Look inside of a diff that had the M Clunk

[bigjae46]

I rebuilt a diff for someone that had a clunking and grinding diff. It was obvious, you can move the output flanges by hand and hear the clunk. You can see the play in the spider gears with the back cover off.

Here are the clutch discs. They are super smooth and shiny with zero grip to them. They look worn out. I have no idea what the thickness is when new.



The spider gears had play. Likely due to the wear in the clutch plates causing more clearance. More clearance in the clutch packs creates more backlash in the spider gears which will cause a clunk noise when taking off from a stop.

You can see wear on the large spider gear



Wear on the small spider gears

[lvm3sm46]

How many miles on it?

[Cubieman]

Likely what's going on with mine, I have the diff. out and the passenger side OPF not only has what I feel is too much (I know there should be some) rotational play but also some up/down play.

Where do you source the spider gears once worn down? I would love to take this opportunity to rebuild the diff. but unsure of my ability to put it together correctly.

The PO of the vehicle had the diff rebuilt with 4.10's in 2014, I'd love to switch to a 3.91 or stock gearing.

[cobra]

Mine also has noticeable backlash. Is it something we can diy fix?

[maupineda]

Likely what's going on with mine, I have the diff. out and the passenger side OPF not only has what I feel is too much (I know there should be some) rotational play but also some up/down play.

Where do you source the spider gears once worn down? I would love to take this opportunity to rebuild the diff. but unsure of my ability to put it together correctly.

The PO of the vehicle had the diff rebuilt with 4.10's in 2014, I'd love to switch to a 3.91 or stock gearing.

interesting how some have what others desire so much LOL. 4.1 in my opinion is how the car should have been. you will for sure feel the car very lack luster after having 4.1

[DoubleSidedTape]

interesting how some have what others desire so much LOL. 4.1 in my opinion is how the car should have been. you will for sure feel the car very lack luster after having 4.1

I’d agree if that also included a longer 6th to compensate. With stock gearing I’m very happy with 3.85 and going to a car with a stock diff even that difference was very noticeable.

[oceansize]

I thought M-Clunk was present from day one with these cars and not something that developed. Weren't people discussing this way way back in the day or am I wrong? Or perhaps we just notice more because it gets worse with mileage?

[bigjae46]

Mine also has noticeable backlash. Is it something we can diy fix?

Racing Diffs sells a shim which is a Belleville spring which removes the excessive backlash. The shim adds preload which will add wear to the clutches but also lock up faster.

You can’t get the spider gears separately. I might try and send those out to get REM polished to see if that cleans up the surfaces. They are perfectly usable as is.


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[mrgizmo04]

Jae, what clutch pack did you rebuild with? Did you use the racingdiffs kit with the preload shims?

This is the only thing I see in the v2 lsd unit design that is potentially "better" - since spider gears have a through pin that secures them to the lsd case and they are held at "constant" backlash to each other, irrespective of clutches wearing down and don't create space and a different lash pattern, like v1 design does.

Spider gears can be purchased from racingdiffs, they do have a 210mm variant, for both large and small spider gears.

https://racingdiffs.com/collections/differential-tuning-parts/products/bmw-lsd-large-spider-gear?variant=33547067850887

https://racingdiffs.com/collections/differential-tuning-parts/products/bmw-lsd-small-spider-gear?variant=33547061264519

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[Cubieman]

Could anyone help me out with the part number for the bolts (not the etorx) that attach the OPF to the diff?

I assume these should be replaced as they are torqued then angled.

[fattycharged]

Racing Diffs sells a shim which is a Belleville spring which removes the excessive backlash. The shim adds preload which will add wear to the clutches but also lock up faster.

You can’t get the spider gears separately. I might try and send those out to get REM polished to see if that cleans up the surfaces. They are perfectly usable as is.


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Any chance you want to rebuild another one while you're "in the zone"

[jet_dogg]

So glad I don't have to deal with this anymore.

[bigjae46]

Any chance you want to rebuild another one while you're "in the zone"

Diff or LSD carrier only?

Actually, I enjoy rebuilding these.


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[0-60motorsports]

Racing Diffs sells a shim which is a Belleville spring which removes the excessive backlash. The shim adds preload which will add wear to the clutches but also lock up faster.

You can’t get the spider gears separately. I might try and send those out to get REM polished to see if that cleans up the surfaces. They are perfectly usable as is.


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The dont sell it separately any more as i wanted to buy it and they said i would have to buy it in a package with other parts.

[Cubieman]

Does anybody know the part # axle cap bolts? I don't know that I should re-use these..