saddleman said:
I disassembled a FD today that was rebuilt recently by someone unknown. The pinion nut had come loose & destroyed the pinion gear. The riders complaint was vibration at 60+ mph. while accelerating. The rider also said that coasting with the clutch lever pulled in the vibration went away. This FD is probably not worth rebuilding.
That is an unusual failure. Torque specifications for the input pinion nut and locking ring are high and a good jig to secure the FD is needed. Also a special tool is needed to secure the crowngear/pinion gear from turning during assembly torquing. It is easy to understand that someone didn't get it right leading to the pinion shaft assembly coming loose over time.
I have always recommended looking for a used FD to rebuild rather that get into rebuilding a FD where the pinion gear/crown gear set needed to be replaced. BMW only sells the pinion gear/crown gear as a set. A mechanical engineer would need to tell me why, but I would be reluctant to combine a pinion gear from one FD with a crown gear from another FD. Were that to be done, the owner of the FD should be informed of the "creative" rebuild and I wouldn't warranty the rebuild. (I would consider doing it for myself but would not send someone else off cross country on such a rebuild.)
The problem with rebuilding a FD from pinion shaft replacement and up is that shimming for gear tooth contact pattern needs to be checked and shimmed, then the tapered roller bearing needs to be shimmed for backlash before moving on to crownwheel bearing shimming. That's a lot of labor, especially if the setup needs to be adjusted by changing shims. That's why it would be very hard to make such a rebuild cost effective, even with used parts. I have always felt that finding a used FD on eBay for a few hundred bucks and rebuilding it was a better option.
That said, Dave, you are the guy to plow new territory. Keep posting, I enjoy seeing your method, and surgically clean work surfaces. :thumb:
