FAQ Medium Case Diff Rebuild

[BenTomm17]

q20v
Congratulations on your diff rebuild. I haven't seen anyone else ask but would you consider doing another rebuild? Specifically a 3.25 LSD from my '86 535. Diffs locally have been hard to find (other than a 500k mile unit with few if any oil changes). And haven't seen any on the various sites with 3.25 ratio and LSD, though would consider a 3.46 LSD.
My diff exhibits the same speed related noise, though sounds like a loud lathe rather than a Metallica concert. That's loud! Great write-up.
Ben

[q20v]

Sorry for the late replies guys. Had a busy summer and only drove the BMW a small handful of times, so it fell down the priority list and hence a lower interest in browsing BMW-related forums.

@ q20v
It just blows my mind the amazing talent and dare of so many people here in this forum like yourself.
Barry, you just arrived and earned first place on my personal E28 hero podium (not that it matters) but appreciate your well documented post.
Love your helper too. My 9 year old daughter will feel encouraged as well. Good luck!

I may have a question soon.
-Jack

Thanks Jack! Glad you enjoyed the read and hope you took something away from it. I'd love to have more time to post more content but usually end up just getting the job done and moving on. The diff rebuild was a winter project so I had lots of time! I think the next one will likely be a paint correction. Not sure if people are interested in the details of polishing paint but at least I'll post some highlights in my project thread.

q20v
Congratulations on your diff rebuild. I haven't seen anyone else ask but would you consider doing another rebuild? Specifically a 3.25 LSD from my '86 535. Diffs locally have been hard to find (other than a 500k mile unit with few if any oil changes). And haven't seen any on the various sites with 3.25 ratio and LSD, though would consider a 3.46 LSD.
My diff exhibits the same speed related noise, though sounds like a loud lathe rather than a Metallica concert. That's loud! Great write-up.
Ben

Hey Ben, thanks! I'd certainly entertain the idea.. shipping to / from New Jersey might be expensive though. I do have an address on the US side (13669) that can receive / ship packages. I realize I'm a bit late seeing your message so let me know if you're still interested.

Barry

[Zeuropa]

Huge thanks to q20v for this really detailed write-up. The result is a diff that looks brand new. Well done sir!

Question for the group: Is it possible to replace the output flange seals *without* removing the side plates from the diff housing?

TIA

[alemac1]

superb write up, has made me aware of a few things i didn't know i needed to know

[jhh925]

Fantastic write-up and super-helpful pictures. I've used this post now a bunch of times.

For reference on the running drag measurements for the bearing pre-loads, this is from a Metric Mechanic PDF:

Pinion bearings are separated by a “boa neck” crush collar that must be collapsed first in order to preload the [pinion] bearings for 14 to 16 inch pounds of rolling torque. Preload specs for the carrier bearings are 9 -11 inch pounds of rolling torque. This is accomplished with shims that are installed between the differential case and the carrier bearing housing. They also “shim-up” the backlash on the ring and pinion.

Here's a link to the MM document. Preloads are discussed on page 8.

[thrty8street]

Thank you for this invaluable resource! I did have two questions - what is the purpose of the thread sealant, to stop leaks? And, is the thread sealant a requirement?