Here are a few pic's from a FD that had been rebuilt twice at different dealers. The first rebuild failed at 7,000 miles & this one failed at 35,000 miles. This is the first seal cover I have had to replace in over 30 rebuilds that I have done. The bearing on this rebuild had three balls that were split in half.

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My word - I've seen some toasted final drive bearings in my 13 years around these parts, and that one is the worst one I've seen, Dave. Can't imagine how many miles were ridden following the initial damage. You replacing any of the other related components?

The parts for this rebuild were: Crown bearing, Crown bearing shim, Crown bearing seal Crown bearing-seal cover, & one pivot pin bearing. I also had to remove the pinion assembly & reseat the pinion needle bearing sleeve with Locktite.

Classic side load induced failure of a ball bearing Dave. Obviously reassembled rather than set up I suspect. Of course you'll never know now, but it would be interesting to know by how much that 1 was over-shimmed by. If you don't mind me asking, what sealant do you guys use on the pinion nut threads ? I am contemplating using Loctite 567 teflon thread sealant. It seals well in oil but never sets and can always be undone. Doesn't set the same as the other (anearobic curing) types.

For the pinion nut I use Loctite red 2760 fast curing for fasteners up to 3/4".

For the threaded seal ring nut I use Hylomar Universal Blue Racing Formula.

The Aussi is right........! BTDT

Hiya Dave,

Are you documenting the existing shim(s) thickness and comparing that to what you measure for in your new setup?

That's how I got my data suggesting that the cause of the crown wheel bearing failures was excess shim thickness. It would be nice to continue to add to that information.

I watched a BMW mechanic "rebuild" a FD without removing it from the bike. New crown bearing. reassemble, refill, done. 'Nuff said.

Also looks like someone was in there with a pipe wrench and wood chisel.

What I have found in rebuilding FD's that are still in good condition is that the new bearing alone can change the preload up to .004". I just finished a preemptive rebuild on a FD that had 55,000 miles & had .003" too much preload. With the new bearing installed it only had .001 too much preload with the factory shim set up. When I took the bearing apart it showed no signs of wear. It did not have the nice polished surface that I have seen on bearings with over 100,000 miles that had the proper preload.

All of the failed FD's that I have done had at least .004" too much preload with a new bearing installed & some had as much as .012". I don't check the preload on a failed bearing before I disassemble it. I aim at a preload of .003" & I have enough shims to achieve that within a half of a thousands (.0005) on each side of .003".

So far I have never had a FD under shimmed or even on the low limit of the spec.. Of the nine that I have done so far this year five had the creeping needle bearing sleeve.

This FD was definitely damaged in shipping..... It certainly could not have been that bad when it was removed from the bike.

Nope this was not a UPS (United Package Smashers ) or any of the other shipping Co's. This FD was hand delivered to me. This was the third time it has been rebuilt & who knows how many miles it was rode each time it failed. I did ship the old damaged cover back with the FD because it was too damaged to use for even a short period of time.

I carry a new crown bearing & seal with me when I'm riding out of town so that I can do the same for anyone that needs it done while they are on the road. It does not fix the reason why it failed in the first place but it gets them riding again.

I have now rebuilt two FD's that the dealer just replaced the bearing with the original factory installed preload shims only to have the new bearing fail again at 7000 miles or less.

I have also checked a dealer rebuild that was done on a LT that failed with about 10,000 miles on it from the factory. It had less than 1000 miles since the dealer had rebuilt it & I re shimmed it to spec. & it now has over 40,000 miles on it. This rebuild cost over $1000 from the dealer. It was .010 over shimmed .

Yea Dave, that was the point I was dancing around. As far as I can see it's impossible to properly rebuild a FD on the bike. It's the equivalent of fix-a-flat in a can but I bet the owner got charged for a full rebuild. That's why mine went to Curtis when it crapped out. I would trust you, Curtis, John, and maybe a couple others who I've forgotten to do it right. Dealership? No. Not unless I was watching them in person.

Definition of insanity - continuing to do the same thing and expecting a different result. The fact that any dealer would just rebuild a FD unit without performing the set-up procedure indicates they do not understand the problem in the first place. The fact that some here have learned to rebuild the FD's properly, with very reliable post-rebuild performance also tells me that the design is fundamentally sound. Understand the problem, set the units up correctly, tour with confidence

Can you tell me basically what a "set-up" is? Thanks

In the case of the crown wheel 61917 c3 ball bearing failure, it is the shimming process which sets the correct amount of preload for the taper roller bearing on the oposing end of the bevel gear carrier. That preload must not be too great as, in this compact gear drive arrangement, a ball bearing has been employed to carry the radial load, but ball bearings are not designed to sustain high side loads. The is also a required set-up procedure for to ensure correct pinion to gear meshing. This must be done whenever pinion bearings or the taper roller bearing on the bevel gear are replaced, There are literally dozens of posts on this site about the failures and set-up procedures, including video clips etc.

Thanks for the info. Hope I never have to do this to my FD. I'm a do-it-myself type person and it would probably drive me insane.