[pggto]

I have a 70 GTO convertible that has had a vibration in it years! In that time frame I have replaced everything that moves. I have changed rear ends, engines, trans, drive shafts, brake rotors and drums, wheels and tires, and suspension bushings and related parts. The vibration is still there, it's like a pulsating harmonic type vibration that resonates through the car that kicks in at about 2600-2800 rpm and gets worse with more revs and mph. Now that I put a more powerful engine in it this summer it's worse. It was just annoying with the other engine, now it just pisses me off with the new engine. I had everything balanced with the new engine. It vibrates so bad you can't see anything in the rear view mirror! Could the pinion angle be causing this????? What should the angle be? How do you actually measure the angle? I was going to install adjustable rear upper control arms, but I'm not sure where to start. I've noticed this vibration in other A body convertibles but not as bad as my car. Any input is welcome, thanks.