Until the time comes for the big Randy Forbes dual-ear subframe upgrade, I've been wondering about my stock diff bushing: as I have upgraded my subframe bushings to I.E. urethane last year, should I upgrade my diff bushing as well? My current diff bushing is original, with 49K miles of spirited driving on it.

Just as too stiff a diff bushing could be detrimental to the single diff mount (additional torque stress), I would think too soft of a diff bushing would be detrimental as well, no? If the diff is allowed to move more freely with a soft bushing, that movement surely get's transfered to the diff mount as well? (This perhaps, in addition to poor welds, could explain diff mount failures on 1.9 Z3s?)

So, I've been looking into a happy medium diff bushing to match the I.E. urethane subframe bushings.




Turner Motorsport sells a delrin diff bushing, but Doug Mahar from Turner has told me that the I.E. urethane subframe bushings have too much compliance to run with the solid Delrin bushing and this would put too much stress on the rear diff cover. The only way to run the derlin diff bushing would be to run solid subframe bushings.




Another solution would be a matching urethane diff bushing from BMWBushings. They say that their bushing is 80-85 durometer polyurethane construction (similar to the I.E. subframe bushing construction) versus BMW's OEM webbed-diff bushing of 60 durometer construction. I've heard that this solution may not quite line up in an E36/8 application and is moreso E30 specific.




And, there is the VAC Motorsports diff bushing which may be the happy medium; it is solid rubber and may offer the best stiffness/flex characteristics.

Or, I can just forget about it all and stick with stock.

If I decide to go with an upgraded diff bushing, I'll probably have Edge Motorworks in Dublin, CA do it at the same time they'll be doing my oil-pump nut preventative fix (coming up soon).

Ciao,
Nivola 368s #92