Subframe and Differential Bushings Selection for Lowered 325ix

[Chebyshev]

I'm about to refresh my rear subframe this winter and install it in the spring. Mine is also on H&R lowering springs, what do you think is my best option for rear subframe bushings and spacers, etc for the diff? I'm confused about the geometry stuff.

[lefthookz]

I ended up using RWD subframe bushings, and using spacers in between the diff and the subframe to accommodate the shorter bushings. This way the geometry of the trailing arms is better but the diff is roughly at the height it is designed to be, putting less stress on the driveshaft versus just bolting the diff straight to the subframe as normal. I believe I am using 5mm spacers, they're basically just really thick washers. I'm still using the factory diff bolts to connect it to the subframe.

[vooak]

The simple way is to stack some washers on top of the diff between the subframe so the diff stays in the original position, and use a stock diff bushing (unless you like vibrations, I wouldn't bother with aftermarket - the original is already plenty stiff). Mine's been like that for almost as long as I've owned the car (19 years! Fuck me!). I think I used 2 thick washers which is about 3/8" - close enough to the difference in bushing length at least.

I wouldn't just put it together without any spacers, it's going to tweak the subframe, diff bushing, bushing bracket, or all 3 - plus you don't want to mess with the pinion angle.

Subframe height actually doesn't raise or lower the car - it keeps the trailing arm geometry aligned with the extra ride height. if BMW had used the regular RWD bushings, the rear alignment would have positive camber and toe out. So by using the shorter bushings on a lowered ix, you automatically correct issues with negative camber & toe in from lowering the car, without needing adjustable trailing arm bushings.

Oh, there's a metal washer/spacer thing that you need to keep at the bottom of the subframe bushings. The bottom bracket that holds the subframe in place is a little different, if you don't make up that gap the brackets will be bent when you tighten the subframe bolts, or the bushing will move around because it won't be compressed fully by the bolt/bracket.

Hi, when you say use stock diff bushing, you mean stock bmw exentric diff bushing from ix? Or can I use original stock normal e30?

[packratbimmer]

If you are using stock RWD subframe bushings to move the subframe closer to the car's body, then use a stock RWD differential bushing in the differential cover. iX subframe bushings move the subframe away fom the car's body, so the differential bushing has to have the hole higher to compensate.