1974 F100 2wd 302ci Automatic PS PB everything under the hood basically stock.

Ok, so I bought this truck last summer, the PS was working fine functionally with strong power assist - but - the pump was growling/grinding very bad - very loud. I flushed and bled the PS to no avail - made no difference. PS still operated strong but very loud growling - gear like sound - not like air in system like sound.

This is the round steel can type PS pump.

Being concerned it would go out, I replaced the PS pump with a new Lares 12038 - I went with new due to hearing remans of this pump can be hit and miss...
Anyway, I've replaced my share of PS pumps on 1980's and newer vehicles and have always been able to bleed the system, no problem, but this new pump on this truck refuses to bleed, at least via the procedures I'm using.

I first flushed the system before disassembling - so that the new components would have fresh new fluid right off after their installation.
I then replaced the pump, the supply and return lines, and added a PS cooler and inline filter.

After installing everything initially I added fluid, then with engine off and front wheels off the ground, turned the wheels lock to lock about 50 times while periodically checking/ topping fluid as needed.

Then I used my power steering vacuum pump setup - and with 10 inches applied (PS holds vacuum, no leak) - I again did the engine off, steering wheel lock to lock, again periodically checking/topping off fluid as needed, about 50 times. All seemed well, got all air bubbles out of the fluid.

I then (still wheels off the ground) started the motor and slowly turned the wheels lock to lock about 10 times. I heard whining like air is in the system. Turned engine off, and foamy fluid erupts from the tiny fill tube - like a volcano - sending fluid to the valve covers, etc.

I have repeated the above bleed procedures repeatedly and every time - before I start the motor - after much bleeding I get all air bubbles out of the fluid - then start the motor and it's as if the pump is rapidly churning huge amounts of air into the fluid - and the volcano of foamy fluid erupting as soon as the motor is turned off.

Has anyone seen this? Maybe I got a bad new pump? Are Lares pumps to be avoided?

I did put the wheels on the ground so I could let the PS pump feel the load of turning the wheels - and look for leaks under pressure.

There are no leaks under pressure, no leaks under vacuum, and fluid is flowing - albeit foamy if the motor is started.

Every time I (extensively) bleed I get the air out of the fluid, then when I start the motor even just for 10 seconds it's back to foam for PS fluid - not just air bubbles - but erupting foam.

I've never seen anything like this and am baffled.

I got the PS Pump from rockauto and I'm past their 60 day return window so can't return it. Will have to buy yet another pump if that's the problem.

Before buying another PS pump, thought I'd see if I should try something else. It seems to me the PS pump is causing this, but maybe it's something I'm doing wrong???

Maybe I should just switch to the Saganaw setup? I'd prefer to use the existing PS system if possible.

Thoughts?

Thx!

BTW - I do still have the old PS pump...