vibration 390 C6

Any ideas on how to troubleshoot a bad vibration on a 66 T Bird with a 390 and a C6 tranny? The balancer does not wobble. The vibration is at a set rpm moving or sitting still. Any wat to isolate vibration without pulling tranny?
[addsig]

even for a wild guess even the best mechanic would need more information. A little history on the car and the problem would go a long way.

Did this just start? Is this a car you bought and it was already this way? Or have you owned it for a while and the vibration developed over time.

Any strange noises. Have you had anyone local take a look at it?

I just purchased car and the owner says he has no knowlege of problem. I am trying now to get it to a local shop but they are booked for the next few weeks. No strange noise but maybe a faint rear end noise,
Thanks
[addsig]

If the car has not been modified...based on the information from the previous owner (for what that is worth). That tends to remove the idea of an imbalance in the flexplate, the 390 engine and the 428 flexplates look very much alike. One is neutral balance the other has an weight, if some one replaced it with the wrong one...you could have that vibration, most noticable at certain rpms, when the harmonics converge.

From what you have discovered; I would probably suspect motor mount, transmission mount or universal joints. Unfortunately for a Thunderbird, since every thing is tied to everything else, it'll probably be a piece of work to get to anything in the engine compartment...even just to take a look. If the motor mounts haven't been replaced, are seriously bad...you might be able to see the engine move around a lot. Then again, you need a point of reference to know what is "alot". That brings us back to having "eye-balls" on the problem.

tese are just places to start looking...obviously a shot in the dark. ?

<font size=-1>[ This Message was edited by: Beoweolf on 2/19/06 11:44pm ]</font>

Thanks
Transmission mount ordered
looking for motor mounts
[addsig]