Vibra-Technics Rear Motor Mount and why polyurethane bushings might be a bad decision

[Adub]

I just ran into this 2 weeks ago. The bracket's hole doesnt fit the vibra technics stud until it gets pressed into place either in a vice before hand OR while tightening into place it should press fit into the correct position. I havent gone back to revisit it yet though. That info was given by the forum and it should be found in the install instructions.

Did you have a mountune one before this one or a counter sunk one?

 

[gtx3076]

To clarify you had to drill out (make a bigger hole) the existing counter-sunk hole that you had used for the mountune RMM to fit the vibratechnics?

No. The hole in the stock bracket is not counter sunk, it was actually hex or octagonal. I posted a photo of it months ago. I don’t know anything about mountunes RMM.

 

[Adub]

And again after the rebuild. These bushings had less then 10,000 Mi/16093 Km on them when they started to fail.

Maybe you can help since you had a mountune RMM. Did you have to get a new OEM RMM bracket to install the Vibratechnics mount since the original one had the be counter sunk / drilled to fit your previous mountune one?

 

[TyphoonFiST]

I just placed my bracket on the Vibratechnics RMM and gave it a couple taps with a Rubber mallet.

 

[akiraproject24]

Did you have a mountune one before this one or a counter sunk one?

No I have the whoosh

 

[Dialcaliper]

I had Powerflex inserts for the two upper mounts and a series of different poly mounts, and was noticing a thunk starting to develop again under load.
Replaced all three with a set of Vibra-Technics, and have been mostly ok with it so far. Certainly more NVH than stock, maybe slightly reduced from before, but the thunk is gone.
The poly in the upper mounts was starting to harden, allowing the thunk to develop. The RMM was torn (again- I think this was number 3?). I'm hoping that these will last longer and not get horribly buzzy at cold temps. I think the failure mode is that the heat from the cat weakens the poly in the RMM, and this eventually degrades, allowing more flex and wear on the other mounts.
I think that there is tendency for folks to install a RMM, and this causes increased wear on the other mounts- but I am no engineer.

The problem is mainly that cast polyurethane is simply not a material that holds up well to heat long term compared to automotive rubber that’s direct bonded to metal inserts. The stiffer mount and NVH isn’t really the issue (if anything, stiffer mounts absorb less energy).

Polyurethane is used because it’s easy to cold cast in small batches with a variety of durometers and color choices. Cast rubber is more complicated and requires a heated process, and the tooling cost is usually not economical except in large batches, especially when metal-rubber bonding is involved.

Any polyurethane mount in the RMM location inches away from the catalytic converter is going to degrade and need frequent replacement. A metal-rubber bushing that lasts longer is going to cost more to produce - that’s just how it shakes out.

My car already had the whoosh when I purchased it, and when I noticed it going, I opted to get the replacement kit whoosh sells as it’s a cheap option. When I emailed Ron about it, he was straight up honest that based on the feedback he’s gotten, the Poly RMM bushings are basically a consumable, and the stiffer “race” bushings last slightly longer, which is why he started offering a replacement service kit at the best price he could.

Knowing what I know now, I may consider the rubber RMM in the future.

 

[its_stock]

Maybe you can help since you had a mountune RMM. Did you have to get a new OEM RMM bracket to install the Vibratechnics mount since the original one had the be counter sunk / drilled to fit your previous mountune one?

Sorry I'm late to the party, I just installed the bracket as is. It was a little tight but went together with no dramas.