Vibration in the engine
 

I have an 1972 Mustang Grandé with an 302cu engine which virbrates like hell. Everyone I asked before, told me to replace the vibration damper, which I did. After that, the vibration got less, but is still there. How can I be certain what the problem is, could it be tuning ignition or something like that?? The damper costed 300 euro (I'm from Holland) and before I'm gonna spend that kind of money again, I want to be certain what the problem is. Please help me, I'm desperate.

can you give more details about the vibration? does it always occur or only when you idle? when did the vibration start to begin? did it happen all at once or started small and got worse. have you changed anything recently?