small/medium diff interchangeable?

Mon Sep 21, 2009 12:19 am

I have a 318is which currently has a small case diff. Is the larger case diff a straight swap or what is required for this please?

Mon Sep 21, 2009 12:34 am

Why would you want one?

Mon Sep 21, 2009 12:44 am

Yep, straight swap as the width of the diff is the same so no difference in half shaft lengths and the prop can slide forward on it's splines at the center bearing for the extra length of the diff.

6potpower wrote:Why would you want one?

Easier to get an LSD and rebuild them as well as the small case diffs tend to break the odd time.

Mon Sep 21, 2009 1:00 am

I'm using the car for drifting and have destroyed two small case diffs, I reckon the medium size would stand up to the abuse better. Thanks for the info.

Mon Sep 21, 2009 3:18 pm

Yeah, any E30 apart from ones powered by a sewing machine M40 break the small case diffs easy enough with abuse.

Try look for a 4.45 as it'll make pulling 3rd much easier with the iS.

Look for the cwp from an early M20 E34 520 or automatic 525i or some of the E28s.

Then put it into an E30 large casing.

Tue Sep 22, 2009 7:12 pm

Are there 2 sizes of diff casing or three? I know I have a small case but from this advise I either want a medium or large case for the drifting.

Tue Sep 22, 2009 7:20 pm

there are three sizes of BMW diff but only two are used on E30's, small and medium case. the 'E30 large case' is technically better described as a 'BMW medium case'