On/Off Throttle Clunk Diagnosis

[R1pilot]

Rear diff cover bushings.

[PSUEng]

Curious. How did you diagnose?


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Truthfully, months ago I got under the car to check things out during my oil change. I noticed the rear bushings just "looked" off, but didn't think much of it. Fast forward to yesterday, I took the car to an indy shop I've worked with for years and while on the lift, you can wiggle the diff. I've had this car for 15 years, since 27,000 miles and when driven, it's mostly highway, and never abused. I've got a video, but unable to post it here.

[sapote]

The theory is as the clutches and steels wear it creates clearance which results in lash in the spider gears. This lash is the source of a clunk.

I might have mentioned this in other threads, but the clutch pack total thickness doesn't affect the spider gears lash. Between the spiders and the clutch pack is a thick steel plate which rested against the LSD carrier housing shoulder, not on the spiders. The other way to see this is that if the clutch pack pushes on the spiders, then there is absolutely zero gear lash at both output flanges, but this is not the case.

The worn clutch doesn't cause more backlash on the spiders, but it does cause the M-clunk.

[eacmen]

Turns out, rear diff bushings are totally shot. At 81.5k, no track time, arguably driving like a grandpa--totally shot. I guess these just rot away....So, off to the shop as I'm not setup to do this at the house--unfortunately.

Curious. How did you diagnose?


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[PSUEng]

Turns out, rear diff bushings are totally shot. At 81.5k, no track time, arguably driving like a grandpa--totally shot. I guess these just rot away....So, off to the shop as I'm not setup to do this at the house--unfortunately.

[bigjae46]

Here is what the insides of a V1 diff looks like...





The theory is as the clutches and steels wear it creates clearance which results in lash in the spider gears. This lash is the source of a clunk.

The V2 unit isn't very different except the top screws on. You do have some adjustability to add static preload with the V2. As I've found out, you can add too much and cause a groaning noise.

[eacmen]

What numbers should one look for?

https://nam3forum.com/forums/forum/main-forum/e46-2001-2006/168913-do-i-need-a-diff-rebuild/page2

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[Cubieman]

To test clutch packs jack up one rear wheel, leave the other side on the ground chocked on both sides. Put the car in neutral e brake off. Put a torque wrench on the axle nut and measure the breakaway torque.


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What numbers should one look for?

[PSUEng]

There is always plays from from the long drive shaft to the wheels, so it is normal to have the plays that you saw. I don't think rotating the wheels can tell if clutch pack slip -- at least not the way you did.
To do: jack up the rear wheels, shift to 1st gear, engine off, try to rotate the left wheel and if the clutch slipping really bad then the right wheel should rotate backward. If you couldn't make the right wheel to rotate backward then this doesn't mean the clutch pack is good though, as a worn clutch still can slip during take off and causes the clunk (I posted a detail explanation on this).

Thanks! I'll give this a try...

[sapote]

I got both rear wheels up in the air and in neutral/e-brake off, there is noticeable play when rotating each wheel. More of a thud on the driver side and clicking on passenger side--but play on both sides. Mine is a 12/02 build, 81.3k miles. So then, clutch packs wearing? How long can I drive like this and what else will wear out until I fix it?

There is always plays from from the long drive shaft to the wheels, so it is normal to have the plays that you saw. I don't think rotating the wheels can tell if clutch pack slip -- at least not the way you did.
To do: jack up the rear wheels, shift to 1st gear, engine off, try to rotate the left wheel and if the clutch slipping really bad then the right wheel should rotate backward. If you couldn't make the right wheel to rotate backward then this doesn't mean the clutch pack is good though, as a worn clutch still can slip during take off and causes the clunk (I posted a detail explanation on this).

[Ramps]

Preload CSB or not doesn't cause the clunk. It affects the bearing noise or its life span.

Mine clunks when i clutch in coming up to a stop, not quite the typical M-clunk, it feels like when the clutch plate is pressed there’s drivetrain movement. I never heard this noise before I did all the bushings…it could just be the solid SF bushings transmitting more noise through the chassis I guess.

[eacmen]

I got both rear wheels up in the air and in neutral/e-brake off, there is noticeable play when rotating each wheel. More of a thud on the driver side and clicking on passenger side--but play on both sides. Mine is a 12/02 build, 81.3k miles. So then, clutch packs wearing? How long can I drive like this and what else will wear out until I fix it?

To test clutch packs jack up one rear wheel, leave the other side on the ground chocked on both sides. Put the car in neutral e brake off. Put a torque wrench on the axle nut and measure the breakaway torque.


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[PSUEng]

I got both rear wheels up in the air and in neutral/e-brake off, there is noticeable play when rotating each wheel. More of a thud on the driver side and clicking on passenger side--but play on both sides. Mine is a 12/02 build, 81.3k miles. So then, clutch packs wearing? How long can I drive like this and what else will wear out until I fix it?

[Tones]

My car has the same. Jack up your rear and move the wheel back and forth by hand. When i did this the clunk was from the diff and it's loud. The clutch packs in the lsd wear out around 80-100k. Mine started around 120k after lots of mtn runs

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[sapote]

What do you guys think? If it's the driveshaft, I like a complete rebuilt solution like the Beyer.

More likely I think the old LSD clutch pack slips then the side-gear hammers the spiders. To fix: new clutch pack and reduce the plays at the side-gears.