UHMW vs Poly Subframe & Diff bushing e82

[elias 253]

Looking into replacing my rear subframe bushings soon and thought Id better do the diff ones too to match. Looking at either the Condor speed shop UHMW ones or the AKG motorsport 75Dpoly bussing. Anyone had any experience with either of these? My stock bushings feel very sloppy, all the more noticeable after installing firmer suspension. Car isn't daily driven, but will still be street driven.

UHMW:

https://www.condorspeedshop.com/collections/1-series/products/the-crucial-e8x-subframe-differential-mount-combo

Poly:

https://www.akgmotorsport.com/product/rear-subframe-bushing-set-for-bmw-e90-polyurethane-75d/

Cheers 

[jon dee 500]

Quiet night so why not post an answer to a question that was not asked   I'm not familiar with the bushings in question or the forces acting on them. If the loads are pure compression then either of the bushes you have linked will do the job. However, if the loads involve impact, twisting or rotation increasing the stiffness may transfer forces and induce binding or bending into other suspension components. Rubber bushings typically add spring rate to suspension arms and operate without lubrication. UHMWPe is self lubricating but urethane requires lubricating when used in pivoting joints, and neither add spring rate. 

Just to provide a basis for endless debate, here is a small chart with my comparison of the NVH effects of different types of rotating bushes used in suspension arms...

Entirely subjective as NVH will vary with suspension design, bushing hardness and whether the vehicle has the full factory interior or if it has been gutted etc. If suspension arms only have movement in a single plane then hard bushing are fine, but if the arm "twists" as the suspension travels through its range of movement, the OEM rubber bushings may have been designed to absorb the twist. If that is the case, then hard bushings will transfer loads into the chassis or subframe, and these forces may be strong enough to break welds of tear metal brackets. 

Probably an irrelevant post, but if I wasn't typing this I would be shaving my legs and getting ready for a night on the town   

Cheers...

 

[elias 253]

Appreciate the reply @jon dee some good information in there. From what I can tell, poly bushings in the subframe shouldn't need lubrication as there should be minimal twisting, compared to something like a control arm. 

The main reason for changing the subframe bushings is the fact that im trying to get rid of the vague feeling rear end which has become all the more noticeable since having installed aftermarket suspension which is significantly stiffer. Installing bushings which do not have a spring rate would be ideal I think, as this would eliminate the current situation of essentially having two spring rates, one from bushing and one from the springs, where it seems currently the bushings are softer which is a very odd feeling.

From my research it seems, tearing of welds/chassis only becomes an issue on high hp cars with solid aluminium bushings, as UHMW and poly seem to be soft enough to absorb enough of the forces to not crack anything.

In terms of NVH, car does still have full interior and will keep most of it, so that is something to keep in mind...

 

cheers

Edited June 3, 2022 by elias

[M3AN 4016]

Have you considered poly inserts for the stock subframe bushings? They are significantly less expensive than either of the options you've posted and might get you what you want.

For example:

https://www.bimmerworld.com/Suspension-Steering/Subframe-Bushings/Powerflex-Rear-Subframe-Inserts-BMW-E90-E92-E93-gas-E80-E82.html

https://superpro.com.au/find/superpro-subframe-bush-kit-for-a-superpro-suspension-parts-and-poly-bushings-for-bmw-1-2003-2013-e81-e82-e87-e88-/productnr-SPF3944K/cid-999500350/vid-

Edit, more:

https://www.fcpeuro.com/products/bmw-suspension-subframe-kdt918

On special: https://www.nolathane.com.au/product_detail.php?part_number=49203

IIRC mine were about NZ$120.

Edited June 4, 2022 by M3AN

[jon dee 500]

I worked with a guy who had some kind of BMW racecar and I know that he was forever repairing / bracing rear subframes.  Seems to be a well known issue with certain models but I don't have any specific details. Obviously there are issues with IRS that don't exist with live axle vehicles, and there is likely to be a lot of information on the causes and fixes posted on BM forums around the world. 

Solid bushings are the ultimate fix for racecars, but are not recommended for any car that is used on the road. Compromise is the name of the game if you need to drive to the track. So as suggested above, poly bushes may do what you want. Just make sure to get quality bushes from a reputable manufacturer. Good luck

Cheers...

[Sammo 2544]

Have you replaced your RTABs? Could be a real factory on a sloppy rear end.

From what I’ve read, generally poly subframe bushes won’t add much NVH at all but diff bush may do.

I would go 80a poly as an in between - I’ve got an 80a diff mount on the way for the E30 (mainly for simplicity of installation) and when time comes I’ll go with factory rubber RTABs and 80a poly subframe bushes.

[elias 253]

Thanks for the replies, much appreciated.

On 6/4/2022 at 11:58 AM, M3AN said:

Have you considered poly inserts for the stock subframe bushings? They are significantly less expensive than either of the options you've posted and might get you what you want.

For example:

https://www.bimmerworld.com/Suspension-Steering/Subframe-Bushings/Powerflex-Rear-Subframe-Inserts-BMW-E90-E92-E93-gas-E80-E82.html

https://superpro.com.au/find/superpro-subframe-bush-kit-for-a-superpro-suspension-parts-and-poly-bushings-for-bmw-1-2003-2013-e81-e82-e87-e88-/productnr-SPF3944K/cid-999500350/vid-

Edit, more:

https://www.fcpeuro.com/products/bmw-suspension-subframe-kdt918

On special: https://www.nolathane.com.au/product_detail.php?part_number=49203

IIRC mine were about NZ$120.

I decided against the inserts as I believe my bushings are too worn for these to work as intended and with my stiff coilover setup I think id still have too much movement, and don't really want a second spring rate (from the rubber bushings)

On 6/4/2022 at 12:31 PM, Sammo said:

Have you replaced your RTABs? Could be a real factory on a sloppy rear end.

From what I’ve read, generally poly subframe bushes won’t add much NVH at all but diff bush may do.

I would go 80a poly as an in between - I’ve got an 80a diff mount on the way for the E30 (mainly for simplicity of installation) and when time comes I’ll go with factory rubber RTABs and 80a poly subframe bushes.

I haven't replaced the RTABs yet, will do the subframe bushings and see if there's still slop, if so, then those will be next, we will see.

 

I ended up going with the Condor speed shop UHMW ones, as the company was great to deal with, and very prompt in answering any questions as well as hearing some positive reviews. Will update this thread once I get them installed, should be here in about a week, shipping price was fairly reasonable and only an extra 4$ for express fedex shipping. Diff bushings won't be getting installed just yet, will do them when I do a LSD conversion a little bit later on, saves dropping the diff twice.

 

Cheers