This is for the w201. After I disconnected the upper hose tho the ps pump to drain it so I have access to another part, I refilled it, but now I have no power steering. Set both fronts up off ground car on/engine off and turned wheel from lock to lock to try to get out any air. Still nothing. I then opened up the pump to see if there was anything internally wrong and all looks fine. Anyone know what could be the problem? When the wheels are off the ground they turn fine, but when driving it is very difficult to turn.

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1990 190E 3.0L

I've never had this happen. Was the hose you took off a return or pressure hose?

Pressure

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1990 190E 3.0L

Did you replace the filter in the bottom of the fluid reservoir? Possible that it's gunked up enough to create an airlock and prevent the pump from sucking fluid? For giggles, you might pull the filter and see if you can get the pump to prime itself.

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Current stable:
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1983 500SL 120K (SLoL)

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1985 524TD 167K (TotalDumpster™)

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1986 300SDL (RIP)
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if the pump were sucking air - it would have been collosally noisy - the thread title would have been about not loss of steering, but more of insane noise from pump.

but you are right, priming the pump after a hose replacement job is a must, I do it by turning the pulley slowly. (I have been stung by cheap rebuilt saginaw pumps - they teach you a lot about this).

for the OP - you might want to see the pressure hose itself for restriction, the pump relief valve maybe opening too early due to a blockage in the pressure side of the pump/line.

I have once or twice seen a rebuilt hose do that and I found the crimps were incorrect. (not on MB though but its a common hydraulic assist steering design)

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

I was removing my AC suction hose and disconnected the pressure hose of the p/s to get it out of the way. When I reconnected it to the pump and filled it with ps fluid I took it on a test run. The steering was hard. I pulled over and checked the ps fluid and the reservoir was almost completely empty, save for the bit that I could see just below the filter. Went home and added more fluid, but the problem is still there. There is no loud noise or groaning from the system. Is it possible that there is air? Is there a way I can just drain the entire system and start from scratch and refill it? I inadvertently checked the pressure hose by disconnecting it and starting the car......My entire engine bay on the driver side and that half of my garage from floor to ceiling was sprayed. Can someone please advise if there is a proper way to just drain everything and start from scratch? I just resealed the ps system 12/25/15, so only 6 months ago.

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1990 190E 3.0L

the only reliable way to replace all the fluid is draining the steering box, there is a drain bolt on the older ones. The other way is to have the system drain into a bottle/bucket from the return line, dont run the pump at engine rpm as the fluid moves quite fast this way, Use a drill and a smallish belt to run the pump and replace the fluid.

If the system had air in it you would hear noise, the system is very well designed and purges out air itself unlike american cars which require a suction system to pull out air bubbles.

I beleive something got into the pressure line when you disconnected it. The pump will see this as a "pressure stop" and the relief valve will open up

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Draining and refilling won't help.

Check to see if the PS pressure hose was kinked either on the rubber or metal line. Did you put a cap over the line? I've seen lines installed with a plastic cap still installed causing a blockage.

I didnt do anythihng to the hose other than disconnect it. Plus it doesnt seem like its blocked as there is a ton of force that is pushing the fluid out. Does it make a difference that the steering seems fine when both front wheels are off the ground? I also disconnected the steering damper to see if that made a difference and got no change.

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1990 190E 3.0L

With wheels off the ground the steering pump is just idling away as there is no load, the pump applies pressure on demand and off loads when the pressure demand is too much - thats why at max lock the pump is at full pressure and the relief valve opens up.

In your situation, either there is some debris in the pressure line causing this stalling of hydraulics or the relief valve in the pump got disturbed and unscrewed while removing the pressure line or by some really oddball co-incidence the rotor in the pump has developed side clearance.

You claim you tested the pressure side, can you test the return side of the fluid circuit, are you getting smooth flow from it? The pressure side is tested with a gauge - at full bypass the gauge should be maxing out at the rated pressure of the pump.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

The system should be flushed by removing the return hose to the pump. Siphon the fluid out of the reservoir, replace the filter, fill with fresh fluid, then have a helper start the engine, move the steering wheel slightly side to side with the front wheels off the ground and another helper pours fluid into the reservoir while you direct the return hose to a pan.

I flushed a couple of quarts through which completely purged the system of the old fluid. Disonnecting the pressure hose won't flush steering gear. It's much easier to disconnect the return hose, and the fluid is at low pressure.

My recommendation is to raise the front end off the ground, start the engine, move the steering wheel back and forth gently, while a helper keeps the reservoir full. As long as the reservoir doesn't run dry during this procedure the system should bleed air, but you have to be quick because the reservoir rapidly depletes.

Duke

Does the PS pump make noise when you turn the wheel against the steering stops? ( the nose is from the pressure relief. )

MB steering gears don't use a torsion bar / rotary valve that is relatively tolerant to dirt, they use a valve and reaction ring. I haven't gone through exactly how these systems operate.

I'm not sure if your box is the same, but have a look on the 124 performance web site and here How to reseal a MB steering gear for what is inside a 126 steering box . The top pic shows where the valve is and step 8 shows it's removal.

I wonder if you didn't get a big chunk of dirt in the line and the valve is jammed.

Replaced the power steering pump and problem is now resolved. Though, I am not sure how the pump failed. It does not look like much can go wrong with it since its mechanical. When I disassembled it everything was moving freely inside and no binding of any sort. I'm puzzled.

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1990 190E 3.0L

was the pump rotor not fully seated when you took it apart? I learned that while resealing saginaw pumps, the rotor needed to be driven down hard in the cavity otherwise the pump relief port would just short circuit internally.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)

Not sure, I just put on an entirely new pump.

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1990 190E 3.0L