Rear Diff Issue

[Mainman857]

Hey new to the M3/BMW world.

I have a 2006 comp pack with 129k.
the rear diff makes a decent clunk when shifting at rpms above 3k.
I know the M3 has a M3 diff clunk but never being in these cars before this sounds excessive.
You can hear the load come off the diff and then back onto the diff.
replaced the cv axel, diff mounts, and fluid.

Still makes the noise.

Feels like slop inside of the diff when driving the car.

Am I on the right train of thought thinking here?

[Cubieman]

Diff bushings, check the 2 on the rear diff. cover. I don't think BMW sells these so must replace the whole diff. cover with new factory bushings, its about $190 or so. Or just buy some poly bushings.
Make sure to check your front diff. bushing, this one may have more to do with clunk than the rears.
Also the diff. bolts themselves can be comprised.
If you can jack the rear up and and SAFELY have someone drive slowy/shift you may be able to locate the problem area.
Alternatively you could set up a video camera to watch the diff. then engage your parking brake a bit as to simulate a load, then drive with the rear jacked up.

[Mainman857]

When I said diff mounts I ment diff bushings.
I had a shop do the work cus they where in there anyway.
can I see if they actually replaced these parts as they said they did without taking everything off the underside of the car.

Bought the ecs 3 pack kit.

[Cubieman]

I don't think they could have replaced the 2 rear bushings without pulling off the rear cover. So you would have likely had a charge for diff. fluid/gasket on your bill.
Also I don't know how in the hell you would replace the front diff. bushing in situ but I've never done it.

I plan to replace all 3 this summer and as far I know I'll have to remove the diff. entirely.

[Mainman857]

Just checked they deffently did back 2 and I have 3 pressed out bushings in the old part box. Sounds like might have some diff slop.

That's what I'm thinking anyway

[beefaroni]

Center support bearing, driveshaft, or flex joint?

[Ianb]

Can be slack in the diffs internal spider gears, mine has this, a special shim is available from Racing Diffs to cure it.

[///Mac]

I just rebuilt the diff in my 2002 M3 with 150K on the clock. I initially had the common diff clunk everyone talks about and a few months after buying the car I also began to hear whining / grinding coming from the diff. After the grinding started I parked the car until I figured out what to do, eventually deciding on a full rebuild with upgrade to 4.10 gear set.

My diff had significantly more backlash than spec (slop) which played a big role in the clunk I was hearing. The passenger side output flange had significant play which also contributes to the clunk. Upon disassembly I found the outer pinion bearing failed and the bearing race was also worn out which is what caused the grinding, so the full rebuild was the right call.

The slop is gone after rebuild now that backlash and bearing preloads are correct. I installed the "clunk fix shim" from Racing Diffs to eliminate the slop in the passenger output shaft which is caused by improper preload on the spider gears. It was a huge amount of work and learning but worth every penny - especially since i went with the 4.10 gears.

Based on OP's symptoms, that diff may be due for a rebuild or at minimum an inspection to check bearings, backlash, etc, and if you're that far in you'll at minimum want to replace seals, o-rings and even carrier bearings if there's any chance they're bad.

To check backlash in a non-scientific way, jack the car up and in neutral with minimal engagement of the parking brake to simulate load and rotate the input flange/driveshaft a few degrees in each direction and see if it produces a clunk every time you change direction. With backlash in spec you'll hear minimal noise as the pinion and ring gears make contact, but I wouldn't call it a clunk. If there's slop, you'll have more play and more noise. The max backlash on these diffs in something like 0.005" so there should be very little play if it's still within spec.

[Mainman857]

Sounds good il give that a try once my new jack stands come in.

Harbor frieght problems haha

[poth2034]

its most likely the small diff bushing that gets pressed into the subframe. most shops find out its a pain to replace and just say they replaced it.

[Mainman857]

Got the car up on jack stands today and simulated the noise.
I found that the diff makes a loud clunking noise along with the driver side axel has play where it makes contact with the diff, passenger side is tight.
my guess on drive shaft slop is around 1/16 of a turn at most, with contact after the play has been taken up.
diff makes no grinds or other noises.
is this something shims could fix or is it time for a 4.1 diff update/upgrade.

[bigjae46]

There is probably play in the spider gears inside of the diff. I’d bet that wear on the clutch plates allows more play in the spider gears. I’d be curious to see the condition of the clutch plates and steels.

[Mainman857]

Is there any more damage having this much play can cause to other parts of the driveline?

[bigjae46]

In an extreme case the side flanges could come loose.

[Mainman857]

Where the driver side axel meets the diff has slight up and down play is this normal? Passenger side is tight no slop.