Rear drive stiffness / binding

[jimmyC86]

1984 R80RT....Hey guys - I just finished fully rebuilding the rear drive. Cleaned, new seals, gaskets etc. Everything lined up very nicely, teeth engaging smoothly. When I placed the drive cover on (without tightening the 8 bolts) I could hand-turn the pinion to engage and spin the final drive (part that sits in the wheel hub). However as soon as I tightened and torqued the 8 cover bolts, it became very difficult to hand turn (either from the pinion or the final final wheel hub portion). Something tells me it should move relatively easily, but want to check with the pros before I disassemble again
Thanks

[Kurt in S.A.]

What's the process for shimming and determining preload on the final drive? Seems like I'd investigate that area.

Kurt in S.A.

[jimmyC86]

Yeah that’s what I’m planning on jumping into. I just reused all the same shims that were in there but suspect I’m going to need more of this isn’t normal. My first BMW and picked it up not running so who knows what errors were made previously

[Rob Frankham]

Sounds like a 'shimming' issue if ever I heard one...

Playing around with a bevel drive is a lot more involved than it seems. Clearances are critical and whenever you dismantle the drive, you need to check and adjust them. Failure to do so can result in stiffness, excessive wear, excessive backlash in the drive chain and/or noise from the drive. This is the reason why Haynes doesn't even go there stating 'Dismantling the drive is beyond the scope of the majority of amateur mechanics'. Clymer, however, does give a fairly good and understandable description of the procedure.

Sadly, I have to say that, unless you are willing to read up on and follow the procedure for re-shimming both the crown wheel and the pinion, get the special tools and do a very painstaking job, you would be well advised to take the drive to a reliable workshop for reassembly.

There are very few parts of an airhead I wouldn't willingly work on but I tend to leave final drives well alone unless there's obviously something wrong. Fortunately, as long as they're looked after, they're pretty bulletproof.

Rob

[jimmyC86]

Well...Oops! Thank you for the guidance. First BMW but have restored several bikes. And as always, as soon as it seems things are moving right along...there is always a grand challenge.

[Kurt in S.A.]

This might provide some insight on what's required:

https://www.youtube.com/watch?v=9rw6IQcBnXQ

Kurt in S.A.

[Rob Frankham]

This might provide some insight on what's required:

https://www.youtube.com/watch?v=9rw6IQcBnXQ

Kurt in S.A.

Very good... I do like Williams videos... but... he still doesn't mention checking clearances. It should be done every time the drive is opened...

Rob

[jimmyC86]

Thanks guys - I had watched that video and while a good overview - as Rob states it doesn’t go into clearance/shimming process. I did find a video that covers it in more depth, how to find the measurement without the BMW tools. But for starters, I tried tightening the cover with no shims in...even once without the thrust washer as well. Interestingly it still binds. I thought possibly it was the bearing improperly seating in the cover so I seated the bearing/ring gear first and then installed. Same thing. Seems there is something else occurring

[Rob Frankham]

Does the pinion turn without resistance when the crown wheel isn't present? I guess that's the case from earlier posts. My next move would be to remove the pinion and reassemble with just the crown wheel to see if that turns freely... if it does, then the problem must be in the mesh clearances between the two... if it doesn't then it's in the axial clearance for the crown wheel.

Sadly, it's not as simple as that... adjusting the axial clearance will affect the mesh clearances (as will adjusting the pinion axial clearances). All three need to be correct for the drive to function well.

Rob

[ME 109]

What does "fully rebuilding" comprise? What did you do? Did you fully dismantle the final drive, etc etc?