Diff swap

[2002maniac]

Problem: It won't fit. E36 diffs do not work on E30 subframes. I believe the only diff cover that does it the M-Coupe finned cover.

The E36TI uses an e30-based subframe as well.  The rear cover may be different, but it should swap over just fine.

4.44:1 is a bit radical

[tjts1]

Your car must be slow as piss with that 3.73 diff. with your M42. That is way too tall for the little torque it already generates. Definitely swap over that 4.10 LSD unit from your 325i.

M42 + 3.73 is definitely not "slow as piss".
http://www.r3vlimited.com/board/showthread.php?t=43069

http://www.r3vlimited.com/board/showthread.php?t=42732

In normal real world driving a 3.73 or 3.64 is faster. In my case I went from a 4.1 LSD to a 3.64 open diff and I love it for my daily driver. Its just as quick off the line but I don't run out of revs in first and second gear anymore. 4th gear is identical to my old 5th, and 5th finally feels like a true over drive. It made the cabin a much quieter place at highway speed.
 
The diff is held in with 4 bolts to the sub frame, 1 large bolt at the bushing, 6 allen screws for each axle swaft and 4 bolts at the prop shaft. The first time will take you a few hours and just like anything else, once you are familiar with the process it gets much easier and faster the second time around. Probably 1-2 hours tops.

Problem: It won't fit. E36 diffs do not work on E30 sub frames. I believe the only diff cover that does it the M-Coupe finned cover.

318ti and Z3 diffs are direct swap. They like to swap in medium case E30 LSD.
http://www.318ti.org/notebook/diff_conversion/index.html

[twinpop171]

I'm going to do a diff. swap as well.  My m42 has an open 3.73 in it and my '89 325i DD has a 4.10 LSD in it.  I want to do the swap but want to make sure that it IS a direct swap.

How can you tell the difference between a small and medium case differential?  I've done searches on this before but I have never really found out the answer.

Bump.

[tjts1]

All 318i/is had small case diff with 6 bolts on the rear cover. All 6 cyl and M3 cars had medium case diff with 8 bolt cover.


6 bolt small diff.


8 bolt medium diff.

[doucy2]

some if not all ti's came with s4.27's they bolt right up in a m42 but gearing is way to high it is awesome if you wanna race, but as soon as you get on the highway your pocket will hurt.

best diff's for the m42 (in my opinion) 1. s3.91  2. s3.73  3. 4.10

[tjts1]

All 318ti used a 3.45 diff for 5 speed manual (1 to 1 5th gear) and 4.45 diff on 4 speed autos.

[twinpop171]

Thanks tjts1 for the info.

As posted above by other members my m42 has the small case diff. and 325i has a medium case diff.  I guess I couldn't see the forest through the trees when comparing them before.  Good info.

Thanks, Dan.