Power Steering



That is the bleed screw for the PAS system. It works very much like the bleed on the brakes, in so much that it lets the air trapped in a closed system out with out letting more air in.

To bleed the system, not a bad thing to do every six months or so, start by cracking loose the bleed screw, use only a box wrench or socket, an open end may strip the flats. Then close the screw and start the motor. Turn the steering wheel from lock to lock, then center it, then with the motor still running, crack the bleed screw a little and leave it open until the fluid is running out and has no air.Catch the fluid on a clean rag or paper towel. Close the screw and put its little cap back on it.


Michael 95 LWB

Todd Vess wrote:

> Coming home from shopping in the city the other day, the steering began to > feel really vague in my 1990 Rangie. When we got home, I looked under the > truck and there was power steering fluid dripping onto the driveway. I > popped the hood and saw fluid all over the top of the steering rack. My > stomach sank. But, since the fluid was all on the top of the rack, I > decided to investigate further. There's a nut that's kind of like a filler > nut on the top. It was really loose, allowing fluid to escape when the pump > was running. I tightened the nut down tight, topped off the fluid and it > seems to be fine Steering is back to normal. > > My question (finally, you say), is: Is this nut some type of pressure relief > thingy? If so, should I not have tightened it down? Hopefully not, as when > it's loose it leaks. > > 

Todd Vess > 

Windsor, Colo. > 

1990 Range Rover > 

1993 VW EuroVan

To: <rangie-l@bigyellowdesign.com> Subject: RE: [RR] ZF Power Steering pumps

I have no direct knowledge of any Classic RR. I see from the manual that a Diesel RRC appears to have an Hobourn-Eaton series 500 pump, with the following characteristics: Operating pressure - straight ahead position - at idle 7 bar (100 p.s.i.) maximum Full lock (left or right) at idle 28 bar (400 p.s.i.) minimum Full lock (left or right) 1000 rev/min 70-77 bar (1000-1100 p.s.i.)

The pump ... is an eccentric roller type and also houses the pressure regulator and flow control valve. This is different to the pump I was asking about, but on the other hand, your pump appears to be described, with simple diagram, in the manual. The Pressure regulator and the flow control valve are clearly described. Note that the pump may, I repeat MAY, have another valve which simply isn't mentioned in the Manual description, as it plays no part in the normal operation of the pump. It was this unmentioned valve that was stuck open in my pump.

You say that after a period of riding the problem nearly disappears. I suspect the problem is there all the time, it is just that it is easier to turn the wheel while the vehicle is moving fairly fast, compared to the slow speed when parking, which is when you notice the problem again. Also, when driving in top gear, on main roads, you only move the wheel slightly, not as much as when you are parking. In my case the relief valve was stuck open, thus there was little effective pressure going to the box. Yours might be the same. I think that old, slightly thicker oil, thickened again by being very cold, caused the high pressure necessary to force the relief valve far enough to jam it. A contributory factor was wear on one side of the valve. It think this allowed it to be tilted over at an angle within its housing. In my case I replaced the fluid, and turned the valve through 180 degrees to allow a new part of the valve to take the wear. Although I had the idea that a stuck relief valve was the problem, I didn't correctly identify the relief valve, nor the fact it was jammed out of position, when I initially stripped the pump. Having pointed out the possibly unmentioned valve to you, it should find it easier to do the clean, strip, inspect, and rebuild that was my intention. There is a comprehensive fault finding guide in the RRC Manual. Go through it and see what clues that gives you, although it is difficult if you cannot measure the pressure. I bleed my system, and the fluid came out slowly, not as though it had a lot of pressure.

Bottom Line. I guessed there was no pressure, so I set out to open the pump and see what I could see wrong. Eventually I found it. I suggest you also remove and open the pump. I didn't need to damage any seals, and there were no gaskets. I suspect, as the operating pressures are similar, yours will be the same in that respect.

Good Luck.

- - David, Derbyshire, UK. '95RR2 - 2.5DT


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