Technical power windows

I am working on a 1964 Impala SS with power windows. I tested the old motors off the regulators and they worked fine in both directions, but slow. Back on the regulators they only work one way. They would start the other way but quit. So I bought new motors and have the same problem. On one regulator I loosened the motor and it worked fine. So why is it binding up? No slop or stiffness in regulators, they move freely.

 

Maybe bent just enough? Maybe some lubrication could help? Had a Toyota where the motor was bad and the regulator felt fine but needed a little lubrication.

 

When you say the regulator works fine is that with the window hooked to it and in its tracks?

 

No, that's on the bench working it by hand, it works freely. Same with motor attached, on the bench. Works one way, but not the other.

 

Thanks