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Old 01-19-2009, 05:56 AM   #1
FMD
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Default 3.91 e30 318is small case diff

I got a 3.91 small case lsd from an 85 318 (e30), this model had the M10 engine.

The bolt pattern (4 bolt holes on the top) on the diff should be a perfect match with the subframe of the ti and other e30s, right?

People have done swaps with the medium case diffs from 325 e30s with them bolting right up the subframe from what I understand... what's different about the M10 e30??

Any one have any input regarding this?

With the the 2 forward-most holes of the diff bolted to the subframe and the rear-diff bushing bolted in, the middle 2 bolt holes are off by 3/8 of an inch.

Is this well-known or did I just screw up or what?
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Old 01-19-2009, 07:05 AM   #2
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Yeah this doesn't make any sense...

I searched on realoem.com and it says the rear subframe part numbers for the 1985 318i (small case diff), 1991 318is (small case diff), 1985 325e (medium case diff), etc. basically the e30s all have the same subframe... Therefore, the bolt patterns (where they mount to the subframe) on the diffs should be identical and can be interchanged with this respect.

Also, people on this forum have not reported any issue with swapping the medium case e30 diff into the ti or have any problems with aligning the bolts of the diff with the subframe.

Therefore, the small case diff from a 1985 318i should theoretically have no problems with mounting onto the subframe.

Yet there's around a 8mm spacing difference between the carrier bolt pattern of the diff and the subframe holes.

wtf? Is this some kind of mutant diff or something?
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Old 01-20-2009, 02:40 AM   #3
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Mounting holes in the subframe were augered out to match the diff bolt pattern. Problem solved.
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Old 01-28-2009, 04:17 AM   #4
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Wow 3.91 is a little high isn't it?
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Old 01-28-2009, 05:44 AM   #5
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It's not so bad. I live in Seattle so most of my driving is pretty short distance. Its true the gears are really short but should make it easier to break the wheels loose at a moments notice which was the intended goal.
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