Are Current OE Rear Subframe Bushings Improved?

[Slideways]

For anyone who has installed solid subframe bushings, are the two front bushings supposed to contact the hex on the subframe mounting stud or the RACP sheet metal?

CMP changed the design slightly to match other solid bushings which seem to contact just the hex portion of the subframe stud. The previous CMP bushings had a machined portion where the hex slotted in:




Edit: CMP replied saying that both older and newer style bushings only contact the hex portion on the front subframe studs. The redesign helped with manufacturing costs and made the bushings 15% lighter in weight.

[HighOnLSB]

Another street car on solid subframe and monoball RTABs. No increase NVH while driving or in regards to M-clunk.

[old///MFanatic]

There is no nvh when switching to subframe solids IF, all your other bushings from moving components that attach to the subframe are stock rubber.
I would add that, because solids increase localized stresses, it is recommended that solids are put in cars with additional reinforcements (topside kits for front and rear mounts, not just underside plates).

My main concern is removing the firmer ///M mount design that is still designed to absorbs the impact stress. That is main concern.

Also NVH evaluation is usually associated with car rolling (idling). Most have forgotten and just use to the M clunk. Curious, are you able to comment that with solid that has not increased in chassis going from rubber M mounts to solid? One might expect that increase over stock M rubber mounts. Sure it’s a non-issue for track car, but would think street car one might not want that increase. Interesting to get some feedback on that from those with. Much appreciated.

[old///MFanatic]

UHMW (what Condor Speed Shop has been making) is a stone's throw away from solid, I don't understand the hesitation in just getting solid mounts? All M cars starting with the E92 GTR and F8X cars have the rear subframe solidly mounted, and most people I've seen post their experiences switching to solid mounts say there's no NVH.

Yeah thanks for input, much appreciated. I get these are just a one step from complete solid. I mentioned it as he’s also in the solid (semi) mount camp, as you all are.
My overall hesitation is the “impact stress” solid produced to the mounting area. I do not want to have to install a full top mount bracing to alleviate the damage often seen after solid mounts.

E92 GTR and ///M F8x chassis cars have very different subframes footprints. It was designed that way. It’s what in business we’d call two different animal designs. Saying went something like “Don’t expect wings of an eagle put on a swallow to work better because they do on the eagle”.

[LSBNick]

Been on solid subframe bushing with monoball SDW RTABs and oe diff bushings. No added NVH at all and the car feels super solid.

[S14]

I have a street driven car and went with bimmerworld solid bushings and OEM type of joints of bushings everywhere else. I've had plenty of cars that I went full race-car-but-still-drive-on-the-street which is always a horrible choice at the end. The solid bushings are not noticeable at all in greater NVH.

[oceansize]

There is no nvh when switching to subframe solids IF, all your other bushings from moving components (front and rear diff mounts, inner upper and inner lower control arm bushings) that attach to the subframe are stock rubber (they isolate the nvh).

I would add that, because solids increase localized stresses, it is recommended that solids are put in cars with additional reinforcements (topside kits for front and rear mounts, not just underside plates).

I just swapped to solid CMP subframe bushings (had AKG), and also swapped to stock front diff mount (also had AKG), nvh is now a lot lower than before.

Sent from my SM-G950U using Tapatalk

That first sentence is the truth but I don't think old///MFanatic trusts us much Can't say I blame since we are a bunch of rapscallions.

I will say this about myself. I don't recommend things because I bought them and I don't recommend things because I know people in the industry (I don't). If something sucks it immediately gets ripped off my car and thrown directly in the trash. When I pulled out my powerflex polys I threw them in the trash with only 2k miles on them because I didn't want anybody else riding around on that garbage. Engineering wise I won't argue with professionals but on the e46 BMW blew the RACP design so badly that I really wonder how such a thing occurs. Completely unprofessional and I place no confidence in anything to do with our RACP in their hands.

[mrgizmo04]

There is no nvh when switching to subframe solids IF, all your other bushings from moving components (front and rear diff mounts, inner upper and inner lower control arm bushings) that attach to the subframe are stock rubber (they isolate the nvh).

I would add that, because solids increase localized stresses, it is recommended that solids are put in cars with additional reinforcements (topside kits for front and rear mounts, not just underside plates).

I just swapped to solid CMP subframe bushings (had AKG), and also swapped to stock front diff mount (also had AKG), nvh is now a lot lower than before.

Sent from my SM-G950U using Tapatalk

[r4dr]

UHMW (what Condor Speed Shop has been making) is a stone's throw away from solid, I don't understand the hesitation in just getting solid mounts? All M cars starting with the E92 GTR and F8X cars have the rear subframe solidly mounted, and most people I've seen post their experiences switching to solid mounts say there's no NVH.

[old///MFanatic]

My tech buddy been suggesting I go with UHMW Polyethylene. It appears to be delrin-like material. He says they like the results, not the cons of polyUrethane. Says NVH levels are minimal too. Although I’m sure impacts are not isolated well, but nicer than solid.

[old///MFanatic]

Yeah actually we use to do this job at my friends old shop. Back then it was the 328s/323s that had biggest issues. TMS was pretty much the go to plates and Powerflex bushes. We’d see some of the PF bushes later and they’d oval. In fact a lot of poly bushes we’d see oval out, deform and need lubrication to keep squeaks down. Really no engineering at all to things that original parts incorporated. Front diff mount another example, that part is fairly complex, polyurethane ones just a void filler.
BMW has a lot of engineering dealing with vibration/harmonics. It’s hard to believe looking at design that they’d just make the top/bottom ridges a particular intricate costly way than just a larger area if it wasn’t better. Granted I’ve certainly seen parts improved upon, with trade offs ranging from minimal to large.

I’m hoping to gather most current info from others like you to help make decision. Sometimes ///M parts for street are the best selection, sometimes they’re not.

[mrgizmo04]

Just as fyi, those green tabs you see in the pic in the first post don't actually provide a "larger area" or "more stability" for the bushing. Especially in the front, where there is a large hex that the bushing inner sleeve (the silver metal part of the bushing) rests upon when everything is bolted up. That is why it is so important to do longer through bolts and cups in the front, because most of the forces are around the front studs. Also, most of the load of racp is on the 2 front mounts (see how the upper and lower control arm inner attachment points are super close to the front), so the 2 rear bushings act more as stabilizers in the compression/extension direction, but most of the critical articulation is around the 2 front mounts.

Sent from my SM-G950U using Tapatalk

[oceansize]

Thanks for your response. If you could please elaborate what “fresh” is? I’m sure everyone could envision differently. Age/mileage/environment/use all considerations.
Also really hoping to hear about the new revised ones. By chance were these the newest revised Genuine BMW M3/Z4M ones or previous ones.
Thanks for your time.

Sorry for the wording, brand new OE. Unfortunately I didn't put those in as this was done by the shop doing my reinforcement in October of 2017. I ran those for around two years then I put in the poly and then just a few weeks later the solids (CMP). I didn't like the polys (noisy and felt off, can't really put into words) but it seems most guys who like poly have used the AKG stuff. I don't really have any complaints about the OE bushings.

As an aside here is Vince from Vince Bar fame referencing his personal choice for subframe bushings along with his reasoning (timestamped):

https://youtu.be/Ktbo3SdmRPg?t=719

[old///MFanatic]

I went from fresh OE to Poly to Solid (within 7000 miles). I won't be going back to either OE or Poly. Assuming you are reinforced then the only concern would be the NVH which is of no consequence.

Thanks for your response. If you could please elaborate what “fresh” is? I’m sure everyone could envision differently. Age/mileage/environment/use all considerations.
Also really hoping to hear about the new revised ones. By chance were these the newest revised Genuine BMW M3/Z4M ones or previous ones.
Thanks for your time.

[Tbonem3]

If you're doing top side reinforcement, I don't see any issue with using stock bushings. If BMW had simply reinforced the mounting points from the factory, we wouldn't even be talking about any of this. Race cars would still go solid sure.