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 noise and a loss of power assist.
Normally, the power steering system should not use any fluid. The level should remain the same regardless of the age of the vehicle or how many miles on the odometer - unless, of course, the system is leaking.
Checking the power steering fluid reservoir regularly (as when changing oil or doing other underhood maintenance) is a good way to catch leaks early on before they cause additional problems. The level should always be checked any time a steering complaint is noted.
If the fluid level is low, a complete and thorough visual inspection of the entire power steering system should be undertaken to determine where the fluid is going.
Power racks typically leak at one or both ends where the rack bar passes through the end seals, at the pinion input shaft seal, and/or internally in the spool valve housing. Leaky end seals may or may not leave telltale stains on the outside of the rubber or plastic bellows. If the leak is really bad and the bellows are cracked or loose, you'll probably see fluid dripping from the rack and the bellows will be wet. But if the bellows are still intact and tight, you might not see any obvious signs of leakage.
Normally, the end bellows on a steering rack should contain little or no power steering fluid. Their purpose is to protect the inner tie rod sockets from dust and moisture. A few teaspoons of fluid in the bellows of a high mileage vehicle is not unusual and is not a valid reason for replacing the seals or the rack. But if the bellows contain a lot of fluid, the rack is leaking and needs to be fixed.
On vehicles that have soft rubber bellows, you can pinch or squeeze the bellows to feel for fluid inside. On vehicles with hard plastic bellows, you'll have to loosen the bellows clamp and slide the bellows back to check for fluid inside.
If you're not sure the rack end seals are leaking, or you want to verify a leak before repairs are recommended, here's another procedure you can use:
Raise the vehicle so the front wheels are off the ground.
Loosen and push back both bellows on the ends of the rack so you have a clear view of the seals on both ends of the rack.
Wipe off any dirt or oil on the rack bar.
Start the engine, and with it idling at approximately 1,000 rpm, crank the steering wheel all the way to the right stop and hold under light pressure for about five seconds. Do not hold the wheel so hard against the stop that it activates the pressure relief valve! Then crank the wheel all the way to the left and hold for five seconds. Repeat this 8 to 10 times.
Now check the rack for leaks. If you see fluid dripping from the rack, the end seals are leaking and repairs are needed. If no leaks are found at the end seals, check the pinion input shaft seal and the hoses and pump.
If a hose connection is leaking, you might be able to fix it by replacing the seals or O-rings. But don't try to fix a leak by simply tightening the hose or line connection. On some racks, there's supposed to be some flex in the connections. If you try to stop a leak by overtightening the connection, you may end up stripping the threads.
If the seals around the spool valves inside the rack are leaking, the steering may feel stiff or sluggish especially when a cold vehicle is first started. This condition is often called "morning sickness" and has nothing to do with having a baby. But your customer may have a cow when you tell them they need a new rack and how much it's going to cost!
New seals alone won't fix most internal leaks because the old spool valve seals have usually worn grooves into the inside of the control valve housing. This tends to be more of a problem in racks with aluminum control valve housings than ones with cast iron control valve housings. The only cure for this kind of leak is to replace the rack with one that has a new or sleeved control valve housing.
RACK REPAIR OPTIONS
Replacing a set of leaky seals with new ones would seem to be the most logical and easiest way to repair a leaky steering rack. But seal kits are very hard to find, and often cost almost as much as a remanufactured rack. In researching this article, we called half a dozen auto parts stores to see if anybody carries seal kits for racks. None did.
One reason why auto parts stores don't carry seal kits is that few shops attempt to rebuild racks themselves. High mileage racks usually have multiple problems, such as worn rack bars and gears. Corrosion or scratches on the rack bar will quickly ruin a new seal. Attempting to sand or polish out a rough spot on the bar only makes matters worse by creating a low spot that leaks even more when it slides back and forth under a seal. That's why it's faster, easier and less risky to simply replace a rack if it is leaking or worn.
A quality remanufactured rack should be pressure tested to assure it is leak-free, and come with a warranty to protect you in the event of a comeback.
If you find a leaky hose, or hoses that are cracked, rock hard with age, deteriorated and mushy feeling or otherwise damaged, replacement is the only cure.
Power steering systems have two types of hoses: a high pressure supply hose that carries pressurized fluid from the pump to the steering gear, and a return hose that routes low pressure fluid back to the pump reservoir. High pressure supply hoses are made from a reinforced material capable of withstanding high operating pressures (up to 1,300 psi) and high temperatures (250 to 300° F). Return hoses, on the other hand, operate at much lower pressures (usually less than 50 psi). If a hose needs to be replaced, use the correct type for the application.
Sometimes rubber power steering hoses deteriorate internally. Small pieces of rubber flake loose and lodge in the valves within the pump or steering gear. This can cause the pump to work harder in an attempt to overcome the blockage, resulting in increased noise and steering effort. Old hoses should be replaced to prevent expensive pump and/or steering gear damage.
When hoses, the rack or power steering pump are replaced, the entire system should always be flushed to remove all the old dirty fluid. Power steering fluid deteriorates over time, and accumulates contaminants that can damage newly installed parts. As the fluid ages, its viscosity increases, which can increase steering effort when the fluid is cold. The fluid can also leave varnish deposits that can affect the operation of the pump and spool valves in the rack.
Some experts recommend changing the power steering fluid every 50,000 miles for preventive maintenance. This type of service can prolong the life of the power steering pump and rack as well as the internal seals.
Always use the type of power steering fluid specified by the vehicle manufacturer since fluid requirements vary from one vehicle to another. Using the wrong type of fluid may cause seal swelling and leakage and may void the warranty on a new or reman replacement rack.
OTHER RACK PROBLEMS
Of course, leaks aren't the only problem that can afflict a steering rack. As the miles add up, the constant pounding, vibration and friction wears the inner tie rod sockets and increases play between the rack and pinion gears. Worn tie rod sockets will have the same effect as worn tie rod ends, creating play in the steering and causing a change in toe alignment that will accelerate tire wear.
Inner toe rod wear can also be checked by placing the wheels on the ground and having an assistant rock the steering back and forth while you look and feel for looseness in the linkage and sockets. With soft rubber bellows, you can pinch the bellows to feel the tie rod sockets inside. But with hard plastic bellows, you'll have to slide the bellows back to see the sockets.
Center wear is another common problem that can afflict a high-mileage rack. Steering wears most in the straight ahead position because that's the direction of travel most of the time. Wear between the pinion gear and rack teeth creates looseness that may contribute to steering wander and increased feedback (noise or harshness when hitting bumps, for example).
Most racks have a pinion preload adjustment. But if the adjustment is made with the rack in the centered, straight ahead position, it may cause the rack to bind when the steering is turned to either side. If you attempt to make an adjustment to compensate for wear, therefore, make sure the rack is steered to one side before tightening the adjustment nut. Also, make sure the steering turns lock to lock without binding after the adjustment has been made.
If the steering feels loose, you should also inspect the outer tie rod ends, steering input shaft coupling, rack mounts and front wheel bearings before adjusting or replacing anything.
Some power steering systems are inherently noisy and there isn't much you can do about it. A certain amount of hissing during normal low speed maneuvers is normal. But unusual noise usually means trouble.
The familiar high-pitched squeal or chirping that occurs when the steering wheel is cranked to one side or the other usually indicates a loose or oil-soaked belt. Check belt tension, and the automatic tensioner if the engine has a serpentine belt.
If the belt is soaked with oil, no amount of tightening will restore its grip. But don't just replace the belt and consider the problem fixed. You also need to fix the oil leak, otherwise the replacement belt will suffer the same fate.
Buzzing noises are usually caused by a bad control valve in the pump. Replacing the valve may be all that's necessary to eliminate the problem. But if the pump itself is whining, the pump shaft bearings are shot and it's time to replace the pump.
Groaning noises can be caused by restrictions, low fluid level or air in the system.
Rattling usually indicates mechanical vibration. Check the pump mounting brackets on the engine, and for contact between the pressure hose and the chassis or other parts.
A growl may be the result of a restriction in the steering gear or hose, or the result of pump cam ring wear or a scarred pump pressure plate, thrust plate or rotor.
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