Diff making noise?

[flea333]

I took my M3 as there's a crunching sound from the back when I turn that is new. They suggest replacing the diff fluid. Does this make sense?

Concern
Critical
Customer States When He Makes Angled Turns At A Slow Speed Rear End Makes Crunching Noise

Cause
WHEN THE REAR WHEEL SPEED DIFFERENTIAL VARIES DURING TIGHT CORNERING, A SLIP/STICK EFFECT IS CREATED ON THE LINING AND STEEL DISCS INCORPORATED IN THE DIFFERENTIAL LOCKING CLUTCH CAUSES A GRINDING NOISE. THIS NOISE TYPICALLY GOES AWAY AS THE LOCKING CLUTCH DISCS IN THE DIFFERENTIAL WEAR IN. THE BREAK-IN TIME VARIES DEPENDING ON DRIVING HABITS; FOR EXAMPLE, TIGHTER CORNERING (WORKING THE LOCKING CLUTCH) MEANS THAT IT TAKES LESS TIME TO WEAR IN THE LOCKING CLUTCH DISCS.

Correction
PERFORM DIFFERENTIAL FLUID EXCHANGE

Estimate
$ 770.07

[EMKOOP]

The BMW SAF-XJ + FM Booster formula should be the most common/preferred way to cure this issue.

The $700+ quotation, however, is pure highway robbery.

[Helmsman]

Change the fluid yourself OP. Castrol Syntrax Limited Slip 75w-140. What BMW are selling but apparently a tad less FM. Easiest DIY there is assuming you have a lift around.
Ps. Made less grinding noise in my diff then the OE coming out, very rewarding.

[DukeofAlexandria]

Originally Posted by Helmsman

Change the fluid yourself OP. Castrol Syntrax Limited Slip 75w-140. What BMW are selling but apparently a tad less FM. Easiest DIY there is assuming you have a lift around.
Ps. Made less grinding noise in my diff then the OE coming out, very rewarding.

This is the way.

-Duke

[spammysammich]

fcpeuro sells a conveniently put together kit for servicing the diff that includes fresh drain and fill plugs as well. Easy as pie. Crack the fill plug first.

[flea333]

Thanks all for input. I gave dealer the OK to perform the diff fluid change. Only other thing I saw on this forum is where a member had a similar rubbing sound in the back and it was a bad carrier bearing.

I'll see if this clears it up.