A vast majority of damage to the power steering system is caused by contamination of the fluid. Minute, mostly metallic particles, are pumped throughout the system with the power steering fluid. The abrasive action of these contaminants will damage seals, score shafts and power bores and foul the valve assemblies. Naturally, as the power steering system is a sealed system, the only possible source of these contaminants is from within the system itself and the number one culprit is of course, the power steering pump.
The major source of these metal particles is the cam and rotor of the power steering pump. These particles eventually find their way into the seal area of the rack shaft, where they damage the seals and cause the scoring of the shaft, resulting in fluid leakage into the rack boots. These same metal particles can find their way into the pressure valve, eventually jamming it. This can result in either partial or total loss of power assistance to the steering.
Additional sources of fluid contamination can include perished or deteriorating hoses. In the same way that metal particles can be transported throughout the system, so too can particles of rubber from the aging hoses. These particles can become jammed in the pressure valve or the rotary valve, with partial loss of power assistance being the likely result.
As always, the greatest cure is prevention. Few manufacturers recommend a service schedule for their power steering systems, creating a tendency for regular fluid flushes to be neglected. If the fluid in the power steering reservoir has changed to a grey colour, it may already be too late. The grey colour is caused by fine metal particles, held in suspension in the oil. They have already been pumped throughout the system, effectively becoming a grinding paste on any of the moving parts within the system.
The answer is of course, to regularly service the system. Flushing the power steering fluid completely every 12 months or 20,000 kilometers and fitting a return line filter will go a long way towards ensuring the longevity of all components within the system. A return line filter will not prevent the pump from wearing, but it will prolong the service life of the system by filtering the contaminants from the fluid that accelerate that wear. (Excerpts from Tech Talk - VACC Technical Services)
Do you have any of the following symptoms in your vehicle?