Z3 Torsen LSD into an E30?

[drzhivago1965]

I’m thinking about swapping a Z3 rear diff into my 89’ 325i automatic. I’m looking at the Z3 because they are Torsen LSD (vs. clutch pack). From what I’ve read, Torsens last practically forever. Only problem is that the lowest Torsen gear ratio I can find is 3.63. I currently have a 4.10 open diff (stock), in my E30. My question is if I can swap the 4.10 gear and pinion rings from my old diff into the Torsen to make it a 4.10 instead of a 3.63? Both diffs are 188mm, so I think this would be an easy swap, but before I drop coin on the Torsen, I’d like to hear from the collective wisdom of the E30 community.

Also, whenever my slush box gives up the ghost (I’m in no particular hurry), I’d like to replace it with a Getrag 260. Do you think 4.10 is too low for normal street driving with a manual trans? Should I change to a 3.91 when that day comes?

Thanks!

[TobyB]

4.10 would be a bit high on the street- but fun.

I tried using realoem to find the answer for the torsen question,
but there aren't parts breakdowns for the z3 diff...

t

[drzhivago1965]

Thanks Toby. The guy on eBay (whose selling the parts), says they'll fit, but I want a few opinions from people who know what they're talking about AND don't have a financial interest in selling me their used parts!

I see your not that far from me - cheers!

[chadthestampede]

Not that it matters really, but I'm pretty sure the z3 torsen diff is a 3.64...I have one in my car with an m30 swap and it's a pretty good combo.

[drzhivago1965]

Thanks for the feedback. My other BMW is a 2001 Z3 2.5 manual. With the stick I can really get on the acceleration. Not sure how it would be in an automatic. Still wondering if the 4.10 ring and pinion gears will fit. Anyone have any knowledge on this?

[Preyupy]

It would be easier to transfer the Torsen into the diff you have. You would not need to set up the pinion depth or bearing preload. You would just need to move the crown wheel from your open carrier onto the Torsen and then set the side bearing preload and gear backlash.

[Varinn]

I'm fairly certain it can be interchanged. The internals are pretty similar and from what I've come across in the few diffs I've rebuilt the difference is when you get far into the longer gearing ratios like a 2.93 that things start to get a little bit of deviation.

Even then the difference is mainly in the offset of the ring gear and where it mounts to the carrier. I believe it is to account for the different tooth heights between the 4.10/3.73 range gearsets and the <2.93's. The actual physical dimension of a carrier on anything between the low 3.xx to the 4.xx range should be the same regardless of what mechanism is stuffed inside of it.

[RobDog]

I have a 4.27 torsen LSD from a Z3 in my auto mtech2 convertible and I like it.

[djjerme]

Yes, you can. We have built a few diff's using the torsen from Z3's and pulling the ring and pinion off open, stock e30 diffs.

[Wolfman]

Forget the 4.10 if you are putting a 260 in it at some point. 1st is too short
even with 3.73.

[TobyB]

...but, but... but, first is kind of a throwaway anyway. And the 2-3 gulf is wide....

so, like the OP, I just give up on the lower gears, and set 4th for fun acceleration,
and 5th for a compromise between relaxed cruising (not with a 4.10!) and useful grunt...

t

[jeffnhiscars]

I have a 3.46 torsen in the eta. It's from a 00-02 z3 1.9 w auto trans

[djjerme]

...but, but... but, first is kind of a throwaway anyway. And the 2-3 gulf is wide....

so, like the OP, I just give up on the lower gears, and set 4th for fun acceleration,
and 5th for a compromise between relaxed cruising (not with a 4.10!) and useful grunt...

t

That's why you just put a ZF behind the M20.. (shhhhh... don't tell anyone!)

Surprisingly, I still have the 4.10 in the car. That's how we ran the last Lucky Dog race at the end of the season last year. I thought with the 1:1 final we'd be zinging the rev's but the motor was in it's happy spot..

[TobyB]

Yeah, I did that dance quite a bit with the 4 speed in the 2002-

often, the faster lap is where you get up to speed faster, and then maybe
the engine's turning faster than 'optimum power' by the end of the long straight,
costing you ultimate top speed, but since you got more 'area under the curve'
you still got there sooner.
Yeah, real racers have simulation divisions to nail this exactly, but at the Luck Dog level,
it's fun to just try it and see.

t