E30 Open Diff: Swap Internals to LSD?

[MaxBell]

Hey guys;

I have a really good condition open diff in my car, but I want to swap to LSD. I have a 3.25, but I just want to swap the internals since the LSD's case is super rusty.

Can I just put the LSD in the Open Diff case? They're both medium case.

[Sagaris]

Yep, A friend did this on his e21.

I plan on doing the same to make an S4.10 out of my S3.73 and open 4.10 this winter.

In a nutshell:
Drain fluid
Pry the output flanges off
Unbolt the side covers
Remove rear cover
Remove diff assembly
unbolt ring gears and re-install the clutch unit with the desired ring gear (must return to the diff. case with the corresponding pinion gear of course)

http://e28-535i.com/upload/LSDReplacement.pdf

[e30leigh]

you need the pinion too i believe the ratio is made up of the pinion and crown wheel. they need to match

[Sagaris]

^right

You dont want to remove the pinion unless you want to learn how to / pay someone to do the lash adjustment so if you have an S3.73 and want to convert an open 4.10, you will want to put the LSD unit into the 4.10 case instead of swapping the 4.10 ring and pinion into the S3.73 case.

[Jaxx_]

And as I understand, the pinion and crown are married because of wear, so you can still not have a good mesh if you use a mix-matched, but same ratio, set of gears from two different diffs.

[Wanganstyle]

Also; the bearings and races are matched items; they wear in together

[MaxBell]

Ok, so I tried putting the S3.25 into the Open 3.73 case and it's a mess.

The side covers are too lose and there's a ton of play.
The ring gear doesn't even come close to the crown gear.

[e30leigh]

you have obviously forgotten something or your research was wrong.

[MaxBell]

It's ok, I'll just sandblast and paint the LSD.

[e30leigh]

dont get sand inside it :P

[Wanganstyle]

Yes, paint will solve the fitament issues

[e30rapidic]

I ran into the same problem when swapping an e36 3.15 R&P set to an LSD carrier/case from an 2.93 LSD e30. Made me wonder if the e36 gear ring gear is thicker than those of an e24/28/30 etc. anyone know if ring gears come in different thicknesses in certain ratios?

I've got 5 diffs now, all in various stages and boxes 2.93, 3.15, 3.46, 3.73 and 4.10 :-/

[Wanganstyle]

In Bmw 188mm diffs for e24/28/30/32/34/36

2.65, 2.79, 2.93, 3.07 all use one offset standard of LSD.
3.15-4.88 use a different geometry LSD unit.

One hopefully knows this before taking things apart.

The bolts and holes also vary; m12/14

[e30rapidic]

One hopefully knows this before taking things apart.

Nope but I do now, thanks. I searched for a long time but never found any info. Sweet.

[Varinn]

I've been wanting to do this for a while, I have a 3.73 open, a 3.91V, and a 3.25S. I want to put the 3.25 clutch carrier into either the 3.73 or the 3.91 but dont want to be forced into paying someone to set up the diff