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      03-27-2016, 08:21 PM   #1
Jim621
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LSD diff backlash issue - N55 DCT car

Hi All,

A while ago I bought a secondhand diff which had a quaife LSD fitted.

Recently i fitted it to my car, and have found out it has quite a large amount of slop between the driveshaft and the axels (not sure if its crownwheel and pinion slop, or within the LSD gears) and it has some diff whine at highway speeds (greater than 80kph).


Where could the slop be coming from?


is there a crush sleeve on the pinion shaft that could have deformed under high load?
i know the diff centre is held in position by specific thickness shims, so i wouldn't expect that to move. and the diff wouldn't be old enough to get wear on the diff gears to create slop.
since the diff has a bit of noise at highway speeds, my gut feel is the backlash is out between the crownwheel and pinion.

Can anyone suggest how this slop and noise could happen?

Cheers, Steve.
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      03-28-2016, 08:49 AM   #2
Jim621
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Anyone have a photo of a stripped down BMW DCT diff?
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      03-29-2016, 05:56 AM   #3
Jim621
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Anyone?
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      03-29-2016, 06:31 PM   #4
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My Quaife whines. If you bought a whole diff setup, it sounds to me like that diff was just never shimmed properly to minimize whine. When I bought mine they said they "don't make shims" for this diff. It requires skill for sure. Mine has not gotten worse after the first year few months and I have around 70k miles on mine now.
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      03-30-2016, 05:44 PM   #5
Jim621
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Thanks Eyeman.

Sorry i probably didnt explain myself properly - my main concent with the diff is the slop, rather than the whine. yes the whine is annoying, but the freeplay/slop is concerning.
The DCT trans produces some violent gear changes sometimes, likely due to the freeplay/slop in the diff...also, going from forward gears to reverse, you get a clunk running through the drivetrain when it takes up the slop.

I find the comment "they dont make shims" from your workshop hard to believe.

cheers,Steve
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      03-30-2016, 05:47 PM   #6
Jim621
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Ive found this website that sells the crush sleeve for supposedly 'all BMW' diffs from 1970s to current.

So im hopeful the crush sleeve in my diff has deformed, causing the excess slop.

https://www.difflab.com.au/BMW-Diff-...eve-lock-plate


Next question, does anyone know the torque required when installing the pinion nut to crush the crush sleeve?

thanks, Steve
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      03-30-2016, 06:07 PM   #7
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Quote:
Originally Posted by Jim621 View Post
Ive found this website that sells the crush sleeve for supposedly 'all BMW' diffs from 1970s to current.

So im hopeful the crush sleeve in my diff has deformed, causing the excess slop.

https://www.difflab.com.au/BMW-Diff-...eve-lock-plate


Next question, does anyone know the torque required when installing the pinion nut to crush the crush sleeve?

thanks, Steve
You need to measure the amount of backlash with the appropriate Dial indicator and ensure it's within spec, I'm going to assume it's not at this point.

The crush sleeve doesn't do anything for back lash, since it's only job is to maintain bearing preload on the pinion bearings.

If the back lash is out of spec, the only solution is to confirm the pinion depth is within spec, and adjust with the appropriate shim, and THEN shim the diff to acheive the correct back lash.

They make shims for the differential. It's not a brand specific thing, and you'll have to take your diff to a driveline shop to have it set up the correct way.

Good luck and let us know how it goes.
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      03-30-2016, 06:07 PM   #8
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From everything I have read/heard, you don't want to mess with the crush sleeve unless you have to because of a pinion bearing replacement. I'm pretty sure Mfactory sells shims. Let me try to find the link.

Here you go...

http://technik.teammfactory.com/diff...-rebuild-parts
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      03-30-2016, 06:22 PM   #9
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On more thing... Before doing anything to the diff, check to make sure the drive shaft nut has not backed off. I was getting a serious clunk when engaging gears. When I got under the car, I found the nut had come loose. I'm pretty sure my mechanic forgot to use loctite. Once I tightened the nut w/red loctite, 90% of the clunking went away. That being said, it seems that some helical diffs will always have a bit of play which is unrelated to the ring and pinion backlash.
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      03-31-2016, 04:55 AM   #10
Jim621
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Thanks for the response guys.

Uber///Madd - my understanding is the crush sleeve will significantly affect the backlash, since if the crushsleeve is 'overcrushed' the tapered pinion bearings will be extremely loose and allow sideways and 'in/out' movement of the pinion(due to the tapered shape of the bearing), which will be seen as excessive backlash.

Pig Farmer - yeah ive checked and retightened the driveshaft nut - no problem there.
The shim kit you refer to is for a solid pinion sleeve, which replaces the crush sleeve. The previous owner of the diff was running more power than stock, so im thinking the crush sleeve hasnt held up to the abuse.

Thanks.
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      03-31-2016, 10:10 AM   #11
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We have both the shim kit for the LSD/Ring Gear, as well as our solid pinion sleeve (which replaces the weak oem crush sleeve)
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      03-23-2020, 06:13 AM   #12
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This is an old thread..
Tobiasz17azs, there is a separate F8x forum where you may find more assistance. Check the diff mounts to begin with. Noise from the DCT is subjective so you may need to do a back to back comparison with another car of similar spec and mileage/age.

Back to the OP: DCT diffs have almost zero backlash. I replaced a pinion seal in mine and it's absolutely vital to mark the pinion and pinion nut position and depth prior to undoing it (punch it and also measure the protrusion). You do up the nut to the same position and depth as those markings/measurements. If you don't then you will change the preload.

Shims can be purchased through Mfactory
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