So I put new poly urethane motor and tranny mounts. I know its stronger than rubber so a little vibration will be noticed but this is NOT normal. I mean I cant even accelerate semi-hard without the whole car shaking?? I feel it slightly around 15 mph but really noticed it when I go to about 40 mph....I dint go any faster than that cuz it scared me. What could this be?? The car ran great before I did this....no other changes we made, no modifying/cuts or anything.....I'm lost

 

Only thing I could think of would be forgetting to bolt one mount in. Otherwise, sounds like poly mounts

 

ive got solids in my 5.0 the vibrations arent that bad ill bet youhave a bad u joint or something along those lines and u didnt notice with the old flimsy mounts not that everything is all tight its significant

 

How do you know when a u-joint is bad?? I had the driveline cut and balanced and a new u-joint put on it....but that was a few months ago, and it was on the old mounts. The reason that I replaced the mounts wasnt just simply for an upgrade, it's cuz the old ones were completely shot!!! I mean tranny mount....in several pieces, driver side motor mount in 2 pieces...and the passenger motor cracked, but still in 1 piece. So could replacing these mounts somehow of affected the u-joints??

 

Did changing the mount significantly affect the drive shaft angle? If you have too much of an angle it will cause a vibration that happens with speed...I would look into that first.

 

I'd go back & check that the universal at the differential was centered properly before the bolts were tightened.
Have you been able to determine if the vibrationis RPM related, would indicate engine. Or road speed related, prolly universal.
Take it up to 40, if you feel safe, check vibration related to RPM as the gears change. At 40 go to neutral & let the engine go to idle. If the vibration stays related to road speed, it's probably not the mounts.

 

It could be an engine balance issue that you didn't notice till you had motor mounts that didn't suck. Check your drivetrain first like everyone suggested, u joints, pinion angle, tire balance etc

 

If indeed it is the angle of the drive shaft, how can I change it to make it work?? Can I still use the tranny mount that I have?? It was a kit from summit reccomended for my car.....so I dunno why its not working??

 

Is you car particularly low or high ot the back? this will also effect you driveshaft angle. Im guessing that the rear is really sagging, and then with the new mounts, its lifted the engine to the correct angle, but the drivshaft is angled up to meet the diff.

 

SO.....if the angle of the drive shaft is my problem....how do I fix that??