Internal leakage in the spool valve of the rack and pinion assembly. If you want to prove this cause, find a mechanic with an inline pressure tester. (They aren't common). It is inserted between the pump and the rack. The tool has a pressure gauge and a shutoff valve. With the valve open, if pressure is normal, (up to 1100 psi), the pump is working. If pressure drops when turning the steering wheel and there is no power assist, there is internal leakage in the rack.
If the pressure is low, the valve is closed for just a few seconds to isolate the rack from the pump. If pressure rises rapidly, the pump is working. If the pressure remains low, the pump is worn out. Some pumps, the tiny "ZF" style for example, experience rapid wear of the plastic vanes in the impeller. The clue to that type of wear is the power assist will return as soon as you raise engine speed just a little over idle speed.
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Wednesday, November 24th, 2010 AT 8:57 PM
