Power Steering Trouble Shooting Guide
Determining The Fault
 
Understand The Fault
 
Before attempting to fix any problem it is obviously most important to fully appreciate what is it you are trying to fix. Noisy pumps, leaks or no assistance are obvious, however, if the complaint is one of road performance, i.e. wandering, steering kickback, darting etc. you must know exactly what conditions will bring on the fault. It is useless reading a job card which loosely describes a steering fault. In these cases you must talk to the driver or owner of the vehicle.
Determining if the fault is Air
 
Air in the hydraulic circuit will cause many problems such as, steering kick back, valve and bearing damage, noise and oil loss from the reservoir. Pre supposing that the system has been correctly bled in the first place, air can only enter the system through two points. One, through the pump shaft seal. Two, the reservoir to pump supply line. The pump shaft seal, in some pump designs can be under negative pressure. A faulty seal in these cases will not leak oil out but will let air in.

 
Determine if the fault is Hydraulic
 

Noise

Gear or buzzing noises mostly emanate from the pump although it's source can sometimes be deceiving. Worn pumping elements, i.e. gears, end plates and vanes, can generate high frequency hydraulic pulses which are transmitted throughout the system. These high frequency pulses act on all internal surfaces producing noise. A noise generated by the pump can be radiated by the steering gear or steel pressure lines.

A hiss generally indicates leakage and is only evident under pressure. Pump relief valves are an acceptable source as are partially closed power steering gear valves. Worn components will also cause high pressure internal leakage, and consequently noise.

Temperature

Normally power steering systems should not get much above 80C. Excessive temperature is an indication that there is internal leakage, excessive flow or a restriction. Excessive flow or restrictions will cause the system back pressure to be high, say, over 520 kpa (70+5 psi). High temperatures will harden seals, and in some cases, If high enough, anneal tempered or hardened metal components.

Lack of assistance

Lack of assistance is usually due to lack of pressure. Low pressure can result from pump faults, steering gear valve faults or internal leakage. Some steering gears have adjustable lock limiting valves which dump hydraulic pressure just prior to full left or right lock. These valves are simply externally adjustable plungers which unseat a valves, usually at each end of the piston. These valves, when unseated, can trap contaminants and then leak, not allowing pressure to build up on one lock.

Slow or Jerky Steering

Steering should be able to be applied at the rate of at least 1 steering wheel turn per second. This requirement is to ensure that there is sufficient steering speed for evasive manoeuvres. Low pump flow rates will limit steering speed. As the piston moves the pump must supply fluid in sufficient volumes to maintain the pressure required to overcome steering resistance. The effect of low pump flow rates may be initially be felt when rapidly applying steering during slow speed manoeuvring at low engine rpm.

To determine if the pump is at fault try to apply steering at the rate of 1 steering wheel turn per second with the engine at idle. If the steering is knotty or jerky raise engine rpm and if there is an improvement then a faulty pump or pump drive is indicated.

Leakage

Leakage can be classified as internal or external:

Internal leakage - Is leakage past valves, piston seals, pumping elements etc. Internal leakage will reduce the output of the steering gear.

External leakage - This is just what it means, oil on the floor.
 
 
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