There are many different options for picking the right differential. Some of these differentials are too high for highway speeds. Some are too low for fast acceleration. Many of these differentials (bolded) are featured in E30’s. Many of them can be grabbed from E28, E24, E32. Just swap the output flanges and the rear cover from that of your current E30. It’s as simple as that. I do not know the entire differential compatibility between BMW’s in the 80’s-90’s. Not to mention, it’s relatively out of the realm of the M60 swap, so here is a brief overview.
The gears in blue are all from the same family of shims and can be directly swapped if desired. Make sure that the shims are reinstalled in the same exact position or play can develop and decrease the life of the differential.
As per Table 18 The ones in Red all come from the same family of differentials and can swap simply the gears from one to another while reusing the current shims. If going to a shorter gearing in blue, new shimming is necessary and is not for a novice mechanic.
Table 18 E30 Differential Gear Ratios
|Too low IMO for driving. Revving really low on the hwy.
|Widely available in the 325es version. This would have been my second choice
|I would have preferred this gearing for highway cruising. Perfect for a highway cruiser
|Very good gas mileage hwy cruiser – Long shifting in between gears
|This is the gearing that I had and it was perfect – Slightly short on the hwy, good torque
|This has been used by other members and they claim it’s slightly too short
|Still on the short side for an M60
|Popular E30 ratio, but not for an M60