gbmarc

This one has me a bit stumped. I just replaced the pump to rack hose. (Actually, because of the price of a new one, I had Spokane House of Hose rebuild mine for me. Although I don't think that's significant.)
I started the car, drove out of the driveway and everything was fine. I reach the top of my road and whoaa! No power steering. And I mean, stiff like as if you had tried to turn the wheel with the engine off. Then as soon as I accelerate to 2000rpm it kicks back in. When I came to the shop's parking lot, I could barely turn into the space. In fact at slow speed, the only way I could manipulate the car is by putting it into neutral, revving the engine and then turning the wheel. As long as I kept the revs up I had power steering. So what's going on? Here's what I did:
I went home, raised the front of the car and bled out the air by turning lock to lock and added P/S fluid because it was low.
I went for a test drive but there was no improvement.
Then I pulled at the Servotronic relay to see if the servotronic valve thingy had the correct resistance. It was OK at 8 Ohms between terminals 2 and 5.
Then I pulled the P/S rack return hose and started the car to see how much fluid was pumping out. It pumped very fast at idle and I had to switch off quickly before my container overflowed.
I have a new serpentine belt and new belt tensioner. Why should I suddenly have problems after installing a new hose?
One other observation - when I first start the car after a rest the power steering initially works even at idle, but at the first or second slow down to turn, the P/S totally disappears.
Is it possible the constrictor in the return hose has become blocked? Because when I did my disconnect-volume-pumped test, the constrictor wouldn't have been a factor. As the constrictor sits in the hose (from cooling loop in front of the radiator) about 5" from the return inlet to the reservoir.

gbmarc

I think I have a theory on what's happening:
The pump I believe has a pressure relief valve built in. As the pump spins faster and builds up pressure it pushes back the valve against a spring and opens up a passage to bleed off pressure, hence preventing a dangerous over pressurizing of the system.
I believe my valve is temporarily sticking open. This is fine as long as the engine revs are higher but when coming back down to idle speed, there's not enuf pressure.
If I leave the car for an hour and come back the valve has slowly worked itself back and returned to the closed position, meaning I get full assist at idle speed.
If this is correct, then if I drive the car at idle and never rev to push the valve back it would never get stuck. I tried this out and indeed I wandered around the neighborhood like a funeral hearse and never lost power steering once. As soon as I accelerated to 1500 rpm and then back to idle, I lost steering assist.
Now the question is whether I can remove the pump and free up the valve or whether I could shoot some lubricant into the pump in situ to free up the pressure valve.

gbmarc

Here's the conclusion to this story:
I took the P/S pump off. (It's not too hard but the electric fan has to come out to give access. Also the pulley has to come off in order to get at the 3 mounting bolts.)
Once out, the pump then splits easily into two parts by removing 4 bolts. The pressure relief valve can then just be pulled out of the center cylindrical hole of one half, or at least it should if it's not stuck. Mine took some wiggling. On examination I could see a scratch mark where obviously some dirt had damaged it and so it no longer slid back and forward smoothly. I cleaned it up and polished the valve cylinder and the bore it slides in until it slid easily in and out.
I then reassembled, refilled with fluid and bled the air out by turning the steering lock to lock (with the wheels off the ground)
The problem was then fixed and assist returned to normal.