Do midcase diff from M20 Autos FIT THE 318IS?!

[WhatWentWong]

Hi all,

I am having issues fitting a midcase 4.10 LSD diff into my 318iS. It came off an 89 325i Auto. As far as I know, this is not an uncommon swap!

The curious thing is, it didn't completely not fit. It is missing the bolt holes by perhaps a 1/16" of an inch - and I measured the bolt pattern against my small-case diff and they turned out to be the same.

Apparently I need to shorten the driveshaft a bit to fit the bigger diff, but I seemed to have ran out splines on the driveshaft for length adjustibility, with about 1/16" left making all my bolt holes not line up.

Any insights? Do I need a new driveshaft?

[z31maniac]

4 cyl cars have the small case diff.
6 cyl cars have the medium case diff.

[Jean]

It should fit w/o any modifcations.

[SpecM]

It should fit w/o any modifcations.

-yep, it is a 100% bolt-on deal

[EN318isPDX]

Recently my LSD failed in my 318is! Here is a pic of the Medium case 325is LSD next to my small case LSD. It was a direct bolt on, no mods

[EN318isPDX]

Sorry for double post but heres a pic of the top of them.

[Danny]

Mine was bolt on as well.

[EN318isPDX]

After looking at my picture i took i noticed that the breather on my old LSD was completely clogged. I am starting to believe this is what caused it to fail. It did have 240k on it but I had replaced the gear oil with redline synthetic and shortly after i gurnaded.

[SpecM]

cool pics, thanks.

is there a differance between the gears' size in the small diff and medium or is the case just different?

[Rigmaster]

cool pics, thanks.

is there a differance between the gears' size in the small diff and medium or is the case just different?

gears are different size.

Medium case diffs have 188mm diameter ring gear, and are usually referred to as "188" case diffs. Can't remember the small case ring gear size, but I think the large case BMW diffs are called 210 - because of their 210mm diameter ring gear.

;)

[SpecM]

gears are different size.

Medium case diffs have 188mm diameter ring gear, and are usually referred to as "188" case diffs. Can't remember the small case ring gear size, but I think the large case BMW diffs are called 210 - because of their 210mm diameter ring gear.

;)

ohkay gotcha. thanks