Harmonic Dampener: bad?

Can Harmonic Dampeners go bad? I keep getting an engine vibration at high revs. The LT-1 motor is new (rebuilt), and so are the engine mounts, but the dampener is the original 10-year old one. Not sure how they work. I have heard of Fluid-dampers....

what type of crank did they use on the rebuild?. I have heard of this happening on many rebuilds and this usually cures it " HUB AND BALANCER
The balancer is a two-piece assembly with a pulley that bolts onto the hub. Separating the two made it easier to install the Optispark distributor on the assembly line and out in the field. The holes in the hub are offset, so the balancer only fits on it one way, but there’s no keyway in the hub to index the hub on the crank. This shouldn’t be a problem unless the damper was drilled at the factory to "trim" the final engine assembly.
If it was drilled a lot to compensate for an engine that was out of balance, you could end up with a shaker, depending on how everything stacked up with the remanufactured engine compared to the original engine. If you encounter a balance problem on a remanufactured LT1, try rotating the balancer assembly on the crank 90° at a time to see if it eliminates the problem." taken from http://www.automotiverebuilder.com/ar/ar99928.htm

Thanks for the info. Makes sense.

No problem, good luck and let us know how it turns out.

John