Failed rear diff bushings?

[loudspeaker69]

It sure seems like my diff has had enough. Anyone know a way to positively determine that the diff is the issue. The axles seem fine - no slop.

Jesse

If one wheel seems slipping/accelerating more even when DSC is on, that might be one way?

Turning DSC off and then encountering this may also confirm.

[D-O]

If one wheel seems slipping/accelerating more even when DSC is on, that might be one way?

Turning DSC off and then encountering this may also confirm.

I have verified the issue is present with the DSC either on or off. The problem will manifest without driving aggressively enough for the DSC to engage.

Jesse

[sapote]

The axles seem fine - no slop.

How exactly you check these CV joints?

As about bad diff, unless there are broken pieces of material that caught in the spider gears that can cause the clunk when they turned during a corner, I don't see what else in there can cause this. Worn clutch stack just acts like a normal open diff without LSD feature. You can hold and shake the diff output flanges up/down to see it they have excessive plays, especially the RHS unit.

[sapote]

Thanks.

This morning I got a fairly loud knocking in the driver's side rear when applying throttle in a corner. Not heavy throttle but not just a tiny bit either.
Jesse

Does the noise and vibration sound like clutch chattering? It could be the worn clutch stack (LSD) chatter instead of just smooth friction. Change the oil and use LSD additive or oil and see it it improved. If not, time to delete the clutch stack or install new set.

But if the clutch set chatter then regardless left or right turn it should cause the same chattering noise.

[D-O]

I have since found that I can feel the vibration more than I can hear it. The fluid has right at 15k on it (correct factory stuff), and I will be replacing it in the next few days, but I am not holding out much hope it will solve the problem. I work at a dealer (not BMW) and the consensus in our shop is that the LSD is beginning to fail. I called diffs online and described the problem, and they said its not uncommon and is a sure sign the LSD is failing. Of course, he would like to sell me a diff, so grain of salt.

I'd be happier if I could find a way to positively determine the diff is the issue. It is a bit troubling to me that it only manifests in one direction, but diffs online and some of the guys here are not surprised by this.

If anyone has any other ideas I would certainly like to hear them.

Jesse

[loudspeaker69]

I’ve heard somewhere that the test for a diff issue is to to a figure 8 in a parking lot (at parking lot speeds).

Full steering left and full steering right.
Good luck!

[sapote]

Jack up the left rear wheel off the ground, chock the other wheels. Run engine and drive in first gear. If left wheel spin with chattering then it is the diff clutch.

[old///MFanatic]

I have since found that I can feel the vibration more than I can hear it. The fluid has right at 15k on it, and I will be replacing it in the next few days, but I am not holding out much hope it will solve the problem. I work at a dealer and the consensus in our shop is that the LSD is beginning to fail. I called diffs online and described the problem, and they said its not uncommon and is a sure sign the LSD is failing.
It is a bit troubling to me that it only manifests in one direction, but diffs online and some of the guys here are not surprised by this.

Yep that’s why I listed it. Descriptions sounds a lot like the diff. It absolutely matches. And a bad LS diff doesn’t just act like an open diff, it makes noise. And saying it should do it both sides is also wrong. It certainly can do it one side only.

The fact it happened after sitting raised for months is something that interests me. Was the car raised level, or one side up other down? Since factory diff fluid is only 15k old I would just add some “friction modifier” to it and do the figure 8 break in instead of changing fluid. If diff was at angle when raised the figure eight fluid “break in” might also fix that.

[D-O]

Jack up the left rear wheel off the ground, chock the other wheels. Run engine and drive in first gear. If left wheel spin with chattering then it is the diff clutch.

This might be tricky to do safely.

Jesse

[D-O]

Yep that’s why I listed it. Descriptions sounds a lot like the diff. It absolutely matches. And a bad LS diff doesn’t just act like an open diff, it makes noise. And saying it should do it both sides is also wrong. It certainly can do it one side only.

The fact it happened after sitting raised for months is something that interests me. Was the car raised level, or one side up other down? Since factory diff fluid is only 15k old I would just add some “friction modifier” to it and do the figure 8 break in instead of changing fluid. If diff was at angle when raised the figure eight fluid “break in” might also fix that.

It was up on a set of quick jacks, so level all the way around (at least no less level than parked in my garage).

Jesse

[old///MFanatic]

It was up on a set of quick jacks, so level all the way around (at least no less level than parked in my garage).
Jesse

Going off “cause and effect” that doesn’t lean toward toward my additional theory the diff needs fluid pushed around inside it where it went dry.

[sapote]

This might be tricky to do safely.

Jesse

Just engage clutch pedal slowly at idle, and if the car wants to move then cut the clutch. At slow speed the left wheel will spin and the LSD will slip just like doing the RH turn, and I don't think the car will overcome the chocked wheels.

[heinzboehmer]

Just engage clutch pedal slowly at idle, and if the car wants to move then cut the clutch. At slow speed the left wheel will spin and the LSD will slip just like doing the RH turn, and I don't think the car will overcome the chocked wheels.

I think a much safer way to do this would be to lift the car up in the air, disconnect the left rear handbrake line in the interior and then pull the handbrake up. That way the handbrake will hold the right tire but not the left, with the added bonus that you don't get to test whether you can make the car fall off of jack stands or not.

[sapote]

I think a much safer way to do this would be to lift the car up in the air, disconnect the left rear handbrake line in the interior and then pull the handbrake up. That way the handbrake will hold the right tire but not the left, with the added bonus that you don't get to test whether you can make the car fall off of jack stands or not.

+++1

[D-O]

Long overdue update:

Bad shock along with a bad ECS monobal RSM. Pleasantly surprised.

Jesse