Problem: Binding, poor returnability, noise, no assist to either or both sides, vibration or leaks.
Cause: Contamination from defective components or hoses is blocking fluid flow through the spool valve of the steering unit.
Solution: When replacing any steering component, it is recommended that power steering lines be replaced if more than four years old or they appear damaged. Also, flush the entire system with new fluid to wash away any contaminates. If you do not flush the system and replace lines, you could experience a return of the symptoms. Failure to properly service the power steering system will VOID THE WARRANTY of the replacement part.
Some manufacturers recommend an annual change of the power steering fluid to increase the longevity of the system.
Be sure to check any steering or suspension component that may be placing an abnormal load on the system. Check steering input shaft coupler, outer tie-rods, ball joints and upper strut mount bearings (if so equipped).
Courtesy of Cardone ProTech