Repair Guide: Power Steering

Most cars today are equipped with a power steering system. Many power steering systems use hydraulic power. These systems use a power steering pump driven by a belt from the crankshaft. The pump moves fluid under pressure through hoses to the steering gear. The pressure is used in the steering gear to reduce steering effort. A reservoir for fluid is attached to the rear of the pump. Checking the fluid level in this reservoir is a common under hood maintenance job.

The fluid used in the power steering system must be the correct type for the vehicle. Always check the owner's manual for the correct type of fluid. Older vehicles use automatic transmission fluid in the power steering systems. New vehicles use special power steering fluids. These fluids meet the special requirements of the power steering system. They are often a different color from automatic transmission fluid so that leak detection is easier.

Q & A: Power steering

1. My steering feels loose. Any idea why?

Answer:

The most common causes of steering looseness include worn tie rod ends, a worn idler arm or center link (on vehicles without rack and pinion steering), a worn steering gear or a worn steering rack.
Normally, your steering wheel should have no more than about a quarter inch of play. Any more means something is worn or loose and needs to be fixed.

WARNING: Don't put off having your steering looked at because a failure of a critical component could cause loss of steering control!

The inner and outer tie rod ends should have no perceptible looseness. Worn or loose tie rod ends are especially dangerous because if one pulls apart you'll lose steering control. Worn tie rod ends can also cause rapid tire wear.

If you have a rear-wheel drive vehicle with conventional steering (not rack and pinion steering), the idler arm should have no more than the specified amount of maximum play. Refer to a manual for the specs and recommended procedure for checking it. Checking idler arm play usually involves pulling on the arm with a specified force and measuring how much the arm deflects.

If your vehicle has a lot of miles on it, the steering gear or rack itself may be worn. On conventional steering boxes, there's usually an adjustment screw that can be used to take some of the slack out of the system. With rack and pinion steering, though, adjustment is usually little help because the rack develops center wear. If the pinion is adjusted to compensate, the rack may bind when turned to either side. The only cure for a center wear condition is to replace the rack with a new one (an entire new rack assembly).

OTHER CAUSES

Sometimes the steering will feel loose because of a worn U-joint coupling in the steering column. Loose or worn wheel bearings can also make the steering wander and feel loose.

2. Power steering feels stiff when I first start the car, but feels normal after I've driven awhile. Why?

Question:

My power steering feels stiff when I first start my car, but then feels normal after I've driven the car awhile. How come?
Answer:

This is called "morning sickness" and has nothing to do with being pregnant. The condition is caused by wear in the spool valve housing on certain power steering racks -- notably GM front-wheel drive cars.
When the car is first started, the rack is cold and clearances in the spool valve are at their greatest. Hydraulic pressure from the power steering pump leaks past grooves worn in the aluminum spool valve housing. This causes a loss of pressure and increases steering effort. The steering feels stiff with little or no power assist. As the car is driven, the rack warms up. This decreases the clearances inside the spool valve housing, which reduces the leakage past the grooves. More pressure goes to where it is supposed to go and the steering becomes easier as power assist returns.

The "fix" for this condition is to replace the rack with a new one (preferably with a cast iron spool valve housing) or a remanufactured rack that has a stainless steel sleeve pressed into the aluminum housing.