is this a torsen diff?

[BMW_E30vert]

bought this diff which came off a 2.8 z3 1998, i believed its a torsen now im not sure heres some pics:





it has the infamous R stenciled on the casing and here are the numbers found on the internals although nothing shows on real oem once entered:

4061006592
701965
S40 AS
S25 AZ

My first thought was it's a torsen, if you turned the input flange both outputs would turn same direction but if you held one output you could turn the other in the opposite direction. i read torsen diffs act like open diffs until torque is applied.
After opening the rear cover im not so sure as it looks like a clutch type lsd, im confused

can anyone tell by looking at the internals???

[Motorhole]

It looks like a clutch pack to me too from what I can see in your pic. What did the backplate look like?

[maxfield]

Looks like it to me mate.

[BMW_E30vert]

back plate was a standard z3 backplate the one that looks identical to the e30 ones

[HairyScreech]

Funny this should come up, I have just done something similar for a compact track build, was under the impression they were all torsen type but it looks just like yours and i think i can see clutch plates in there if I look deep.
It does however turn opposite if you turn just one flange, had me worried for a while until I opened it up.

[BMW_E30vert]

i think its a clutch type from that picture motorhole posted, does this mean this is the same as the z3m diff? does anyone have a z3 torsen diff to compare?

[Motorhole]

Was just thinking about the backplate as the Z3M and E30 M3 backplates are different from all the others, with a protruding cluster of cooling fins at the bottom.




Gareth (member on here) might know. Also, DanThe has a torsen diff in his track car iirc, he might have an idea.

[Brianmoooore]

i think its a clutch type from that picture motorhole posted, does this mean this is the same as the z3m diff? does anyone have a z3 torsen diff to compare?

I have a torsen Z3 diff., and there are several bits of fusilli visible through the apertures in the diff. cage, as in the pic. above comparing the three types. Rear cover is very similar to a normal E30 diff.

[HairyScreech]

Cover on ours is as per e30, so much so that if you didn't know it was an z3 diff then e30 would be a first guess.

[BMW_E30vert]

Found some info which explains the different types of diffs found on the z3m BMW's apparently the one i have is rare as it has 40/25 lock
not sure how it found its a way into a standard z3' heres the link:

http://www.r3vlimited.com/board/showthread.php?t=224606

[HairyScreech]

hmmm, interesting.
I wonder if it's an options box ticking thing.

[DanThe]

I have one of these tucked away too
That R3V thread is probably the best way to explain it, no/less lock when lift off, not that ive driven with it but a mate has a built LSD in his race car that behaves the same way.

[Brian28]

Viscous/torsen type are awesome diffs on a race/track car, zero lock when you don't want/need it, variable up to 100% lock when needed. I have a 4.1 on my racer, and a 3.91 (rebuilt by diffmeister Gareth) from my brothers that will be for sale soon.

[bss325i]

Was just thinking about the backplate as the Z3M and E30 M3 backplates are different from all the others, with a protruding cluster of cooling fins at the bottom.




Gareth (member on here) might know. Also, DanThe has a torsen diff in his track car iirc, he might have an idea.

E30 M3's do not have that back plate with cooling fins.

Only Z3M's do.