Kwish

So, a couple months ago I had my 12' E550 AWD in to get polyurethane engine mounts installed along with a TCU tune and some other goodies. I cannot remember the brand of Polyurethane mounts that were used, I'm just wondering if anyone else has poly engine mounts and has some new noises when they were installed? Like some clunking when tapping the throttle, minor buzzing when cruising etc. I've had my vehicle inspected multiple times and it seems like this just might be a normal thing with stiffer polyurethane mounts now?

S. Madman

Never hand them on this car, but had them on my Mazdaspeed 6 some years ago. Polyurethane mounts need to be retorqued after they settle. I am surprised you did not feel the vibes the moment you put them on though.

Kwish

Well, I definitely notice a little more vibrations. But I expected that. What was a little more concerning was some noises that have shown up but no one can find anything loose or find a potentially an issue. But, I'll probably end up just driving it until the noise gets really bad or something fails. At this point it seems to be shifting fine, running good and the steering is still tight.

AllPhonesAretap

Does the buzzing occur throughout any RPM or only withing a certain range?

Kwish

The buzzing actually seems to be speed related, itll buzz starting around 35-40 and also will get louder when decelerating from like 50mph+

S-Prihadi

I hope it is not the faulty "design" of the poly mount.
Engine mounts are not as simple as one think. Harder is not always better.
Its success is the reduction of vibration and resonance transmission from engine to chassis and drive train.
Its hardness (duro) and yada yada are engineered calculation.

Some real good ones as in MB original ones are short lived ( for me 25K KM max ), but its worth the investment as far as super smooth operation.

If you want to "tighten up" your car for faster power transfer to drive system, suspension is more the department that can help.

CaliBenzDriver

This sounds like Xfer case or rear diff. whistling.
When did you service these oils..? Magnetic plug?

The rubber shaft/mounts couplings help soften vibrations from propagating through.

Once place seen as super beneficial for poly stiffness are control arm bushings. The soft factory bushings are primarily built for comfort with relief slots... these are my type ✌️
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Kwish

If not mistaken, the transfer case fluid is shared with the transmission is it not? I had that serviced along with trans filter maybe 10k miles ago? The rear differential will be getting done soon, I didnt have time to do the work myself but the shop I had do it never said anything bad about the fluid coming out or anything out of the ordinary on the magnetic drain plug. I do still have the factory control arm bushings as well, I only had the engine mounts replaced with poly for longevity purposes and to help with the amount of power I am putting down now.

CaliBenzDriver

I know very little about the 4Matic setup and scheduled maintenance to prevent blowing up its bearings and shafts when neglected.