diff fluid change

[mcoupe5/6]

hi all,

been reading around the forum abt this and have found a couple different answers. i am wanting to do a diff fluid change soon...i am hearing a groaning when making tight turns, with the car hot or cold. ( it seems louder now than it was a few weeks ago)
should i look for a fluid with the FM booster? the fluid ecs sells seems to have it in there.
how bad is that groaning and should i worry about it?

any info from ppl that have done this before is much appreciated!

[SCHMOUPE]

Originally Posted by mcoupe5/6

hi all,

been reading around the forum abt this and have found a couple different answers. i am wanting to do a diff fluid change soon...i am hearing a groaning when making tight turns, with the car hot or cold. ( it seems louder now than it was a few weeks ago)
should i look for a fluid with the FM booster? the fluid ecs sells seems to have it in there.
how bad is that groaning and should i worry about it?

any info from ppl that have done this before is much appreciated!

if it happens while turning, you sure it is not related to your power steering?

[mcoupe5/6]

It really seems to be coming from the rear of the car... I've read about the differential groaning in tight turns so I thought that could be it.

[StickMon]

I change mine every 30-35k miles.
I use the OEM champagne with FM booster. Never heard a peep out of the diff.
IIRC, the FM booster is specifically to stop the groan you're hearing.
Other's have said that the groan means it's doing what LSDs are supposed to do, and the FM booster stops it from performing correctly.
All I know is it doesn't improve the radio reception.

[mcoupe5/6]

That was my confusion as well...
But it would be odd for BMW to make diff fluid that renders the diff useless, wouldn't be very German of them.

[bignosejim]

You could also make your own fluid with friction modifier. It uses the OE fluid without FM and you add your own (Ford racing FM). I did this on my car the last time I changed the diff fluid. Here is the thread I started for that. If you want to add the least amount possible start with less and see if your diff groans then just add a little at a time until the whining stops. My diff doesn't make any noise, next time I'll use less FM.
The only downside to this is now ECS sends me offers for Mercedes Benz!