honda1
Hello & Welcome to the Forum...
l had a locomotive that had a similar problem.
The gears were worn and didnt mesh, so it locked up.
l had oned l accidently put back together out of quarter, and that locked it up.
Your Lackawana, which one is it? they produced a variety of them. 
 My favorite was the Camelback.
This is where pictures would help identify your loco & its' problem.
My guess is to make sure your gears lineup & everything well lubricated.

Happy Rails...
dave