Power steering is a wonderful invention, especially for those who lack upper body strength or have puny arms. Years ago it was considered a luxury option mostly for elderly people who drove big cars. But today, everybody wants effortless steering, whether they drive an econocar or a three-ton SUV. Consequently, virtually all cars are now factory-equipped with power steering as standard equipment.

When high pressure fluid from the power steering pump enters a steering rack, it is routed through "spool valves" connected to the steering column. When the driver turns the steering wheel, the spool valves open ports that direct pressure to a hydraulic chamber around the rack. A piston on the rack bar divides the chamber into two halves, and pressure is channeled into one side or the other depending on which way the driver is turning. This provides power assist and helps push the rack bar in the desired direction.

Normal operating pressures within a power rack generally do not exceed 150 psi when the wheels are straight ahead. In a turn, pressure can climb to as much as 700 psi or higher depending on how much assist is needed. That's why the seals must be leak-free.

WHEN TROUBLE STARTS
The first sign of leakage may be a telltale stain in the driveway. Or, the vehicle owner may notice the fluid inside the power steering pump reservoir keeps disappearing. If the fluid level gets too low, the pump may suck in air causing...