Steering hydraulic pressure adjustment?

Question

Hi. My new 2004 Chevy TrailBlazer steers sharp, but there is no feel in my hands at the wheel. I thought perhaps that the problem is excessive hydraulic pressure. TrailBlazer's "vague" feeling at the wheel also was remarked about by Car and Driver Magazine.

The hydraulic system for the steering must contain a pressure regulator, correct? Otherwise the hydraulic pressure would vary with engine RPM. Is that pressure regulator integrated in the pump or is it a separate component? And is it adjustable? If it's not, can it be disassembled and modified in some way so as to produce 25% less pressure?

Note: adjustable pressure regulators usually contain some kind of internal spring; the more you tighten down on that spring, the more it becomes preloaded, and the greater the output pressure of the fluid.

Mike Behnke · Accepted Answer

I would think that the amount of pressure in the steering system would not affect the "feel" but the amount of "play" in the system when traveling over uneven ground, with lower pressures resulting in more "play".

Sounds more like an > Hi. My new 2004 Chevy TrailBlazer steers sharp, but there is no feel in my

Knack · Answer

If the brake fluid was air, not hydraulic oil then I suppose your first explanation might be valid.

Yes, it's a design flaw if the steering system's oil pressure is nonadjustable. And yes, tire inflation and tire profile (height) both do relate to steering force, but it can't be blamed on the tires. Any tire would certainly require *more* steering force if it was underinflated, and that problem is exacerbated by tall profile tires, so you could deduce that the reverse is also true. However, P245/70R16 tires are not taller than what's standard on most SUVs. The steering system is designed for the specified tire size, their normal inflation, and the vehicle weight, among many other factors.

Robert Hancock · Answer

There will be a pressure relief valve in the pump - on this vehicle, itseems to be specced to open at 1500 psi and is not adjustable.

Knack · Answer

A pressure relief valves is a redundant safety device set at a pressure slightly above the normal operating pressure range. I doubt if that valve cycles open/closed to maintain 1500 psi at the steering actuator.

There must be some other (internal) pressure regulating valve that's built into the pump.

Robert Hancock · Answer

It's actually called a "power steering pump flow control valve" - it's aspring-loaded bypass valve that's screwed into the pump housing. That's theonly pressure-regulating device I can find any mention of, and it's notadjustable (really, why would it be?)

Knack · Answer

news:hQeWb.465332$X%5.127924@pd7tw2no...Thanks, Bob. OK then, that's the pressure regulator valve. I can understandwhy the engineers wouldn't have selected an adjustable one, as it's not*imperative* to have adjustability, and a fixed pressure one would be lowercost than an adjustable pressure one.I'm glad at least that it's an external component to the pump (notintegrated in the pump). I believe that I can replace it with an adjustableone available from either an industrial supplier or fluid power componentsdistributor.In fact, I've already found one (Prince RD1850H) available at Grainger for$33 It has a 1000-2500 psi adjustment range. That one should be able toproduce a satisfactorily lower actuator pressure than 1500 psi chosen byGM's engineers. Of course I'll need replacement fittings and tubing toaccomodate the replacement valve. The existing valve, tubing and fitting canbe removed undamaged for future reinstallation if necessary.

Steering hydraulic pressure adjustment?

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