Cars / e32 / Driveline & Transmission / Large vs. Medium Case Differential Swap

Large vs. Medium Case Differential Swap

Article by: Don Gale

Article applies to: all e32 and e34 models.

I took some detailed dimensions noting the differences between a large e32 diff vs. medium case e34, for my friend Andrew, who has also has a boosted e32 735i 5-spd:





Note: medium case axle hubs may come in either small or large diameters. Large case axle hubs WILL NOT swap with medium case axle hubs, but medium case small hubs WILL swap with medium case large hubs.

Also note that medium case input hubs WILL NOT swap with large case input hubs. A medium case manual input hub might have the same stud size and bolt circle, which would work, but the splined pinion shaft on the large case is a larger diameter than the medium case and will not swap.

Editors note:

In my 1991 e34 535i, I swapped out the stock medium case (open) 3.46 diff for a medium case 3.91 LSD from an e34 M5 (US). In doing that, you’ll need a drive shaft from either an e32 7 series, or e34 M5  (these models use either a medium or large case diff with the larger diameter input flange with 10mm studs). If you It is possible of course to replace the input flange on the diff and go with one from the 535i (small version with 8mm bolts) if you don’t want to modify or swap your 535i driveshaft. Also understand that the splines for the CV joint on the back of the driveshaft are specific often specific to the model. For example, the 540i driveshaft splines *are not* the same and will not match on the stock 535i, M5, or 540i driveshaft. You cannot easily interchange front / rear half shafts on within these models as the splines are all different!

~ M. Oswald

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