Diff & rear subframe bushings - how stiff?

[jledford]

I'm working on a complete bushing refresh for the rear of my M3. I've got all of the new OEM style control arm inner and outer bushings and am now looking at the rear subframe and diff bushings to complete the set before installation.

From all my research on the BMW forums it looks like the AKG bushings are the way to go for both locations. They seem to have the best track record and it seems that a lot of E36 owners have issues with the PowerFlex or UUC rear subframe bushings.

This is my daily driver and while I don't mind added NVH I don't want anything that will feel like I threw solid aluminum in the car. My E30 had the purple PF subframe bushings and the black (hard) PF diff bushing and was completely tolerable for me on the street.

AKG has 75D (performance/race recommended use) or 95A (street use) diff bushings. Then they have 75D (race use only) and 95A (street/performance use) rear subframe bushings. The recommended use for each one is from their website.

So the question is how stiff of a bushing do I get for each location?

Do I go with 95A or 75D all the way around?

Or 95A subframe and 75D diff bushings?

Or 75D subframe and 95A diff?

Lets hear some opinions!

[e30Racer]

I have a full set of the 85A rear subframe, trailing arm, and diff bushings waiting to go in the white e30. I want a "basically" stock-type ride but with the added longevity of polyurethane. If I were in your shoes, I would go with the 95A as it's still a daily driver and would give an upgrade in performance, but not make the ride terrible. We have the 75D bushings in the race car and they made for a substantially stiffer ride over stock rubber bushings.

[nicktcr]

Solid is the way to go. All that deflection ruins your purdy alignment.

[HPEVOX]

My front motor mount is a 90A poly and it's drastically different than the stock rubber mount. Do it!

[kilgojr]

Agree with Mark.

[Chuck Baader]

Aluminum all the way. The only thing that should move is the suspension arms...as said, anything else dynamically changes your alignment. That said, the 75D urethane is a good substitute for the street...but note, that is the same hardness as Formica!!