Stunned.. The fault is beyond me lol

[power-steering]

Today I had a customer come in with a nice Mercedes C230 Avantgarde.

It's come in because every now again the steering wheel just wants to throw you at full pressure and really lock up one-way. - Very dangerous to drive really..

From what it sounds like and felt like, we assumed it was the power steering pump because we've had this problem before.

Also when the cars cold, power steering is working lovely, soon as it heats up and you turn the wheel lock-to-lock about 10 times it starts to get heavier but when driving that's when it gets dangerous like it just doesn't want to go where you want it to i.e. body roll!.. wants to swing itself round the corners rather than dip round.

We took the pump off and fitted it to our test rig but much to our surprise it was pressurising normal between 1000-1200psi. Even on high pressure we achieve 1600psi which is powerful enough to run a Rolls Royce Rack on!!

Opened it up and checked it all out, everything was spot on (why wouldn't it be, it's a new car..) but we had to query it.

Put it back on test, pressure still good.. left it running for an hour on test rig, held pressure beautifully.

So we've put it back on the car and problem remains, we then removed the rack and tested that - again nothing wrong with it.. even the pipes were fine, no restrictions.

Customer has gone home tonight and the problem remains I want to help him so I've asked him to join this forum but I too would like to know what's going on. I remembered something about cambers being really sensitive and suspension leaks so I've given those advisory notes to him to have checked out.

He did mention he went and got it tracked, but then a few miles later the steering wheel was slightly off-centre again..

Any ideas? It's definitely nothing to do with his power steering system.

 

[television]

Does it have speed sensitive steering, the first 6 vin numbers would help

 

[jberks]

Sounds familiar actually!
Mine, every now and again, if I'm working though a car park (lock to lock and back on idle) seems to run out of puff. I've always assumed the pump's just not up to dragging 245 tyres around and was designed for something thinner but I did nearly hit a car on the way into a spot once when twirling the wheel became a weightifting task. Stopped for 1-2 secs and all is well again.

 

[brandwooddixon]

Two points spring to mind, which you may have covered already.

Belt slip and overpressure valve.

 

[wireman]

A suggestion, I do not have any experience of this models steering equipment but,

Methinks its your steering rack/box at fault.

Within the steering system there hides a "normal" rotary to linear motion convertor ie the rack and pinion or old fashioned worm and nut, these will move the steering directly wthout the hydraulic power being applied, it is of course much harder to move the loaded steering without hydralics but it will move.
In addition to the normal steering gear there is a hydraulic cylinder that operates the steering in addition to the motion of the rack or box, in a rack its mounted alongside or at the end of the rack, in a box its mounted within the worm and nut assembly.
On comercial and big vehicles the cylinder is often a seperate entity connected by a drag link to one track rod. The cylinder provides the assistance we all know and love.

To control the cylinder's assitance pressure there is on the steering input shaft (between steering wheel and steering mech input) a torque actuated hydraulic 5 port proportioning valve which will allow pressure from the pump to act upon the hydraulic cylinder.

In operation at straight ahead or any other no assitance required position the valve applies equal low pressure to each side of the assitance cylinder, cuts off the pumped flow to the cylinder and allows fluid to return to the pump reservoir having done no work.

When a demand is made that the steering angle is changed the valve senses the input shaft torque and sends fluid to that end of the cylinder which will provide assistance in turning the steering, the opposite end is connected to the return pipe, when the desired angle is achived the valve cuts the flow and ceases to provide hydraulic assistance to the steering.
On returning the steering to centre an opposing torque is applied to the valve and the same functions occur but at the opposite ends of the cylinder again untill the desired angle is reached.

The control valve is usualy integrated into the input shaft (pinion or worm) just inside the steering box/rack assembly and is of an exteremly fine construction with small slits that become covered and uncovered by very small angular deflections of the input shaft, They are metering slits and give well controlled hydraulic flow rates dependent on the amount of torque on the shaft, a small torque gives a small hydraulic assistance and vise versa up to the maximum the pump can provide, be this either by pressure limit or flow rate limit. The speed sensitive feature of some systems is provided by controling the flow and pressure available from the pump in accordance with some parameter derived from road speed and the requred modifications to assistance rates.

My suspicions are

A/ that some forign body has entered your system and taken residence in the valve, causing incomplete control of the cylinder pressure.

B/ a seal within the valve is leaking on occasion and again causing incomplete control.

C/ if its worm and nut, a seal on the nut (which forms the piston) is intermittently leaky.

D/ plain old wear and tear but I don't think that's too likely.

E/ water in the fluid (it goes pink) rusting the sufaces of the valve body.

The control valve metering slits are very small and a piece of anything that the Mk1 eyeball can see is suffient to restrict them, so my strongest feeling is for forign body damage.
There may be a chance if it is a filth particle that fully emptying the system will dislodge the blockage but getting all the fluid out of a hydralic system is near immpossible without totaly dismantling all parts of that system.

The question remaining (if it is filth) is where from? so that could be, wear and tear in the pump or bad servicing including failiure to renew filters or just a dirty hand or oil bottle adding the muck to your resevior with some nice clean fluid, there is always the possibility that its been there since manufacture and has become dislodged from where ever it was hidden.

I cannot think of anything other than control valve trouble for this fault and the cure may well end up as replace the steering rack or box along with verification of total (operating theatre) cleanliness in all the other hydralic parts including the pipe work, flexible hoses and connections.

 

[power-steering]

We've had the valve pinion out of the rack to check for any bits, no contamination in the oil, no leaks (holds pressure perfectly lock-to-lock) and the rack is spot on, it flicks the pressure gauge the instant we touch the valve so it's working perfectly.

It does have speed sensitive steering..

I told him to check his cambers/suspension because I read in another thread someone had similar issues and something was mentioned about the avantgarde having very sensitive cambers.

 

[television]

Do you have WIS

 

[power-steering]

nah I took no details from the car.. just it's a late c230 avantgarde

 

[television]

There are faults like you describe for speed sensitive steering in WIS

 

[Xtractorfan]

Two possibilities from my point of view, one the valve is opening fully and allowing full pump pressure to control th system, or too much pressure build up in the pump.
I would as a matter of course and interest change the PS pump in order to check/eliminate that possibility

 

[power-steering]

ah right, what like faulty sensors?
We don't get many of these new c230 sensor racks in but the ones we do, sensors seem to work fine just leaky racks or bent rods where they wack the curbs.

Will have to look out for that for next time, made a note on the system for it

 

[television]

I will try and look up thew listed faults

 

[television]

I could send you the info Info if I had your Email address

 

[BlackC55]

It also sounds like a wheel alignment issue rather than a PS pump problem.

 

[power-steering]

Yeah I agree, definitely not power steering problem. Our email is info (at) power (hyphen) steering .co.uk

Any emails just mark for the attention of Jay in the subject line

Cheers mate,
Jay

 

[television]

Yeah I agree, definitely not power steering problem. Our email is info (at) power (hyphen) steering .co.uk

Any emails just mark for the attention of Jay in the subject line

Cheers mate,
Jay

I cant add an attachment to that,I tried, its a useful paper on your fault

 

[power-steering]

Oh :s.. not sure why, I receive many attachments to this email. info"at"power-steering.co.uk

 

[television]

Well put it this way,I do not know how to then

 

[power-steering]

It's okay for now really. You guys been much help. Customer still hasn't got back in touch I said I would find out what I could and he said he'll ring back by thursday/friday. If he does, I'll tell him to sign up (which I already did as well).

Cheers guys,
Jay

 

[carmania11]

I have also tried the same thing.