Rear differential- best place to source?

[WhiteE30ic]

Hey all!

1985 325 eta with an M50 and ZF320. Rear differential from en E28 with LSD and 3.73’s.

The car is a canyon carver/maybe occasional track day car. I don’t need to daily it.

The 3.73’s are just too short. 1st is almost useless and I am in 5th at about 45 mph (unless I’m driving hard). Highway speeds are well above 4k.

Looks like a lot of the E36 crowd goes with 3.25 and I know the M3’s had a 3.23. Could jump to a 3.46.

Anyway- I’m not having much luck sourcing a complete 3.25 LSD. Any tips on where/how to find one? I’m close to NorCal so should be able to find one.

I also considered buying a ring and pinion and having a local shop install it for me.

Thoughts on ratio or sourcing?

[AWDBOB]

Finding one out of a Z3 is likely your best bet. E28 3.25s are hard to come by these days. Also, extend your search to include 3.15s. Same recommendation for a 3.46. Both were E28/E24 ratios, not E30. Easier to find out of a Z3 than an E28.

An E30 S2.93 would also do the trick and are pretty easy to find. Use a gear calc to compare 2.93 to 3.25

[reelizmpro]

Yeah, Z3's are more common in the yards these days and you'll have a newer diff with Torsen or clutch LSD options as well. Look for a 3.15 diff out of a Z3 2.8 I believe. I have a 3.23LSD from an M roadster in my S52 swap car and it's short but not too bad.

[sna77]

Hey all!

1985 325 eta with an M50 and ZF320. Rear differential from en E28 with LSD and 3.73’s.

The car is a canyon carver/maybe occasional track day car. I don’t need to daily it.

The 3.73’s are just too short. 1st is almost useless and I am in 5th at about 45 mph (unless I’m driving hard). Highway speeds are well above 4k.

Looks like a lot of the E36 crowd goes with 3.25 and I know the M3’s had a 3.23. Could jump to a 3.46.

Anyway- I’m not having much luck sourcing a complete 3.25 LSD. Any tips on where/how to find one? I’m close to NorCal so should be able to find one.

I also considered buying a ring and pinion and having a local shop install it for me.

Thoughts on ratio or sourcing?

I had mine built by Diffsonline.com. They'll build you a LSD to your specs...

[82eye]

I had mine built by Diffsonline.com. They'll build you a LSD to your specs...

just don't get the fake ls center unit they use. make sure you buy a real one.

edit : maybe that's a racingdiffs product.





yeah, that thing.

[sna77]

just don't get the fake ls center unit they use. make sure you buy a real one.

edit : maybe that's a racingdiffs product.


yeah, that thing.

yes, wrong company. diffsonline has been around forever and you can fully customize your diff however you want...

https://diffsonline.com/collections/differentials/products/differentials-for-bmw-e30-325-m3

[WhiteE30ic]

Thanks for that. I’ve looked at diffsonline and considered that route as well. More money but you get what you want!

I may have a line on a Z3 unit @ 3.15. It would give me a chance to try the ratio before getting one built.

[82eye]

Thanks for that. I’ve looked at diffsonline and considered that route as well. More money but you get what you want!

I may have a line on a Z3 unit @ 3.15. It would give me a chance to try the ratio before getting one built.

if you like the ratio you could just get the ls unit and install it in the diff yourself if it's cheaper. rebuilt and swapped a couple around for gear changes and it's not too bad if the pinion is ok.

[WhiteE30ic]

Thanks all- found a nice 3.07 Torsen from FB marketplace. I’ll install this weekend. Now I will have a 3.73 if I want to track and 3.07 for street.