The steering rack, in your rack-and-pinion equipped vehicle, provides precise steering control with a minimum of moving parts. The light weight and durability of this design makes it favoured among manufacturers of cars and light trucks. The basic system consists of an input shaft and gear -- the pinion -- and a horizontal shaft and gear -- the rack -- in a sealed housing bolted to the frame or unibody of the vehicle. Power-assisted units contain a spool valve on the pinion shaft to provide power steering assist.
Block the rear wheels, using wheel chocks, to prevent vehicle movement during the test. Set the parking brake firmly. Slide a floor jack under the front subframe for front-wheel drive vehicles or cross member for rear-wheel drive vehicles.
Raise the front of the vehicle, until the wheels are off the ground, using a floor jack positioned under the front cross member or subframe. Support the weight of the vehicle by lowering it onto jack stands positioned under the frame or cross member.
Start the engine. Observe the front wheels. If the front wheels begin to turn on their own with no steering input from the driver, replace the steering rack unit. This condition is caused by a sticking spool valve in the rack and pinion assembly. Turn off the engine.
Move the wheels back and forth by hand, from the three o'clock and nine o'clock positions on the tire, and observe the tie-rods that connect the steering rack to the steering knuckle near the wheel. Any perceptible movement, with reasonable hand force on the tie-rod joints, indicates the need for the replacement of tie-rods.
Remove the front wheels using a lug wrench. Loosen the clamps on the bellows boot, located around the inner tie-rod and the rack and pinion housing, using a screwdriver or socket and ratchet. Slide the bellows boot towards you until it slips from the housing. Inspect the interior of the boot for excessive power steering fluid accumulation. Slight seepage around the seals in the housing is normal, but an accumulation of fluid in the boot requires the replacement of the rack and pinion unit.
Pry the dust boot that covers the pinion shaft connection to the steering column sector shaft, located on top of the steering rack, from the steering gear housing, using a large flathead screwdriver. Inspect the pinion seal for leakage. Replace the rack and pinion unit if the pinion seal is leaking. As with the rack seals, seepage is normal, but an accumulation indicates a leak and indicates that replacement of the rack and pinion unit is required.
Raise the vehicle from the jack stands, remove the stands, and lower the vehicle until the wheels touch the ground. Have a helper turn the steering wheel back and forth while you observe the pinion shaft. If the pinion shaft moves without causing movement at the wheel, replace the rack and pinion unit.