wheel removed.

[dogshome]

Oh no, just the spline that you see when removing the rear wheel.
https://bmwmotorcycletech.info/rearwhlsplines.htm

[Steve]

The final drive splines, the ones that are on the output side of the ring gear with matching splines in the wheel, are about 70% worn out. I'm going to have it fixed by a mechanic I have located. Don't know if it will fix the bucking, though.

[dogshome]

My friend with the flies in his teeth is probably right then. If you only have a third of the spline width left, that could be your problem.

Weld on replacements can be had, but I would look for a used final drive. R65 ones are usually available as most people change the fd. For a higher ratio with engine mods.

If you have a variable speed gun drill, they are very easy to test just sat on a bench.couple up with tape to the input, spin it at a slow speed and listen. I have a vid on YouTube.

[dogshome]

Changing the fd is very simple. If you can take the wheel out, you can do that.