transmission support

[70challengersix]

Does anyone have any experience with mixing rubber engine mounts with a polyurethane transmission mount?

I am getting a vibration off idle that I cant find the source for.

[Moparal]

If your new trans mount is installed higher or lower than the original height. You may be experiencing the wrong pinion angle

[70challengersix]

Vibration drops put when shifting into nuetral,  so I believe that eliminates the pinion angle. 

[Moparal]

Vibration drops put when shifting into nuetral,  so I believe that eliminates the pinion angle.

not necessarily.  Depending on neg or positive angle  accellerate/decellerate...  been there

[70challengersix]

Just to document this hard to find problem, the vibration noise I was getting, most prominent at 35-40 mph was, a hmmmmmmmmm space hmmmmmmm space hmmmmmmm. Very consistent and annyoing throughout the car.  I could also pick up a little vibration throught the steering wheel and seats.  It sounded like tires/drivetrain, but I couldnt find anything wrong.

This was driving me crazy and the noise vibration was at the point where I didnt want to drive the car, however now, Problem solved, it was indeed the polyurethane transmission mount.  Althought the manufacturer advised this could not happen, after swapping their new $50.00 poly tranny mount and  going back to the $10.00 stock rubber mount (that matched the rubber engine mounts), the car runs smooth with absolutely no vibration whatsoever. I would not recommend mixing the material types poly/rubber between the engine and tranny mounts.  I don't know if poly mounts are availale for the engine and if they would have interacted differently with the poly tranny mount, however in the future, I will stay with all rubber.

[Chryco Psycho]

so here is the question , was the poly mount transmitting a vibration that still exists ? The problem may still need attention although you cannot feel it now .

[70challengersix]

so here is the question , was the poly mount transmitting a vibration that still exists ? The problem may still need attention although you cannot feel it now .

Thats an interesting question, however, how would one know that without mounting accelerometers on the engine and transmission upstream and downstream of the mounts. I have not detected any significant abnormal "visual" vibrations of the engine at idle or during rev, either before or after this tranny mount change.  I also had the car on a lift watching the mount with the car running and cannot detect any significant motion (although I have to say, I didnt look at this connection in the same way with the poly installed).   I think this poly material is a little stiffer/less forgiving in comparison with the rubber. 

[MEK-Dangerfield]

I think this poly material is a little stiffer/less forgiving in comparison with the rubber.

 Most definitely.     It's the same deal with the suspension. Poly is stiffer, and not as forgiving.

[73restomod]

Had a similar problem once before, you'll get an oscillation type vibration at certain road speeds?

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