Diff Bushings

[9kracing]

I'm about to put in solid subframe bushings.

I'm making somewhere around 500HP.

Are OEM diff busing going to be good enough, or should I just deal with some gear whine and go with poly?

Also why does AKG say that the subframe and diff bushings have to match?

[Slideways]

Stock diff bushings are already pretty solid. I'd rather replace them every 100-125k than deal with diff whine.

[oceansize]

I'm about to put in solid subframe bushings.

I'm making somewhere around 500HP.

Are OEM diff busing going to be good enough, or should I just deal with some gear whine and go with poly?

Also why does AKG say that the subframe and diff bushings have to match?

Go solid in subframe and OE in diff, minimal gear whine if any. This is the way.

[MathewM3]

I am running AKG diff bushings and the rest oem. No issues or whine.

[9kracing]

I am running AKG diff bushings and the rest oem. No issues or whine.

Correct. You'll only get the whine with solid or poly subframe bushings, plus solid or poly diff bushings.

My concern was having the OEM bushings get torn up after a few thousand miles. Is anyone else with a high HP car using OEM differential bushings and solid subframe?

[tlow98]

Correct. You'll only get the whine with solid or poly subframe bushings, plus solid or poly diff bushings.

My concern was having the OEM bushings get torn up after a few thousand miles. Is anyone else with a high HP car using OEM differential bushings and solid subframe?

The OE bushings have extremely little amounts of damping material in them. Which means very little play overall. Even in tracked cars it seems age is the main failure mode.

Unless you’re planning to shift extremely hard and apply violent loading/unloading (drifting, drag racing) I doubt you’ll have an issue with the OE diff bushings. They’re pretty stout. This was never a failure mode back in the HPF car era. Those were often 600hp+ cars. They’re just getting old and rotting apart.

I’d replace with new genuine parts and not think about it again.

.02

[Ramps]

Go solid in subframe and OE in diff, minimal gear whine if any. This is the way.

This is, in fact, the way.

[9kracing]

OK! OEM it is.

If I have to replace the diff bushings in 5K miles I'm sending y'all a bill

[PSUEng]

My OEM diff bushings, at 80k just rotted away. Replaced with stock, feels great. They just rot over time. What tlow98 said above is spot on.

The longer I own this car, work on it in my limited capacity, read, engage here on this forum--BMW made a race engine and driveline, put it in a series car (as much as it is) and only in the last few years we are realizing the maintenance this chassis really requires to run as they get up there in age; some good things and some bad. I think it's a great car, and I'll keep mine indefinitely as long as BMW keeps parts available. Unfortunately, there is a cost to it all.

[maw1124]

I've done diff bushing with OE, no complaints, especially if it takes another 15 years for them to go. Who do we like best for subframe bushings as an improvement over stock?

maw

[Estoril]

OE on both my dedicated track and street M3s. Zero complaints or issues.

[0-60motorsports]

I did Solid CMP Subframe bushings with OE Diff Bushings in place and diff whine has gone up a little bit.

[Obioban]

I've done diff bushing with OE, no complaints, especially if it takes another 15 years for them to go. Who do we like best for subframe bushings as an improvement over stock?

maw

For a street vert, I'd just do new stock.

For a performance upgrade, with a minimal but present NHV penalty, the CMP solids are hard to beat-- they raise the subframe to partially counteract the suspension geometry lost from either adding subframe reinforcement plates and/or lowering the car.

[maw1124]

For a street vert, I'd just do new stock.

For a performance upgrade, with a minimal but present NHV penalty, the CMP solids are hard to beat-- they raise the subframe to partially counteract the suspension geometry lost from either adding subframe reinforcement plates and/or lowering the car.

Clear as a bell, as usual, thanks Ian. I'm not into NVH penalties on a car that is already a bit rattly (compared to my other cars at least). Obioban

I think this car is going to remain stock except for intake, tunes and stereo (maybe Dr. Vanos, Koni fronts). That's the unsurprising, sensible answer that keeps coming back.

maw