So I upgraded to poly-urethane... Hope this stuff will hold up... If it goes bad what do you think could be causing this to happen?

I was thinking motor mounts if they are bad the engine might be putting pressure when its vibrating or rocking, or is that too absurd?

 

I'm curious about this too because my motor mounts are starting to go, not too bad but i can feel (and see) the engine rockig around a little.

 

I would replace the motor mounts and have the driveshaft checked for true balance.

 

Well, the urethane trans mount isn't going to separate. The stock rubber mounts are just bonded together, the urethane ones have an interlock bonded into the urethane.
But I'm curious too as to why you ate up the other two? Are you beating the crap out of the car? Automatic or manual trans?

 

its an automatic with a moderate shift kit... I dont beat up on it too much especially lately since the passenger side header gasket is messed up.. thats another thing I go through header gaskets left and right... and I was thinking if its bad motor mounts its causing the engine to vibrate too much and making the headers move a lot causing seperation between the pipes and the block... who knows if my logic makes sense

 

a torque arm relocation set up might help. something like this.
http://www.stranoparts.com/partdetai...=107&ModelID=2

 

sweet ill take a look into it

 

This sounds like motor mounts to me... did you mean to say that you have polyurethane motor mounts?

 

No I dont... I replaced the tranny mount with a polyurethane one and I have a question is it normal to feel a lot of vibrations and shakiness while driving? I know its like a solid piece and it doesnt absorb vibration like the standard mounts...

 

u will feel more then normal but nothing to worry about, like BandidoLenny said have the driveshaft checked for true balance