Originally Posted by brettski
It has been suggested that one way of converting an E38 open diff to a LSD diff, could be to use the limited slip center spool from an E32 seven series. Now there are are several questions that occur to me that may be of concern:
a) Does the LSD spool need to match up with the gearing ratio of the open diff?
b) How does the spool mount and integrate within the existing diff housing?
c) Where there any issues with the E32 LSD diffs that would make this a really bad idea?
a) The gear ratios should be the same to maintain identical performance. A higher ratio will make the car quicker off the line with a higher top gear cruising engine speed
b) From what I could tell by looking at realoem it seems that the differentials are very different and so are the casings. I would also be concerned with the output shafts being different and the driveshaft inputs being different as well. I'm not sure if this would bee possible without extensive modification to the rear end. I also believe the E32 had a "big diff housing" as well as a "small diff housing". I think thee 735i's and 730i's had the small diff and the 740i's and 750i's had the bigger diff. It might be possible that the "big diff" will fit in your 740i...
c) I doubt it as long as they were properly maintained.