Sudden Power Steering Problem

[saxart]

I'm having a problem with the power steering on my '70 C-10. Hoping someone has some thoughts.

The truck was recently put into service after getting a new crate engine, rebuilt power steering pump, and red-head steering box. I purged the box exactly like Red Head's website instructs. (Jack up front of truck and work steering back and forth 15 times with engine off, do it again with engine running, all while topping up the pump with fluid when needed.)

The air-purge went fine, and at the start of the maiden voyage the steering was really nice. Smooth, easy turning and linear across it's travel. About 2 miles into the trip, the steering got VERY stiff. I pulled to the side of the road to check the power steering fluid level, expecting it to be low, but it was not, so I nursed the truck home to investigate.

After getting the truck back up on jack stands and working the steering back and fourth, it's still VERY hard to turn the wheel, and the steering box pukes fluid out of the top of the reservoir. I thought maybe there was still air in the system, so we kept working the steering box back and fourth about 30 times with no improvement.

What happened here? Could the Red Head steering box be bad?