Rear Diff Issue

[Cubieman]

It's up in the air, the front bushing looks fine, the rears not so much possibly. When I try and move the diff by hand it is rock solid.
The driveshaft has about 1/10th or so rotational play, the passenger side halfshaft has a small about of up/down play whereas the driver's side is rock solid.
The guibo has a few cracks developing in it, also if I rotate the rear wheels backwards then rotate them foward quickly it feels like there is some play there as well as a clunking sound when I do that.

https://youtu.be/tmIfkucctuc

https://youtu.be/0vl-VaJ4OiA

https://youtu.be/pH3W2TB-UaU

Edit: that video of the rear diff. bushings is worthless after uploading it.

[eacmen]

I will just do the OE bushes then, I liked the poly because it looked like the install may be easier. I'll be putting it in the air today to check the rear bolts and everything else.

If the front bushing was gone it would be readily aparant when you have in in the air. The front of the diff would move if you shake it. What normally happens is the front diff bolt backs out thus ruining the bushing.

If you want to go OE rear bushings you need to get the whole diff cover. Cant buy OE replacement bushings. Some claim the E36(?) ones can be pressed in but not sure what the conclusion on that was.

[Cubieman]

Yeah you can replace the front diff bushing without dropping the subframe but it's a bit of a pain since there's not too much space. Also know that poly bushings add significant NVH. I've got some on my car and the diff whine is pretty loud. I'll probably go back to OE soon.

I will just do the OE bushes then, I liked the poly because it looked like the install may be easier. I'll be putting it in the air today to check the rear bolts and everything else.

[Obioban]

OP: make sure the rear mount bolts haven’t loosened.

[heinzboehmer]

Can all 3 diff. bushings be replaced in situ? The rears I can see, but not the front unless the subframe and/or diff. is dropped. Looking to do the power flex bushes. I have 4.10 gears and get a pretty good clunk here and there. The diff. was rebuilt with 4.10s in 2015 by an indy shop by the previous owner, wish I had more information on it.

Yeah you can replace the front diff bushing without dropping the subframe but it's a bit of a pain since there's not too much space. Also know that poly bushings add significant NVH. I've got some on my car and the diff whine is pretty loud. I'll probably go back to OE soon.

[Cubieman]

Can all 3 diff. bushings be replaced in situ? The rears I can see, but not the front unless the subframe and/or diff. is dropped. Looking to do the power flex bushes. I have 4.10 gears and get a pretty good clunk here and there. The diff. was rebuilt with 4.10s in 2015 by an indy shop by the previous owner, wish I had more information on it.

[Mainman857]

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

[bigjae46]

In an extreme case the side flanges could come loose.

[Mainman857]

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

[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]

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.

[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]

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

Harbor frieght problems haha

[///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.

[Ianb]

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