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shade tree mechanic - power steering oddity

shade tree mechanic - power steering oddity

shade tree mechanic - power steering oddity

(OP)
A friend has a Chrysler PT Cruiser which recently suffered a power steering leak.
He took it to a local garage, where they replaced the high pressure hose, then the pump.
It leaks at the p/s pump high pressure fitting. The fitting has an o-ring, rather than metal-to-metal seal.
After changing the hose and pump, the mechanic tried different o-rings. Still no joy.
I thought these pumps would have a pressure relief valve to prevent overpressuring the system, but maybe not?
Our best guess is that the rack is not permitting flow at all and the pump overpressures the fitting, blowing past the o-ring.
The shop's only proposal is to replace the rack. It is a 4 1/2 hour job, hence not cheap.
Thoughts?
I think the mechanic is capable and the shop is honest.
If the rack did stop flowing fluid, would that cause an overpressure situation, where the o-ring at that fitting would become the weak point?
(better a leaking o-ring than blowing a hose open, I guess)
...

Jay Maechtlen
http://www.laserpubs.com/techcomm

RE: shade tree mechanic - power steering oddity

How is the steering feel?

RE: shade tree mechanic - power steering oddity

<edited>
Yes, there is a pressure relief valve in the pump, it's actually how they work - the rack is fully pressurised all the time, when you turn the steering wheel it actual vents the rack on that side, via the torsion valve, and applies full pressure to the other. This is why the feel is so good, there are no significant time delays, but also why they are so inefficient, you are pumping oil across the pressure relief valve continuously.

https://www.forbbodiesonly.com/moparforum/attachme...

https://slideplayer.com/slide/6119738/18/images/64...

https://www.freeasestudyguides.com/graphics/power-...




Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: shade tree mechanic - power steering oddity

Which is why the last two cars I've owned, my 2013 and 2021 GMC Terrains, have had electric steering as they help with engine efficiency and improved gas mileage.

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

RE: shade tree mechanic - power steering oddity

I've never seen a PS pump that ran at full pressure all the time. It's just idle pressure but full flow. The steering valve diverts flow to "push" the steering one way or the other when the wheel is turned. You only get full pressure when the steering is restricted enough, usually at the end stops if you keep trying to force it.

Test it with the return line directed to a container. The reservoir should be empty by the time the engine has started and is idling.

Try another o-ring type besides rubber. Check with a hydraulic supply company, they likely have them in stock. Or, try a green o-ring for the AC system.

RE: shade tree mechanic - power steering oddity

Quote (Jay)

I think the mechanic is capable and the shop is honest.

A capable mechanic doesn't troubleshoot by randomly replacing components for no reason.

An honest mechanic doesn't find a way to trick the customer into directing him to do unnecessary and expensive work.

RE: shade tree mechanic - power steering oddity

Lionel, nope. here's the torsion valve at 0 SWA, both sides of the piston are pressurised. It isn't full pressure typically, as the resistance of the small on centre gap is significant and there is an bleed back to the reservoir. Citreons used to have a very high on centre pressure, the downside is very little on centre feel.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: shade tree mechanic - power steering oddity

But you are right about the pump pressure, it doesn't crack the relief valve at idle, when straight ahead. it does at zero flow ie full lock which I suppose is obvious given it is fixed displacement pump.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: shade tree mechanic - power steering oddity

When I posted there is an idle pressure, idle meant the steering is not in use, not the engine idling. The idle pressure is much lower than the relief pressure, possibly an order of 10X lower. I somewhat recall 100-200psi as the typical idle pressure, but I'm not positive about that.

RE: shade tree mechanic - power steering oddity

Yup 200psi , 0 SWA idle, compared with a pressure relief valve setting of 1400 or so. I've been trying to find boost pump performance curves with no luck. Of course the first steering engineer I asked has only ever worked with electrons!

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

RE: shade tree mechanic - power steering oddity

(OP)
Funny thing is, both the original and replacement pump behaved the same way.
I think they said it leaked without turning the wheel, so that should have tipped them off that something was strange. But even the 100-200 psi would make a mess if a hose or connector goes bad.
Having replaced the hose and finding the leak still present, one could assume that the pump had an issue. There's enough labor in installing the hose, they may have thought that it wasn't worth re-installing the old hose.
And when repairing an older vehicle, you really don't budget for extensive diagnosis or research.
With new hose and pump - that is a wth moment.
I would expect the pump to have a pressure relief valve. The hose should withstand the pump's max output if the relief valve is working correctly.
Are we sure that Chrysler didn't cheeap out and build the system without a relief valve in the pump?
Right now the system has pissed out its fluid and is running without power assist. Since it is a small vehicle, steering effort is manageable.


Jay Maechtlen
http://www.laserpubs.com/techcomm

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