Vibration Question

ricks70dart said

Asking for a friend,He has installed a rebuilt 727 and rebuilt torque converter behind his 340 which is in a 69 Dart.He has a vibration when revving in park and when driving on freeway speeds. Could this problem be the rebuilt torque converter not balance correctly. Any input would be greatly appreciated Thank you Rick

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Absolutely.
There are three things that can have an effect on balance.
Engine rotating assy, converter and flex plate. (and harmonic balancer in the front) but we'll skip that assuming for now it is the right one.
If the engine (rotating assy) requires external balancing, it needs a balanced converter or a balanced flex plate.
Either one could have the balance weights.

He could have balance weights on both as well, which would also cause a vibration like you describe.

340's are internally balanced so if the converter and trans were from a 360 or 318 there's the problem.