http://forums.bimmerforums.com/forum/showthread.php?t=1565138

e36 lsd internals fit into e21 case
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I finally got around to tearing into my 168mm e36 lsd. Upon attempting to simply swap the e36 internals into the e21 case, it was obvious that it just wasn't going to fit without modification to either the case or the lsd unit. The opening of the e21 case isn't as wide as the e36 case. I didn't want to modify any of the moving parts, so I figured the only way to accomplish the goal was to grind away the portion of the case that was preventing entry of the lsd unit and ring gear. Here are some pictures.


Left: e36 Right: e21

I cut off the speedo sensor wheel on the e36 unit.

The opening on the e21 diff (right) is smaller than the e36. On the e36, the lsd/ring gear unit can be inserted straight in. With the e21 case, the unit must be inserted non ring gear side first, then rotated. A small amount of the case needed to be removed to allow the ring gear to clear.

I started by grinding away at the already recessed portion in these pictures. This is on the ring gear side of the diff. The ring gear just wouldn't clear this part. I ended up removing almost 1/8" of material, a little bit at a time, until I had enough clearance.

I was concerned that the large o-ring on the side cover wouldn't make a good enough seal with this amount of material removed, but I test fitted the side cover, and it seems to be fine.

LSD unit with ring gear installed with both side covers on.

NOTE: side covers must be from a non-lsd e21 diff. The LSD side covers are wider, and will not work.

Now that I know it can physically fit, the rest should be easy enough. I'll have to swap pinion gears. I'll be getting all new bearings, seals and o-rings. If I have problems with gear mesh, I'll have to acquire some new shims, but I have all winter to pick at it.

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Update:

I pulled the pinions from the e36 and e21 diffs. I measured them with a digital caliper, and all measurements were within .001" They are interchangeable.

e36 pinion: left
e21 pinion: right

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http://www.bmw2002faq.com/component/option,com_forum/Itemid,50/page,viewtopic/t,373426/




big difference in size and mounting points
Im going to run it upside down to give me more oil capacity sit flat to the mount I have in mind and just needs breathing hole made else where with a little filter of some kind.

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Oh d now your just reading me.

I don't want to.swap internals around so if e21 LSD easy to get IM willing to see if can mate 1600 shafts to those flanges. They only look like steel so could be drilled and tapped to 4 bolt shafts. Also would need to work out how to reduce size of the centre bores to hug the 1600 shafts.

Easier than custom stubs on a Subaru LSD.

e21 lsds are not common hence the swap to the later ones which is great that it can be done so easily. The LSDs are in almost all bmw e30 big 6 sedans and coupes I come across at wreckers. They are heavy diffs hence the use of the lighter compact e21 casing as a choice for weight reduction & modular mounting design.