Thud coming on/off throttle - diff bushings?

[TassieBMW]

My E90 with around 100,000 miles has a decent thud in the driveline at the rear end coming on and off the throttle as whatever is loose takes up slack.
Under some conditions like coming off a light throttle application it also causes a weird jerking back and forth sensation.

I already previously successfully addressed the cowbell noise with a new guibo and CSB, however the CV joint is still original.

To me, it seems like this should be a differential bushing failure, but looking at them from beneath the car they don't look to be obviously beat up or cracked.

What other things could be a likely cause of this?
Internal diff gear wear, engine mounts, subframe mounts, etc?

TIA

[DrFerry]

Originally Posted by TassieBMW

My E90 with around 100,000 miles has a decent thud in the driveline at the rear end coming on and off the throttle as whatever is loose takes up slack.
Under some conditions like coming off a light throttle application it also causes a weird jerking back and forth sensation.

I already previously successfully addressed the cowbell noise with a new guibo and CSB, however the CV joint is still original.

To me, it seems like this should be a differential bushing failure, but looking at them from beneath the car they don't look to be obviously beat up or cracked.

What other things could be a likely cause of this?
Internal diff gear wear, engine mounts, subframe mounts, etc?

TIA

Failed driveshaft coupling center bearing.

[TassieBMW]

Originally Posted by DrFerry

Failed driveshaft coupling center bearing.

Coming back to this after a while as I'm keen to get this sorted.

I replaced the centre bearing and the guibo, it fixed the cowbell noise but there is still a thud during load reversals, where something at the rear end has play in it.

Diff bushings seem like the obvious culprit, the only other things I can think of would be driveshaft CV joint or subframe bushings, although I highly doubt the latter.

I guess a worn diff with play in the gears is also a possibility but surely not.

[serranot]

Originally Posted by TassieBMW

Coming back to this after a while as I'm keen to get this sorted.

I replaced the centre bearing and the guibo, it fixed the cowbell noise but there is still a thud during load reversals, where something at the rear end has play in it.

Diff bushings seem like the obvious culprit, the only other things I can think of would be driveshaft CV joint or subframe bushings, although I highly doubt the latter.

I guess a worn diff with play in the gears is also a possibility but surely not.

I wouldn't rule out anything in the driveline that is subject to Newton's laws. Bad mounts, bushings etc can result in a lot of unwanted motion. All of your motor mounts etc in good shape?

[RocketyMan]

Originally Posted by serranot

I wouldn't rule out anything in the driveline that is subject to Newton's laws. Bad mounts, bushings etc can result in a lot of unwanted motion. All of your motor mounts etc in good shape?

Yeah good point.

OP, is everything "tight" under there? Bolts/fasteners on the subframe, diff housing, CV axles to carrier, etc...

[SalimM3]

I had these same symptoms. On/off throttle movement in the driveline at 150k miles. I replaced the engine and trans mounts. Nothing changed. The car already had the center support and guibo changed at like 137k. I went on to replace the rear subframe bushings and diff bushings. The on/off throttle movement has improved but its not totally gone. The only thing left at this point is the driveshaft or the CV joint in the driveshaft. Its pretty annoying after changing all that its not gone, but next up is going to be a 1 piece aluminum driveshft from SLG.

[nycplumber]

Another vote for driveshaft and replacing it with SLG unit.

[Edwardsc1]

I have this exact same issue. Started happening over the last 3-4 months - my driveline was completely solid before, no play at all. I had the car checked out last month and my shop said everything was tight and all bushings looked good. CSB, guibo, etc all looked good as well.

I'd be interested to see if you figure out what it is, because I haven't been able to. I definitely don't like driving it around just waiting for something to break.

[DrFerry]

Originally Posted by TassieBMW

Coming back to this after a while as I'm keen to get this sorted. I replaced the centre bearing and the guibo, it fixed the cowbell noise but there is still a thud during load reversals, where something at the rear end has play in it. Diff bushings seem like the obvious culprit, the only other things I can think of would be driveshaft CV joint or subframe bushings, although I highly doubt the latter. I guess a worn diff with play in the gears is also a possibility but surely not.

You're on the right track. Considering all you have replaced the next most likely culprit is the ring and pinion Diff gear backlash. If your Diff whines at 2500RPM when in top gear, then the Diff has some backlash gear tooth wear, The Difff bushings are a known failure point item, they're cheap and easy to replace. However, the OEM Diff LSD is made by ViscoLok and the viscous fluid and discs can cause clunks as well as poor performance at corner exit. The Diff carrier also has a nose bearing but it makes an awful whine when it goes rather than a clunk:

Recommendations:
1) Replace all Diff bushings
2) Check for worn universal joints on the Diff end of the driveshaft
3) Get under the car and try to rotate the driveshaft when in neutral by hand to locate the clunk and determine if the ring and pinion backlash is excessive i.e. the clunk culprit
4) Consider replacing the LSD and getting the ring and pinion backlash adjusted when you're in there.

PS: I very much doubt it's the CV axles because they don't move when your foot is on the brake and that's when the clunk happens i.e. before the car moves.

[RocketyMan]

Originally Posted by DrFerry

You're on the right track. Considering all you have replaced the next most likely culprit is the ring and pinion Diff gear backlash. If your Diff whines at 2500RPM when in top gear, then the Diff has some backlash gear tooth wear, The Difff bushings are a known failure point item, they're cheap and easy to replace. However, the OEM Diff LSD is made by ViscoLok and the viscous fluid and discs can cause clunks as well as poor performance at corner exit. The Diff carrier also has a nose bearing but it makes an awful whine when it goes rather than a clunk:

Recommendations:
1) Replace all Diff bushings
2) Check for worn universal joints on the Diff end of the driveshaft
3) Get under the car and try to rotate the driveshaft when in neutral by hand to locate the clunk and determine if the ring and pinion backlash is excessive i.e. the clink culprit
4) Consider replacing the LSD and getting the ring and pinion backlash adjusted when you're in there.

PS: I very much doubt it's the CV axles because they don't move when your foot is on the brake and that's when the clunk happens i.e. before the car moves.

There's only one u-joint at the CSB. The diff end is a rzeppa joint. These don't normally go bad unless they lose all their grease it seems. Worst case is the rzeppa get's a little "notchy" from brinelling that i've noticed. But closer investigation it def needed.

It'd be nice to find a replacement rzeppa as I'm needing one.
https://www.driveshaftparts.com/CVJ069

I do agree that the OP needs to get the rear end up in the air and do more investigative work. And also if the front pinion seal has leaked enough, the front diff bearing is the first to go.

[SalimM3]

The do sell a replacement for the CV joint

https://www.fcpeuro.com/products/bmw...m6-26112282725

[RocketyMan]

Originally Posted by SalimM3

The do sell a replacement for the CV joint

https://www.fcpeuro.com/products/bmw...m6-26112282725

Yeah. I saw that. $350 for a replacement joint plus shipping...oof.

[DrFerry]

ViscoLok LSD and Rzeppa joint information:
.
https://www.kmpdrivetrain.com/drives...-rzeppa-joint/
.
https://www.scribd.com/document/513686174/ViscoLok-engl

[RocketyMan]

Originally Posted by DrFerry

ViscoLok LSD and Rzeppa joint information:
.
https://www.kmpdrivetrain.com/drives...-rzeppa-joint/
.
https://www.scribd.com/document/513686174/ViscoLok-engl

That's pretty neat!

So looking at that, it makes sense why the output flanges-splines plugging into the carrier are different lengths between left and right.

It is possible, but the splines could also wear out causing a "thud" between drive and coast. I just don't think it's common on our cars or the OP's issue.

OP, did you ever do a drain and refill on the diff? Any question about the diff condition might be telling if liquid-disco-party drains out or not.

[TassieBMW]

Thanks for the replies.

I think I'm going to go ahead and do diff bushes and possibly also trans mounts (engine mounts were done recently) to see if that helps.

I fear that it may be diff backlash due to wear though. Having said that, I'm not getting much (or any) whine that I'm aware of, so perhaps it's actually ok.

My other thought is could this be some sort of wear internally inside the DCT? How do worn flywheels and DCT clutches exhibit their symptoms?

I don't want to throw a heap of money at different parts chasing the issue as I'm unsure how long I'll keep the car, but would like this sorted either way as it can make driving it rather unpleasant and frustrating.

[Thumbie]

Great opportunity to get some powerflex diff bushings!

Originally Posted by DrFerry

Recommendations:
1) Replace all Diff bushings
2) Check for worn universal joints on the Diff end of the driveshaft
3) Get under the car and try to rotate the driveshaft when in neutral by hand to locate the clunk and determine if the ring and pinion backlash is excessive i.e. the clink culprit
4) Consider replacing the LSD and getting the ring and pinion backlash adjusted when you're in there.

PS: I very much doubt it's the CV axles because they don't move when your foot is on the brake and that's when the clunk happens i.e. before the car moves.

I'd start with #3 because it is the most free