Rack and Pinion Steering: Working, leak, and Replace

What is rack and pinion?

A rack and pinion is a type of linear drive that includes a circular gear (the pinion) that meshes with a linear gear (the rack) and converts rotary motion into linear motion. When the pinion is rotated, the rack is driven linearly. When you drive the rack linearly, the pinion is driven into rotation.

A rack and pinion drive can use both straight and helical gears. Helical gears are preferred because of their quieter operation and higher load capacity.

The maximum force that can be transmitted in a rack and pinion mechanism is determined by the tooth pitch and the size of the pinion.

For example, in a rack railway, the rotation of a pinion mounted on a locomotive or railroad car engages a rack between the rails and helps move the train up a steep incline.

There is a base rack for every pair of conjugate involute profiles. This base rack is the profile of the conjugate gear with an infinite pitch radius. A generation rack is a rack outline used to indicate tooth details and dimensions for the construction of a generation tool, such as a hob or gear mill.

While there are several types of steering systems used on the market, the two main ones are recirculating ball steering, which is mostly used for heavy vehicles, trucks, and larger SUVs, and rack and pinion steering, which is commonly found on cars, small trucks and SUVs.

What is a rack and pinion steering?

Rack and pinion steering is quickly becoming the most common type of steering in cars, small trucks, and SUVs. It’s actually a pretty straightforward mechanism. A rack and pinion set is enclosed in a metal tube with each end of the rack protruding from the tube. A rod called a tie rod is attached to each end of the rack.

The pinion gear is attached to the steering shaft. When you turn the steering wheel, the gear rotates and moves the rack. The tie rod at each end of the rack is connected to the steering arm on the spindle (see diagram above).

The rack-and-pinion gearset does two things:

  • It converts the rotational motion of the steering wheel into the linear motion required to turn the wheels.
  • It provides a gear reduction, making it easier to turn the wheels.

On most cars, it takes three to four full turns of the steering wheel for the wheels to turn from lock to lock (left to right).

rack and pinion steering

How does rack and pinion steering work?

A rack and pinion steering works by using a gear system to translate the steering wheel’s circular motion into the linear motion needed to turn the wheels. The pinion gear connects to the steering shaft so that the gear will spin and move the rack when the steering wheel turns.

It also provides a gear reduction, so turning the wheels is easier.

It works by enclosing the rack and pinion gear-set in a metal tube with each end of the rack protruding from the tube and connected to an axial rod. The pinion is attached to the steering shaft so that when the steering wheel is turned, the gear rotates and the rack moves. The axial rod at each end of the rack is connected to the tie rod end which is attached to the spindle.

The rack and pinion gear set has two main functions:

  • Conversion of the steering wheel’s rotational motion into the linear motion needed for the vehicle’s wheels to turn
  • Reduction of gears, which makes it easier for the steering wheel to turn the wheels

Rack and pinion steering ratios

A Steering ratio is defined as the ratio of how far the steering wheel turns to how much the wheels turn. For example, if a 360-degree turn of the steering wheel causes a car’s wheels to turn 20 degrees, then that car’s steering ratio is 18:1 (360 divided by 20).

A higher steering ratio requires more turns of the steering wheel to turn the wheels. A lower steering ratio is desirable as it indicates more responsive steering.

Light sports cars tend to have a lower steering ratio compared to large cars and trucks. Thanks to the power steering, all consumer vehicles have an improved steering ratio.

There are two main types of rack and pinion steering systems:

  • End take off: the tie rods are attached to the end of the steering rack via the inner axial rods.
  • Centre take off: bolts attach the tie rods to the centre of the steering rack.

What is rack and pinion power steering?

Rack and pinion steering uses a gear-set to convert the circular motion of the steering wheel into the linear motion required to turn the wheels. The pinion gear is attached to the steering shaft so that when the steering wheel is turned, the gear spins, moving the rack.

When a rack and pinion system is connected to a power steering system, the design changes slightly. A cylinder with a piston in the center is inserted into the rack. There is liquid on both sides of the piston. When pressure is applied to the fluid on one side of the piston, the piston is forced to move, rotating the rack and assisting steering

Power steering vehicles have slightly different rack and pinion designs. On the side of a power rack there are two steel tubes that perform the function of turning left and right and at the same time serve as pressure and return lines.

A cylinder containing a piston with two fluid ports is connected to the rack. High-pressure fluid moves the piston, causing the rack to move. Electrical systems use an electric pump

rack and pinion power steering

Application of rack and pinion

A rack and pinion with two racks and one pinion is used in actuators. An example is pneumatic rack and pinion actuators that can be used to control valves in pipeline transport. The actuators in the picture on the right are used to control the valves of large water pipeline.

Here are a few more applications of reck and pinion:

  • Car steering: In many types of vehicles, the steering shaft attached to the vehicle wheel is connected to a small pinion. When the wheel is rotated, the gear rotates and the rack and pinion gear set translates the rotary motion into linear motion. From here a tie rod at the end of the rack is connected to the steering arm to ensure that the linear movement is being sent in the correct direction.
  • Railways: Problems often arise when trains and other locomotives have to travel up a steep slope. But a rack and pinion can help here – a rack is placed along the hill and pinions provide the force needed to propel the machine up the hill.
  • Stairlifts: Virtually all stairlifts contain a rack and pinion gear, the gear wheel allowing upward movement in a manner similar to that above.
  • Actuators: Actuators are machines that move various components, such as a pipeline transport system. In such a system, a rack and pinion gear helps to control the valves that the system needs for its basic function.

Common rack and pinion steering problems

Some rack and pinion systems will wear out over time. Another common rack and pinion steering problem is that the bushings and bearings might wear out, leading to excessive slipping and a loose feeling in the steering wheel when driving. If there is a leak within the system, power steering fluid can slowly drain out.

Here are some symptoms or warning signs to alert you to a potential problem with your Stearing rack:

  • Very tight steering wheel
  • Leaking power steering fluid
  • Grinding noise when steering
  • Burning oil smell

1. Very tight steering wheel

Today’s rack and pinion steering systems are supported by power steering that uses hydraulic pressure to allow easy and quick handling of the steering wheel. If the steering wheel feels tight or is harder to turn than usual, it is usually because the rack or transmission is generating more heat, or the hydraulic pressure from the power steering is decreasing.

Either way, it is a problem that cannot be fixed and should be checked by a mechanic as soon as possible. Sometimes it’s as simple as adding more power steering fluid or making a minor adjustment that can solve this problem and extend the life of your steering rack.

2. Leaking power steering fluid

As noted above, sometimes tight steering is indicated by low power steering fluid. However, since the steering box is hydraulically powered, the fluid levels won’t decrease unless there is a leak somewhere in the system.

Once you start leaking power steering fluid, it means that a loose fitting, broken seal, or other mechanical problem is causing the leak that needs to be fixed as soon as possible. Otherwise, the rack or gearbox will develop excessive heat and possibly break gears and other components, which could result in a crash.

Leaking steering fluid can be distinguished from other fluids by its smell (typically a burning oil smell). It is also usually red or pink in color and drips from the back of your engine. If you discover this type of fluid under your car, contact a mechanic as soon as possible to investigate and repair the leak before the leak causes additional damage.

3. Grinding noise when steering

A bad or defective gearbox is usually caused by a lack of lubrication and maintenance. The excess heat creates metal-to-metal contact and therefore creates a loud grinding noise when you turn left or right. You can really notice this sound if you turn and hit a bump at the same time, such as driving into a driveway.

If you notice this crunch while steering left or right, contact a mechanic so they can quickly diagnose the steering gear and replace it if necessary.

4. Burning oil smell

A less common warning sign of a damaged rack or gearbox is the smell of burning oil. Since the power steering fluid itself smells like burnt oil, the strong smell of burnt oil is present when the steering gear is hot.

If this happens, stop your vehicle immediately, find a safe parking space, and call a mechanic as soon as possible. Continuing to drive while a steering gear overheats can result in fire and catastrophic damage.

How to Repair a Rack and Pinion Leak?

Rack and pinion leaks are often expensive to fix as the seals are difficult to service, even by a mechanic. Most leaks are solved by replacing the entire rack and pinion system to ensure the system works correctly. An alternative is a “power steering stop leak” product.

Rack and pinion leaks can be frustrating and difficult to understand why mechanics charge so much money to fix them. A rack and pinion steering systems are often used in sports cars and other vehicles that are close to the ground or have little space in front of the vehicle.

This systems are more commonly used in these situations because they are relatively compact systems and do not require complex connections like the steering gear systems of most trucks.

What happens when rack and pinion failed?

It is important to know what happens when the rack and pinion run out. When a pinion is about to fail, steering can be very difficult. However, if a rack or pinion fails, you lose complete control of the steering.

It is extremely dangerous for a rack or pinion to run out because the power steering system in your vehicle uses the power steering pump to pressurize the power steering fluid and deliver it to your rack and pinion.

This high pressure fluid helps the rack move when the steering wheel is turned so it won’t be that difficult for you to turn the wheels when your vehicle is moving slowly or when your vehicle is stopping. Like any high pressure hydraulic system, the power steering system used with the rack and pinion can leak.

How does a rack and pinion leak happen?

It is possible that one of the hoses or lines in your power steering system is starting to leak either at the joint or because of cracks in the flexible rubber area. However, it is more likely that your power steering system will develop a leak from one of the seals on the rack and pinion.

There is a seal where your steering column enters the rack assembly and a seal where each tie rod is attached. Each of these seals must contain the high pressure power steering fluid while the steering column can rotate and the tie rods can also move. Over time, these seals can dry out, shrink, crack, or loosen and cause a leak.

How to find a rack and pinion leak?

To find your rack leak, you can check these three seals with relative ease. The only difficult part is installing it under your vehicle. However, if you have ramps or a jack that is easy to get to, just make sure your vehicle is safe before crawling under! The rack and pinion should be one of the lowest components of your vehicle and will likely be right under your engine’s oil pan.

How to fix a rack and pinion leak?

Most leaks are solved by replacing the entire rack and pinion system to ensure the system works correctly.

An alternative is a “power steering stop leak” product. While these might look like a good solution, they are only a temporary fix and will remain in your power steering system until your next power steering flush.

How to Replace a Power Steering Rack and Pinion?

Feel you’re up to it? Are you ready to get started? Then let’s do it!

  1. Put the wheels in a straight-ahead position. The steering wheel should be in the center position. Remove the key from the ignition and make sure the steering wheel is locked. You do not want the steering wheel to turn while removing the rack. Doing so will make it possible for the spiral cable in the steering wheel to unwind and become useless.
  2. Crack loose all the wheel lug nuts
  3. Raise and support the vehicle with approved jack stands.
  4. Remove both front wheels.
  5. Remove the Steering Shaft Coupler Outer Seal and unbolt the upper pinch bolt on the Steering Shaft Coupler assembly.
  6. Detach the outer tie rod ends. You may need to use a special tie rod end puller to get them off. You can rent one at the local rental store. Most times a sharp rap with a BFH on the end of the tie rod mount will shock it loose. Do not hit the tie rod end itself.
  7. Remove any parts required to gain access to the rack mounting bolts, lines, and steering coupling.
  8. Depending on accessibility, at this point, you can remove the power steering rack mounting bolts, or crack the power steering high pressure and return lines.
  9. Depending on accessibility, at this point, you can remove the power steering rack mounting bolts, or crack the power steering high pressure and return lines. It may be easier to get a wrench to swing on a power steering line fitting once you’ve unbolted the rack and moved it a bit. Also, reattaching the lines may be easier before the new rack is bolted in place.
  10. Place a drain pan under the vehicle and remove the hydraulic power steering pressure hose and power steering return hose from the power steering rack.
  11. Now comes the fun part, twist and turn and jiggle it out through one of the wheel well openings. Make sure the kids are in the house because certain words will be necessary to coax the rack out and they are not words little ears should hear.
  12. If the new rack has new tie rod ends, measure the overall length of the old rack and tie rod assembly. Set the overall length of the new assembly to this same dimension by twisting the tie rod ends on their threads. Keep the rack centered and split the overlap difference between the left and right rod ends as you do this, or the steering wheel will be off-center when you’re done.
  13. If you are reusing the old tie rod ends, crack the lock nuts loose. Count how many full turns it takes to remove the tie rod ends. Center the new rack and install tie rod ends the same number of turns on the new rack. Again, check the overall length and split the difference.
  14. Install the new rack using the same words you used to get it out.
  15. Reconnect the power steering lines, using new “O” rings, if required. Usually, the high-pressure line uses a slightly larger “O” ring so be careful not to mix them up.
  16. Reconnect the Steering Shaft Coupler assembly and bolt the rack back into place.
  17. Reattach the tie rod ends to the steering knuckles. Use new cotter pins for the castellated nuts; never reuse the old cotter pins.
  18. Put the wheels back on and torque the lug nuts to specifications.
  19. Remove the return line from the power steering pump and place the end into a bucket.
  20. Fill the power steering pump and start the engine until clean fluid comes out of the return hose. You may be able to install an inline filter in the return line to protect the new rack. I have known guys who have used fuel filters for this purpose.
  21. Has the front end aligned to reset the toe-in adjustment to specification or the vehicle will handle poorly and wear out the tire quickly?

FAQ

What is a rack and pinion?

A rack and pinion is a type of linear drive that includes a circular gear (the pinion) that meshes with a linear gear (the rack) and converts rotary motion into linear motion. When the pinion is rotated, the rack is driven linearly. When you drive the rack linearly, the pinion is driven into rotation.

What is rack and pinion steering?

Rack and pinion steering is quickly becoming the most common type of steering in cars, small trucks, and SUVs. It’s actually a pretty straightforward mechanism. A rack and pinion set is enclosed in a metal tube with each end of the rack protruding from the tube. A rod called a tie rod is attached to each end of the rack.

What is rack and pinion leak?

Rack and pinion leaks are often expensive to fix as the seals are difficult to service, even by a mechanic. Most leaks are solved by replacing the entire rack and pinion system to ensure the system works correctly. An alternative is a “power steering stop leak” product.

How to Replace a Power Steering Rack and Pinion?

Break all the lug nuts free before using the jack. Lift the car and support it safely on stands. Then, unbolt the clamp that connects the steering column to the pinion shaft. Detach the outer tie rod ends.

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