M140i Upgrades // Part 8: Powerflex Bush Inserts - Rear Subframe & Diff Void Fillers 

A concise subframe understanding.... The subframe is held in place by bushings on the end of the axle, and the diff mount on the rear end of the diff. The subframe is NOT designed to hold the weight of the car! The weight of the car is transfered to the trailing arms/wheels by the shock/spring assembly. The subframe is only there to keep the trailing arms in place, resisting the sideways and accelerating/braking forces. (Of course the subframe/diff bushes do get some vertical forces to resist the resulting forces from the torque that is transferred to the wheels, these are a lot smaller than the force that the actual weight of the car would give.)

Great to have you (and the footage) back here 👍

Hi all, I have watched tons on videos on diff and subframe bushings. I took me quite sometime so decide which ones to fit. I went for powerflex full back ones and a powerflex purple diff bushing. There is zero diff whine!! The subframes now feels so much more connected. I high recommend. The noise is totally fine to live with, it’s a bit more like that sound that you have when you drive on really rough tarmac. That’s it.

It really is when all things combined together on these cars work in synergy with each other the little (big) things all add up.

Back in the day... 20yrs ago, I used to make solid Ali rear subframe bushes for the Nissan 200SX which I was heavily involved with through SXOC... They transformed the handling without being bad for NVH... miles better than poly bushes!

Thanks for another informative video matey.

Great review! looking at both inserts and the brace.

Hi mate. What do you reckon would be labour costs for front and rear subframe inserts? I'm being quoted 250-300 plus vat. Seems a lot. Thanks

antiroll bar is a MUST , u will feel not shaking while in sharp turns

Great explanation and editing. I have an M2 but have learned quite a bit from this. I recently installed the Millway Street camber plates and I am on the fence about keeping them. Maybe combined with the PS4S will make them more tolerable. I can get the -30' offset camber hubs from BMW to add back some negative camber. Please buy an M2 Comp and do a series on that so I can get some direct benefit :)

That what i notice compared to my 2009 Boxster vs 2005 120d; the rear of the 120d i can’t tell what going on, it doesn’t communicate. The Boxster tells me exactly what’s happening therefore i feel confident in pushing on. I’m getting the inserts done with SuperPro bottom mounts and PowerFlex rear top-mount bush. I’ve already got Koni FSDs, BMWP bumpstops and Eibach Pros on and changed the the rear and front top-mounts via the BMW repair kit. Next up will be changing to 1M/M3 LCAs and tension struts...

New to this and thinking of an LSD from my BMW dealer who have a special offer on and so was interested in the void fillers. Do you have a bit more info on the product please? Also what is NVH?

Does it help with the little bit off clunk from diff ?

Hello Who fitted the diff please need a reputable installer cheers