I have a 1970 Boss 302 with manual steering. It steered OK and returned to center after turning a corner.
I then purchased a complete rebuilt OEM power steering system: pump, pulleys, brackets, hoses, control valve, boost cylinder, center link, etc. Everything installed nicely, no leaks and the power assist works good. The only problem I'm having is the steering does not return to center on its own after turning a corner.
After I installed the system I had the steering aligned by a shop that specializes in old muscle cars so they had the right setup and specifications for the correct alignment. But, still no return to center. I took it back and had them add more caster to see if that would help but it didn't.
When I installed the system I also replaced the passenger side idler with one from NPD that is supposed to be for power steering since it is the rubber bushing in this idler that is supposed to help the steering return to center.
If you put the car in the air with the engine off, you can grab a wheel and turn it lock to lock with just the normal resistance, so nothing seeks to be binding up. The boost is equal whether turning left or right, car steers and handles great on the road.
Any ideas on what could be wrong?