Rear Diff mount clunk noise

[nextelbuddy]

in my S54 wagon, I originally installed E36 M3 diff cover bushings in my rear diff cover and reused the stock bolts. i had a loud clunk when going into reverse or changing from reverse to 1st gear. i was able to find and replicate it on the 4 post lift with a pry bar and could rock the diff and hear the noise.. i then got the updated Diff mount bolts that had the large diameter shank before the threaded portion and that solved it immediately. installed, torqued and stretched per spec

now the sound has come back. same exact sound but more faint and doesn't happen every single time like before. am getting annoyed at this, and wondering if the e36 bushings are not the way to go and instead should update them to AKG diff bushings (yes i know there will be SOME wine as i have them in my red turbo car)

or just replace the cover with a brand new genuine BMW cover with new e46 diff mounts.

just baffles me that the sound has come back with new mounts and bolts. wondering if other people with e36 mounts in their diff covers ever experienced something similar.

[maupineda]

My Z4M has it, and has the newer bolts from the factory. So maybe your diff?

[PetrolM3]

It’s possible the softer E36 rubber bushings have deteriorated, even further with the new bolts, and have more give than before. I would recommend a brand new E46 M diff cover with OE bushings.

Having a similar issue with my non-M at the moment. I got the clunk and saw some small cracks in the big diff bushing so I replaced it. It seemed better but than the clunk came back with a vengeance. Pretty sure the two smaller bushings are toast since the new big bush made them the weakest link and take additional abuse so I will replace those next. Should have just done all 3 at once. Hope that takes care of it…

[PetrolM3]

Update - I just replaced the two smaller bushings on my non-M and it fixed the clunk. They were worn out and soft enough to allow the diff to move and make contact with the subframe. Replacing only the big bush (which is usually the culprit) had made this issue worse.

While I realize the non-M diff is mounted on the subframe differently than M (big bushing is in the rear and two small ones in front), I suspect you have the exact same issue I had with your E36 rubber pieces which are not stiff enough for E46 M and allow too much movement. I’m sure that replacing the cover with genuine BMW will resolve your issue.

Good luck and let us know how it goes!