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

The penultimate part of the M140i upgrades series takes a look at the clever and effective polyurethane Powerflex void filling inserts for the rear subframe and diff.
Apologies for the delay in this video, the footage was lost and then happily found. :-)
For those interested in the bushes, the parts are as follows:
Rear Subframe Front Bush Insert PFR5-1920
Rear Subframe Rear Bush Insert PFR5-1921
Rear Diff Front Bush Insert PFR5-1927
Complete replacement bushes are available for those seeking a more dramatic improvement that are less worried about trade-off in comfort (NVH) and/or those that use their cars primarily at the track.

[@Senninha1960]

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.)

[@vollcare4076]

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

[@CIRCUITDRIVERCARS]

Cheers mate 🙌

[@johnshaw8013]

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!

[@DjNikGnashers]

Thanks for another informative video matey.

[@CIRCUITDRIVERCARS]

Cheers Nik, shame it took so long. Glad to have restored the footage. 👍

[@dobbyboy3116]

Great review! looking at both inserts and the brace.

[@CIRCUITDRIVERCARS]

Glad it was helpful!

[@coenwag]

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.

[@AH-jv5zt]

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

[@CIRCUITDRIVERCARS]

When you drive them back to back with standard or more standard cars you realise what a difference all the parts have made as a whole. Even if some of the improvements like these are quite subtle. 😊

[@AGM240i]

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

[@daysofgrace2934]

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...

[@MrLIVELINESOLUTIONS]

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 :)

[@vollcare4076]

What’s your issuer with these Millway street camber plates ?

[@CIRCUITDRIVERCARS]

I should start a Patreon/Go Fund Me for an M2C! (Jokes! 😅) Is it the noise from the plates that are causing you to want to swap them out? They seem to be so hit and miss, with even individual parts changing through their life let alone different units. I’m really not keen on them on the road now, especially where there’s an alternative, so the hubs sounds very appealing, albeit likely expensive. I always thought a fixed, rubber bushed aftermarket top mount, available with say -0.5* camber would be a really good mod, I even approached a suspension company about them, but they weren’t able to help.

[@Poontang123]

Hello Who fitted the diff please need a reputable installer cheers

[@paulhein64]

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?

[@MrAshLloyd]

Noise harshness and vibration

[@martinlee7706]

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

[@CIRCUITDRIVERCARS]

Which bar/bars did you go for Martin?

[@martinlee7706]

@@CIRCUITDRIVERCARS H&R purple ones front and rear on my M140i Arran Senior (senior perform) fitted them ....