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LSD identification

Scott Buchanan <[email protected]>  ASKS:

I'm about the swap the 3.25 LSD on my '87 535is for a 3.64 LSD from an 
E30.  How can I be sure that I in fact get a limited-slip differential 
(used) and how can I verify the drive ratio prior to installation?

Secondly, will I need to have my speedo recalibrated due to the ratio 
change or are the two even related?

ANSWER:  LS Diffs usually have a big "S" painted on them and possibly on the id
tag.  Also, when rotating the pinion shaft, both output shafts will turn in the
same direction and you can not stop one from turning with your hand.

The speedometer on later BMWs are electronically triggered from a sessor mounted
on the diff.  This is counting the revs of the half shaft so a tire diameter
change will affect the sppdo but the gear changes are prior to this so they will
not.

Hope this helps
Bob
Many BMWs