I have an '89 vert and the vibration starts @ 65mph, and gets really bad @ 70mph. The vibrations comes straight up through the shifter.

I thought it was the tires, so I had them balanced...didn't work. So then i went and bought new ones b/c they only had a few thousand miles left on them anyway. It's a low mileage car (49k) and my 16" ford rims have about 2k miles on them...the previous owner put them on and i've had the issue since I purchased the car.

Any recommendation for what the problem may be and/or how I can diagnose it?

 

So your car vibrates or your shifter vibrates?

 

the whole car vibrates, but it's more pronounced through the shifter....

 

Maybe you have a bent axle, have a friend follow you with another car and ask him to check all wheels and see if any of them wobble. I bent my axle once and drove around not knowing it until someone told me my wheel was wobbling. I never got on the freeway so my car didnt shake noticeably.

 

Balancing tires does not neccessarily rule them out. Could be out of round, have a flat spot or a hard/soft spot in the sidewall. Most of the time you can see those problems if you jack the car up and rotate the wheel and watch for runout.

Another distinct possibility is the drivehshaft.

 

Right now it has brand new tires, so I believe the rubber is ruled out.

I'm thinking possible drive shaft or trans mounts...any idea the proper procedure to test this theory out?