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Power Steering Problem

Hey guys,

Awhile ago i had power steering put in my HQ ute. Since then it has made a loud screeching noise when I turn the wheel to full lock. What is happening? Is it doing any damage?

Thanks,

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When you turn the wheel the p/s pump gets a whole lot harder for the engine to turn and if the belt is loose it will start slipping. This might cause the noise.
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When the unit gets to full lock the oil has to go somewhere.Not sure about it doing any damage though.
Cheers Scotty.
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Cheers Scotty.
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Thanks for the ideas guys, I'll check em out

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Yep, loose or worn belt.

At centre, power steer pumps put out about 0 psi, at ½ lock they put out about 400 psi, at full lock they put out about 1,000 psi...this is why the belt squeels at full lock - the pump is working hardest at full lock.

If you also get shudder through the wheel at the same time, your steering needs bleeding.

Cheers...Dave

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Cheers...Dave

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Dave,

I never thought I would see the day, but some corrections are due.

The amount of pressure at the output of the power steering pump is not determined by the immediate position of the wheels (i.e amount of lock).

What does determine the pressure is the amount of “error

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You're absolutely right,
the belt was a little loose so it's all fixed now.
Feel silly for not checking that myself!

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In any car, new or old, you should turn to full lock, then turn back a fraction of a turn until the noise stops. You won't lose turning angle, and you're taking pressure off the system.

Even new cars make a noise of such on full lock... turn it back a fraction and it stops.

Cheers,
Jason.

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You have to back off slightly at full lock, as there is full pressure on the system with nowhere for the oil to go, this can cause damage to the system,,,,
Cheers

john
Silence is Non Committal
MY SHED

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Cheers
John
:o)

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Old wives tales...

In any dynamic hydraulic system, the oil must have some place to go. Power steering systems use vane pumps, which are positive displacement.

If your statement "there is full pressure on the system with nowhere for the oil to go" was correct (which it is not) then immediate damage will be done which will cause the power steering to fail.

The reason your statement is not correct is because there is a pressure relief valve at the output of the pump which diverts fluid back to reservoir. This is where the fluid goes when turned hard to full lock.

If the belt is tensioned correctly, most of the noise at full lock is a result of the pressure relief valve operation.

There is absolutely nothing that can cause damage to the power steering system if the wheels are held at full lock. The pump is working harder, that is for sure, but the pump and the rest of the system is designed to handle pressures at least up to the setting of the pressure relief valve.

Brett.

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My above comment was a generalisation, of course it has a pressure relief, it would explode if it didn't, the oil has nowhere to go within the steering and the extra pressure put on hoses, seals and steering components (which btw can be damaged) can be avoided by simply backing off from full lock,,
but hey, if you don't care about your steering, then knock yourself out,,
:)

Cheers

john
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Cheers
John
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John,

Firstly, I don't condone any abuse of any mechanical equipment, be it a car or otherwise. Everthing is designed to operate within certain limitations.

To clarify the point of this discussion, the power steering CAN be damaged IF the steering wheel is repeatedly forced violently into the full lock position (or against any other form of resistance). This practice would obviously constitute intentional abuse as viewed by any reasonable person. The component that may suffer damage is the torsion bar in the valve, which may result in it being set with a permanent twist. This damage is not a result of any hydraulic force, it can even happen with the engine stopped.

Nothing can be damaged by simply holding the steering wheel evenly at the full lock position.

Every part of the power steering system is designed to withstand the maximum force that can be applied to it by the hydraulic system, ultimately limited by the setting of the pressure relief valve in the pump.

This means that as long as the pressure relief valve is working properly, and set correctly, there is no way that any hose or seal can burst or blow out or any shaft or other component can bend or break by holding the steering at full lock UNLESS the part was faulty, worn or damaged in the first place.

My suggestion (and something I do from time to time), is next time you are servicing your car, turn the wheels gently in to full lock and hold it there for 10 to 15 seconds.

If there are any leaks or blown hoses, they needed replacing anyway. Best to find out you have a problem in the comfort of your own shed, rather than 400km away in the bush at midnight.

Of course, if you want to be really kind to your car and make it last forever, don't drive it at all.

Brett.

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Anything that can be done to lessen the wear and tear on any components has to be a good thing yes?
I beleive that holding the steering at full lock is unecessary and causes extra wear and potential for damage that can be very easily avoided, you lessen it's life by over working it,, (and that is all I am trying to say here, that you CAN damage it),, you have your opinion, and I have mine,,,,
:)
Cheers

john
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Cheers
John
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Hi Brett,

I typed this out at about 12:30 last night and then oldholden had a seizure and it didn't go through and I had to go to bed...

OK. First, I know lots of stuff but I don't know everything and sometimes I remember stuff wrong. Feel free to challenge. Sometimes, the best knowledge comes from teh discussion following a challenge to an answer and THE most important thing is that the person gets the correct answer to their question.

Secondly, thank you for your explanation of how power steering works internally. That is one thing I have never really sat down and studied so that I understand it completely. I now understand it MUCH better from your post. :-))

My information above comes from the GMH HQ manual. What I didn't say is that the pressure is a momentary pressure, sorry :-)

When checking a power steering system, a gauge is hooked into the high pressure hose, the wheels turned to full lock and the pressure measured, If it is less than 900 psi, the hydraulic system of the steering needs to be overhauled. Then there are secondary checks listed to further diagnose where the fault may lie.

HQ - WB power steer systems will have about 1,000 psi (momentarily) at full lock, up to 400 psi at about ½ lock (momentarily aagain) and bugger all at the straight ahead. The momentarily bit is with the car stationary.

IMHO, the reason that power steer belts tend to squeal at full lock is due to the car moving and the steering trying to self-centre. As the tyres get further away from straight ahead towards full-lock, there is more pressure trying to return them closer to centre (depending on the geometry and alignment of the front end, some are better and some are worse). This extra pressure trying to move the wheels back to straight ahead means the pump has to work harder (put more pressure into the system) to keep the wheels turned and this puts more pressure on the belt which has a greater tendency to slip and squeal.

Cheers...Dave

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Dave,

I can understand the 900-1000 psi specification at full lock, this is obviously testing the maximum pressure output of the pump itself, and also the operation of the pressure limiting device in the pump.

I would assume the 400 psi reading at 1/2 lock is a result of the average many variables (e.g. friction of tyres on the ground, how fast the steering wheel is being turned at that moment, and steering geometry).

One thing is certain. If the car is stationary, the wheels are turned to any position and then the steering wheel is released, as long as the steering wheel remains stationary the pressure in the system will be almost zero.

On the other hand (as I have said before) maximum pressure, the same as at full lock, can be attained with the wheels pointed straight ahead (or any other position) if there is something preventing the wheels from turning (e.g. against a gutter) and the steering wheel is turned in an attempt to overcome the resistance.

Brett.

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Quoting bf6379:
"The component that may suffer damage is the torsion bar in the valve, which may result in it being set with a permanent twist. This damage is not a result of any hydraulic force, it can even happen with the engine stopped."

What if the hydraulic system fails or the belt breaks and you have to drive it for a bit with no power assistance? The torsion bar thingy that controls the proportioning valve would have to take the full force of my oh-so-muscley arms ;-) Doesn't this valve and torsion bar setup have some kind of angular displacement limiting stop to limit the strain on it?
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It does have limiting stops. Normal driving with no hydraulic assistance should not damage it. However, repeated shock treatment can deform it.

Many years ago my Dad had a Triumph TC2500 with power steering. Mum hit a concrete pylon in a carpark with the drivers side front wheel taking most of the impact. The shock through the steering was enough to put a permanent twist in the torsion bar. The result was as soon as the engine was started, car stationary and hands off the steering wheel, the steering wheel would turn all by itself until it hit full lock.

Brett.

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