What is normal operation of M differential?

[JJM335]

I have on 08 E92 6MT without tech package (no MDM)...not sure if that makes any difference.

During a recent tech inspection I was shown that the rear wheels spin independently. Certainly not normal for most LSD's, but I asked if that could be due to the electronics in the diff. A few phone calls later I got the answer that the diff will not engage unless that car is running and there is load. Further, that the only way to really test it was to do some burnouts. So we did and I was never able to lay down 2 visible tire marks (straight line from standing start or around corners).

My question is how can one test the diff to see if it is functioning properly?

[Vic311]

Correct..the LSD locks up only on acceleration..(it doesnt lock up 100%.... ~ 90% upon acceleration)..and 50% on deceleration..

[JJM335]

Thanks for the quick reply.

So, unless I am doing some drifting, I probably won't notice both wheels spinning very often? Especially with track wheels/tires I imagine.

I'd still like to know how a service tech is supposed to test the thing.

[cposk]

Hmm I'd test it by doing a launch on wet pavement and having a person on each side of the car watching the back wheels. Both side should be spinning.

Are you having traction issues?

[JJM335]

Not that I know of, but I have no idea if I started this way and just have no point of comparison. It seems to be way to easy to control (especially in a drift) not to have some kind of activity going on back there.