E28 Diff Swap on a 318i

[wildstoats]

Ok. I'm in the process of swapping diffs on my '91 318i and I just want to verify a couple of things. I am planning on using a 3.25 LSD (medium case) from my old e28 so I have already swapped the rear cover to a medium case e30 cover. Now I'm curious what to do about output shafts. The e28 output shafts will not match up with the 318i axles so I was thinking about swapping the output shafts from the old 318i small case diff into the e28 medium case. Will this work? I test fit them and they went in fine but I want to make sure this is going to work before I get the car back on the ground.

I also test fit the diff and it seemed like the holes were not lining up correctly. I measured both the diffs and it seems like the holes are at the same spacing but I just wasn't sure. I know getting the diff bolts on can be tricky but I just wanted to check and see if there would be any reason that an e28 diff wouldn't clear on a 318i.

Thanks a lot in advance guys!

[twistednut]

That 3.25 ratio is way low for a 4 banger. I put a 3.73 in mine an it struggles going up over some hills.

[wildstoats]

Ah, my bad, I forgot to mention it is an m30 swapped car.

[wildstoats]

Bumpy

[Teaguer]

Figured you had it figured out by now.

Yes the 318 stub axles will pop in and work.
Yes the diffs will mount the same using the same holes.
Get it in already !

[FredK]

You must use E30 medium case stub axles. The small case stub axles are too long and will not work. I ran a 3.25 in a 318is for a few months, and I had to use the medium case stub axles from a 325i.

[Teaguer]

You must use E30 medium case stub axles. The small case stub axles are too long and will not work. I ran a 3.25 in a 318is for a few months, and I had to use the medium case stub axles from a 325i.

Really ? I did the same and could have sworn I used the 318's stubs.
The again I had 6-7 diffs around and could have ended up using whatever. :drink:

[wildstoats]

Yeah I was a little confused because the small diff stub axles pop right in and I spun it a little just to check for binding and everything looked ok but I wasn't sure if I would run into problems down the line if I tried to frankenstein them together or not. I'm still not exactly sure what to do about it. Do you think I should just try to scrounge up some 325 outputs to be on the safe side?

[Teaguer]

Yeah that is what FredKsan is saying.
Find some M20 stubs and go with them.