Would you believe the first primitive rack & pinion steering gear made its automotive debut in a three wheeled motorized tricycle back in 1896? In those days, it was called a “Worm & Sector” steering gear. Though crude by today’s standards, it was better than using a tiller to steer the front wheels.

The early steering gears required a lot of effort, so steering wheels had to be large. In the 1920s, cam and roller gear steering systems provided reduced steering effort and better road feel.

The next major innovation in steering technology was “Recirculating Ball” steer-ing. In this design, steel balls are used to reduce friction inside the steering gear. The balls ride in grooves on the steering shaft. When the shaft turns, the balls slide a large nut back and forth to rotate the pitman arm

sector gear. The pitman arm is connected to the steering linkage and steers the wheels right or left depending on the direction it rotates.

Recirculating ball steering gears reduce steering effort and are often used on larger, heavier vehicles. This type of steering gear is still used today,

especially in many pickup trucks. But in the 1960s, rack & pinion steering began its comeback, first in Europe, and then in

the U.S. when front-wheel drive (FWD) became all the rage in the 1980s. Today, rack & pinion steering is used on most passenger cars, SUVs and minivans.

THE ADVANTAGES OF THE RACKThe main advantage of the rack is its simple design that makes it less expen-sive to manufacture than a recirculating ball steering gear. It’s also lightweight, quick acting and provides better road feel and feedback than a recirculating ball steering system.

A rack & pinion steering system has a spiral cut pinion gear on the end of the steering input shaft. The pinion gear turns against teeth cut into a horizontal steel bar that slides back and forth (the “rack”). The

two components are located in a cast alumi-num housing, with bearings supporting the pinion shaft and bushings supporting the rack.

Mounted on both ends of the rack are inner tie rod sockets. These are attached to the tie rods and outer tie rod ends that connect to the steering arms on both wheels. Rubber or plas-tic bellows on the ends of the rack surround and protect the inner tie rod sockets.

POWER STEERINGManual racks are fairly rare these days, so most racks are power assisted. A hydraulic power steering system uses a belt-driven pump to generate hydraulic pressure, which is routed through hoses to the steering gear to provide power assist. A torque sensor in the steering column or the steering gear works in

• Advantages of the Rack• Power Steering• Steering Rack Problems• Symptoms That May Indicate Rack Trouble

• Rack Inspection• Rebuild or Replace?• Replacement Racks• Rack Installation Tips

ISSUE 12.2009

©2009 National Automotive Parts Association

Rack & Pinion Steering

The basic concept of rack & pinion steering goes way back. Turning the steering wheel rotates a pinion gear

on the end of the steering shaft. The gear moves the rack sideways to steer the wheels.

Recirculating ball steering is still used in many trucks, but has a more com-

plicated steering linkage than rack & pinion steering requires.

Continued on next page

conjunction with a control valve assembly to direct hydraulic pres-sure to the rack.

Inside the rack housing is a hydraulic cylinder that surrounds the rack. A piston seal on the rack divides the cylinder into two chambers. When pressure is routed into one chamber, it pushes the rack in the opposite direction to provide power assist.

Operating pressures within a power rack generally do not exceed 100 PSI when the wheels are in the straight-ahead position. In an easy turn, the pres-sure can increase to as much as 300 PSI, and up to 700 PSI in a tight turn or when parking.

Many power racks incorporate “variable rate” power assist. The effort required to steer the wheels changes with the vehicle’s speed or how quickly the driver is turning the steering wheel. Maximum power assist is usually provided at low speeds when extra muscle is needed for parking maneuvers. At higher speeds, the amount of assist is reduced by venting pressure via a control valve on the rack to improve road feel and steering stability.

The latest generation of power racks are now using an electric motor instead of a pump and hydraulic pressure to provide power assist. Electric Power Steering (EPS) eliminates the need for a power-robbing and noisy PS pump and leak-prone hoses. EPS also allows greater refinement and variability in steering assist since it can be tied into an Electronic

Stability Control (ESC) system. You’ll find electric power racks on many late model applications such as Chevy Malibu, Cobalt, Equinox and HHR, Pon-tiac G5, G6 & Torrent, and Saturn ION and VUE.

STEERING RACK PROBLEMSThough steering racks are engineered to last the life of the vehicle, how long they actually last depends on miles driven, the type of driving (urban driving with lots of sharp turning versus highway driving with few-er and more gradual turning), road conditions (rough roads versus smooth roads), environmental factors (heat, cold, moisture, road salt, dirt, etc.) and age.

No rack lasts forever. They all eventually wear out. The greatest wear between the pinion and rack teeth occurs in the straight ahead position (center wear) because the rack is in this position most of the time while the vehicle is being driven. Center wear or wear in bushings that maintain lash between the rack & pinion can result in steering play and looseness.

The rack bushings and seals also experience wear from the sliding action of the rack itself. This can lead to leaks in power racks that allow fluid to es-cape into the bellows. More than an ounce of fluid inside the bellows means the seals are leaking.

Another common wear item are the spool valve seals in the pinion housing. Leaks here can result in a loss of power assist that is usually most noticeable when the vehicle is first started on a cold morning.

The pounding and vibration that transmits through the steering linkage from normal driving can also wear out the inner tie rod sockets and outer tie rod ends. This can cause steering looseness and wan-der, as well as rapid toe wear on the front tires.

The protective rubber or plastic bellows on the ends of the rack may also crack or leak from age or exposure to extreme cold. This can allow outside contaminants to get at the inner tie rods ends and rack seals, accelerating wear.

The rubber mounts that support the rack hous-ing can deteriorate over time, allowing the rack to move. This may cause steering noise or wander.

The effort required to steer the wheels changes with the vehicle’s speed or how quickly the driver is turning the steering wheel.

Power Rack

Basic components in a rack & pinion steering system.

Rack & Pinion Steering

SYMPTOMS THAT MAY INDICATE RACK TROUBLEAny of the following symptoms could indicate possible rack trouble, and should be investigated to determine the cause:

Steering noise (clunks, rattles, pump •noise, etc.)

Loose steering or play in the •steering wheel

Erratic steering (wandering)•

Steering pull to either side•

Harsh steering (excessive feedback •through the wheel)

Slow steering return•

Increased steering effort or loss of •power assist

Power steering fluid loss or leaks•

Steering jerk over bumps•

RACK INSPECTIONA simple undercar check should look for the following:

Presence of fluid in the rack bellows •(indicates internal leakage which requires rack replacement).

Damaged rack bellows (replace if bad)•

Looseness in inner tie rod sockets -- •

Check by rocking the steering back and forth with the weight of the vehicle on its wheels. There should be no play.

Movement between rack and chassis •when steering is rocked.

Excessive play in steering wheel (should •be less than 1/4 inch)

Steering bind (could be due to corroded •steering input shaft U-joint coupling, misadjusted rack yoke or rack damage, or bad upper strut mounts).

Fluid leakage around steering input •shaft (can sometimes be fixed with an input shaft seal kit but may require rack replacement).

Fluid leakage around power steering •hose connections (replace hose seals as needed).

Squareness of rack with respect to •chassis & road (if rack is not parallel to the steering axis, it can cause uneven toe changes during suspension jounce/rebound resulting in “bump-steer” condition).

REBUILD OR REPLACE?Few technicians rebuild racks because most high mileage racks need a lot more than a seal kit. The bushings and spool valve housing are often worn, as are the rack cylinder, and rack and pinion gear teeth.

Minor problems such as worn inner tie rod sockets, split or torn bellows, or deterio-rated or loose rack mounts can be repaired without having to replace the rack. But any problems that affect the rack itself usually require replacing the rack with a new or remanufactured unit.

REPLACEMENT RACKSNAPA has a full line of both new and re-manufactured Rack & Pinion steering gears to fit most domestic and import applications.

Replacement racks are available in two basic types: short racks and long racks. If the original inner tie rod sockets are still in good condition and can be reused, a short rack can save your customer some money. But if the inner tie rod sockets have a lot of miles on them or are worn out, you’ll have to go with a long rack that comes complete with the tie rods and bellows already mounted.

RACK INSTALLATION TIPSBefore installing a new or remanufac-tured rack, drain and flush out the power steering pump and lines to remove all traces of the old fluid. Flushing is a must because contaminants in the old fluid can ruin a replacement rack.

Center the steering wheel and center the rack before reconnecting the tie rod ends and steering shaft coupling. Toe alignment will have to be checked and adjusted after the rack has been installed.

When installing the pressure lines on a power rack, be careful not to over-tighten

the fittings. Follow the manufacturer’s torque recommendations and be careful not to cross-thread fittings that screw into the aluminum housing (doing so may void the rack’s warranty).

ISSUE 12.2009

Places where a steering rack may leak fluid.

Some of the things that need to be inspected on a rack & pinion steering system.

Continued on next page

Most only call for 10 to 15 ft. lbs. of torque (use an accurate torque wrench).

Refill the power steering pump reservoir with the type of fluid specified by the vehicle manufacturer. Some allow Dexron ATF to be used, but many specify a particular type of PS fluid that contains special additives for the pump and steering gear. Using the wrong fluid can cause problems later.

After the PS pump has been filled with fresh fluid, the system must be purged of air. This can be done by raising the front of the vehicle so the wheels are off the ground, and SLOWLY cycling the steering back and forth lock-to-lock 20 to 30 times. Continue until no air bubbles can be seen in the fluid. Add fluid as needed to top off the reservoir, then start the engine and cycle the steering again 10 to 20 times. If the steering is noisy or there are bubbles in the fluid, shut the engine off and repeat the purging procedure again.

Related items that should also be inspected and may need to be replaced include the rack mounts, the steering input shaft coupling, the PS pump belt and hoses. You should also inspect the upper strut bearing plates on vehicles with MacPherson strut suspensions as wear here can also cause steering noise, binding or increased steering effort.

To check the strut bearings, turn each wheel side-to-side while the tie rod ends are disconnected from the steering arms. Any binding or stiffness usually means the strut bearings need to be replaced (it’s a good idea to replace both even if only one is binding). Rarely do the lower ball joints cause problems in these applications because the ball joints don’t carry any weight. The load is carried by the strut bearings.

•The rack gear on a rack and pinion steering unit should always be held with a wrench when removing an inner socket as-sembly. Failure to hold the rack gear may cause the seals in the unit to fail because of the unusual twisting that will occur between the rack teeth and the pinion.

• If the steering rack is not horizontal, the amount of toe on the left and right will be different. This can create a bump-steer condition. If you are trying to diagnose a bump-steer condi-tion, measure the distance from both ends of the rack to the ground. They should be the same. It’s not unusual for the rack mounting brackets to get loose or even fracture from road shock, throwing the rack out of alignment.

•Many European vehicles use mineral oil based power steering fluid. Mineral oil based fluid has a green tint, and most P/S reservoirs are tagged for oil identification. Mineral oil based fluids should never be mixed with other types of power steering fluid. Mineral oil systems use different types of seals that can be damaged by petroleum based fluids. There are other types of special power steering fluids specified for vehicles that go far beyond Dexron ATF of years past. Always use the correct type of fluid specified for each vehicle.

•Whenever a rack and pinion steering gear is changed, when hoses are replaced, or when a power steering pump is installed, the entire power steering system should be flushed and refilled with clean fluid. After filling, the system should be bled accord-ing to the manufacturer’s recommended procedure.

TECH tips

Review Questions

Get more Autotech technician training by calling 800-292-6428 or by visiting us on the web at www.napaautotech.com

QUESTIONSQuestions about the products featured in this issue of the Tech’s Edge? Contact your NAPA AUTO PARTS Store Representative.

Answers: 1. c, 2. d, 3. b

Operating pressures within a power rack when parking can increase to: a. As much as 300 PSIb. As much as 500 PSI c. As much as 700 PSI d. As much as 900 PSI

A common wear point in a steering rack is: a. Center wear at the gear rack b. Rack bushings and seals c. Spool valve seals d. All of the above

Before installing a new or remanufac-tured rack, what must be done?a. Align the front wheels b. Drain and flush out all the old fluid c. Replace the P/S belt d. Test the operating pressure

NAPA replacement racks are available for most import and domestic vehicles.