1. I've been told that the percentage lockup in any given limited slip differential is related to the stock engine torque. Thus, a 25% differential paired to an e36 M3 engine should transfer about 25% of 238 (stock torque) = approx 60ft/lb before it starts to slip. On my ti, that seems to hold true, I can put a torque wrench on the hub and it will slip at a little over 30 ft/lbs, (127ft/lbs stock tq).

Is this just hooey, or true? If true, how do you measure if your differential is worn and slipping too early. E.g. if not that, it's 25% of what? I have dreams of an M Coupe / Roadster torsen diff, which on my car (by the above logic) would be closer to 60% locking...

2. Any good writeups on changing the oil in the diff? The LSD in the ti was dripping after the last track day (Laguna Seca) but hasn't dripped since, autocross inclusive. I was thinking my fluid was probably foamed up from pounding T11 hard repeatedly, perhaps just leaking out the vent hole and (hopefully!) not permanently damaged.

Thanks!

Bump!

Thanks Dave.

Fillip's link reminded me of unofficialbmw.com, where there are links for all kinds of proceedures.

I got the fluid changed to M1 synthetic 75 x 90, and the torque-wrench-in-the-bolt proceedure now shows about 65 ft/lbs, more than twice the torque than before until the wheel slips. I guess I'd been giving it a- beatin' on the track! The oil that came out of the diff stank too. :95

Also, the bushing that holds the diff to the subframe has seen better days, I guess you don't need an I6 to give that a workout either.

But if anyone has any info on the first question, that is, when an LSD transmits 25% of torque, exactly what that's referring to, I'd appreciate it.

Does it depend on the type of LSD?

Go here:

http://auto.howstuffworks.com/differential.htm

That should answer most of your questions.

Sorry, I lied...they've changed the format of HowStuffWorks.com and it looks like they've dumbed down the differential section from what I remember it being. Try a Google search, as I'm not exactly sure how to answer your question.

Here's a great page I found when searching for info about Quaife diffs.

http://www.houseofthud.com/differentials.htm

Dave

I suppose the real question would be how to tell if the durn thing is shot. I'm assuming that in the middle of my track day, the diff fluid was mostly foam so it wasn't working that well, but just on the street there's a minor difference with the new fluid. Racing it's probably a major difference...we'll see.

Any other ideas, I'm all ears...

Thanks!