Dom's 69 BB car has been driving him crazy with power steering problems. It worked fine when first put together then it stared loosing the power at low speed (sometimes) then it got to the point it wasn't driveable. He changed the pump (twice) and put in a rebuilt box. It would sort of work a low speed if you set the idle over 1000rpm then it quit. Any ideas? Did he manage to get bad rebuilds? (they aren't Autozones etc)

If it's a low speed problem then he needs more pressure. Rebuilt pumps usually require you to swap in your old pressure relief valve. There is an inlet screen on the nut end of the valve, make sure it's clean, then remove the nut and remove a shim to raise pressure.

Wide offset wheels aggrivate the problem, also if you have your foot on the brake when turning the wheel.

Belt slip is another problem you can run into. Make sure the belt is clean, since oil can easily be spilled on the belt when filling the pump.
David

I think he has already tried that. The problem is that it comes and goes for a while before it quits. I had it happen to me when I was trying to turn into his driveway the power steering just quit. It had been fine up to that point. I am beginning to think something is wrong with the relief valve that is causing the mess.

What fluid is he using?

He was talked into using so called power steering fluid.

Although I always recommend that you use genuine GM power steering fluid for maximum durability, I doubt that some other brand of power steering fluid would be causing the problems as described.

When you say that you lose power steering, does it happen after many miles of successful driving? Or does it occur immediately after replacing a pump? Do you always deairate the system after working on any of the fluid carrying components? The reason I ask is because when you change a major steering component it is possible to have air in the system that can cause a lack of power assist for a couple days (but it will finally cure itself).

When you have to raise the engine rpms in order to get some power assist, it is a lack of flow from the pump that is the problem, not a lack of pressure. If you can steer lock to lock with the car stopped and your brakes applied, you have sufficient pressure. Lack of flow can be caused by a slipping belt; by a pump that has internal problems; the wrong size pump pulley (too big in diameter); or possibly low fluid level.

It is possible that crud in the steering fluid could cause the flow control valve inside the pump to stick. This is the slider valve right behind the discharge fitting that the power steering hose screws into. Possibly flushing clean power steering fluid through the system might remove the crud and particles. Disconnect the low pressure return hose from the pump and aim it into a bucket. Plug the spout on the pump reservoir. Have someone add power steering fluid to the pump reservoir as you steer lock to lock.
http://i2.photobucket.com/albums/y38/JIML82/P-PumpFlowCntrlValve.jpg
Remove the discharge fitting and use a probe to press on the valve. Make sure that it will smoothly slide back and forth inside the pump against the spring. As shown on the diagram, the spring is the first thing that goes into the pump cavity; then the flow control valve with the hex nut and screen first (pointing toward the driveshaft end of the pump); then the discharge fitting.

On a 1969 vehicle you should have a pump that has the pulley retained on the pump shaft by a nut and a square key. You shouldn't have to hammer or bang on the pump shaft in order to assemble or remove the pulley. Hammering on the pump shaft can damage internal pump components.

These are just some thoughts.
JIML82