Power steering pump overflows

[trevarthan]

My 71 c10 4.1L six 2wd has developed a power steering issue recently.

The guy I bought it from, years ago, said the truck had manual steering from the factory, but he replaced it with power steering components from a similar model (perhaps the V8).

Anyway, power steering fluid is overflowing from the power steering pump cap after the engine is shut off.

I replaced the high pressure supply and low pressure return lines, thinking it was a leak. The return line rubber hose was slightly cracked, so I thought this might be the issue.

Unfortunately, the issue is still happening.

I've been bleeding the system for about 4 hours now, moving the steering wheel lock to lock with the engine off and watching for bubbles.

There must still be a leak because I'm still seeing bubbles after 4 hours and it's continuing to do the same thing if I turn the engine on. Plus the pump sounds terrible with the engine on.

How do I diagnose this? I want to identify the source of the leak without blindly replacing more components. I could replace the pump, but what if it's the gear motor? etc.

Thanks for any help. I'm a little bit at a loss here.