Violent shake
 

I recently purchased an 80 vette. The previous owner had replaced the power steering control valve and I suspect they didn't adjust the balance. I had the car up on jack stands and started the car to observe how the wheel turned to the right. As I turned it back to left the car shook violently. Once I adjusted the balance the vibration is still there at certain points as I turned the wheel back and forth. However the vibration was mild compared to before. Could the power steering control valve be the cause of this vibration?

Did the PO say anything about the vibration? Can you still contact the PO?

the guy I purchased the vette from was acting as a broker for the owner. Only history he had is what the owner wanted him to have.