M5 Differential

[Syndrome]

Hey all. I’m chasing down a sort of scraping sound on the rear left of my car, a USA E28 M5. I thought it might be a wheel bearing, but it only happens when I’m in gear and accelerating. Neutral, no noise. I replaces my brakes and half shafts. While I was there, I replaced my dog bones and sway bar links. Why not. Sound still there. I’m wondering if it might be my differential making the sound, but I don’t know it is for sure.

First, is this something anyone else has encountered on these old M5s? If so, what did it end up being? Second, assuming it’s my differential, is this something a home mechanic can do in the garage? What’s involved? BTW, how do you determine a differential is the source of unusual sounds?

Finally, is there a reliable source for rebuilt differentials for these cars? Was the same differential used on other model BMWs? I’m thinking 733i, or similar.

Thanks for the advice.

[Fanclutchnut]

Did you check the e brake system?

[Syndrome]

I replaced all four rotors, so I pulled it all apart. The thing is, it makes the noise when I throttle up but not coasting. To me, this means that it makes noise when something in the driveline is spinning. I wonder, for example, could it be something really stupid, like a heat shield rubbing against the drive shaft? Could the sound seem to me that it’s coming from the left rear because it’s emanating through the chassis from elsewhere? Dunno…

[milarsky]

I know it sounds crazy but check all 6 fillister head screws connected from the rear differential to the output shafts. Mine had loosened over time and made a terrible sound.

[Syndrome]

Thank you! Nothing is crazy at this point. Do you know what’s involved with the differential rebuild and if it’s something a home mechanic can do (and has done)?

[milarsky]

I don't. That said, grab one of the output half shafts and gently pull up and down. There should be no play whatsoever. There will be play from left to right, so only check for up and down. If there is snug them up for sure.

[ahab]

Have you peeked at the fluid level in the diff? Maybe start by changing it.

[Machtig]

Check the driveshaft center bearing. Had an E39 M5 that would make weird noises from the rear of the car and turned out it was the center bearing.

[Dionk]

Hi - new owner of Syndrones M5. Source of the sound has been identified, It was a completely failed CSB. This allowed the replacement driveshaft to be hanging down and rubbing on the heat shield producing the sounds described above. Repairs and driveshaft replacement underway. V/R Dionk