[SOLVED --> found the actual source of the noise] M3 diff bushings not visible on realoem?

mega_stihl · Sep 24, 2023

EDIT: update in post #6

So my friend's M3 came in for some maintenance stuff. There was also a complaint that there's a squeaking cracking sound from the rear. It sounded like dry PU bushings. So I lubed up the Powerflex RTAB's like I've done 3 years ago. Didn't solve the issue. Then when I took it for a drive I noticed the sound was present not when the springs compressed, but when there's a difference in load. By that I mean when accelerating/decelerating. So I had someone press the brake and let go of the clutch so there would be load on the drivetrain. And that's when I heard it more clearly from underneath the car.

I narrowed it down to the differential bushings. Couldn't feel it, but the moment these bushings were under load the sound came from directly there. The only issue I have is: these bushings DON'T show up on realoem. I'm not talking about #8, but I'm talking about those that bolt up with bolt #10. Can anyone chip in? And no, they are not visible on the differential pic. VIN is PM76074.

E46 M · Sep 24, 2023

The two rear diff bushings on e46 m3 are part of the diff cover, they are not available any other way. The front diff bushing is more likely to be the culprit and is available as a standalone part.

mega_stihl · Sep 24, 2023

so you're saying I am forced to replace the diff cover? Dang ... But then again, no surprise for an M3...
Maybe I'll double check just to be sure. Wasn't easy locating it with a relatively low lift and a second person in the car whose time I didn't want to waste for too long.

Alex323Ci · Sep 24, 2023

correct, the two rear diff bushings are part of the diff cover. BMW does not sell them separately to press in.

but some companies sell poly diff replacements. as you know I’m not a fan of those.
some have pressed in E36 M3 bushings. since the cover is cast aluminum, it’s tricky to press in and often gets cracked. so there’s that.

mega_stihl · Sep 25, 2023

I like poly, but I would never ever use poly for engine/tranny/diff mounts. Even for a dedicated track car. Thanks for the input guys.

mega_stihl · Sep 26, 2023

So the first time I had little time and quickly checked for the cracking noise. Today I took some time and rolled myself underneath the car and had someone apply the brake/clutch. The actual noise came from the FRONT differential bushing, and the bolt was very loose. Torqued it to spec --> problem solved.

Alex323Ci · Sep 26, 2023

that front diff bushing is the one i find wears out first. it is also not unheard of to have installed wrong and that bolt ruins the threads. so much so that even companies like Rogue Engineering sell a kit as a fix for those that have to deal with the aftermath.

Horto · Nov 12, 2023

The front bushing is normally the one to go first and causes alot of clunking noises. Poweflex, bushings are a good replacement option.
https://www.powerflexusa.com/shop/p...-bmw-e46-3-series-z4-rear-diff-front-mount-1274?category=1786&search=diff#attr=

[SOLVED --> found the actual source of the noise] M3 diff bushings not visible on realoem?

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