What Is Rack and Pinion Steering?- A Full Guide

What is a rack and pinion steering?

A rack and pinion steering system consist of a pinion (a circular gear) with a rack (a linear gear). The system works by converting rotary motion into linear motion. Most cars, small trucks, and SUVs are equipped with a rack and pinion steering system and not the recirculating ball steering found in larger trucks, larger SUVs, and other heavy-duty vehicles.

With rack and pinion steering, rotation of the pinion causes linear movement of the rack, turning the vehicle’s wheels left or right. Rack and pinion systems are common components on railways. In between train rails are racks that interact with pinions attached to locomotives and train cars to assist trains with moving up steep inclines.

While a rack and pinion system may seem complicated, it is simply a gear attached to a toothed bar. The bar attaches to a set of tie rods. A generating rack is a rack outline used in the design of a generating tool such as a hob or a gear shaper cutter to indicate the details and dimensions of the teeth.

Simple linear drives often consist of a combination of rack and pinion. Pinion shaft rotation is driven by hand or motor to produce linear motion.

While the rack and pinion steering system has been used by US automakers for less than 50 years, in other countries the concept is almost a century old.

Related Article: What is Steering System?

rack and pinion steering

How do rack and pinion steering work?

Rack and pinion steering use a gear set to convert the circular motion of the steering wheel into the linear motion required to turn the wheels. It also offers a gear reduction so turning the wheels is easier.

It works by enclosing the rack and pinion gear 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 you turn the steering wheel, the gear rotates and the rack moves. The axial rod at each end of the steering 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 takes off: bolts attach the tie rods to the center of the steering rack.

How does rack and pinion steering work with power steering?

When a rack and pinion system is connected to a power steering system, the design changes slightly. A cylinder with a piston in the middle is placed on the rack. There is fluid on both sides of the piston. When pressure is applied to the fluid on one side of the piston, it forces the piston to move, which rotates the steering rack and assists with steering.

rack and pinion power steering

Common rack and pinion steering problems

There are a few ways you can tell if your steering gear is failing, such as excess noise, movement, effort, or leaks.

When you’re turning the steering wheel and it seems to be looser or tighter than the rest of the rack, you could have a flat spot or notch in the steering. Wandering might be associated with this spot, usually when the wheels are pointed straight ahead.

This usually indicates a worn spot in the rack teeth, which will require replacement, such as with this remanufactured power steering rack and pinion unit.

Excessive steering effort usually indicates a fault in the power booster. To fix this, check and adjust the power steering oil level and check for abnormal noises in the power steering pump. Aside from pump issues, internal leaks can cause excessive effort when steering left or right.

External fluid leaks are another common problem with the rack and pinion hydraulic steering systems. The power assist area of ​​the steering box is rather small, but there are several seals that keep the fluid in the system.

Unfortunately, these seals are so inaccessible that many repair shops simply choose to install a refurbished replacement unit when treating the leak. Also, fluid leaks can cause excessive steering effort and damage to the power steering pump, adding significantly to the complexity of the repair.

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.

These 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 does a rack and pinion leak happen?

It is possible that one of the hoses or lines in your power steering system can begin to leak either at the connection or due to the flexible rubber section cracking. However, it is more likely that your power steering system will develop a leak at one of the seals on your rack and pinion.

There is a seal where your steering column enters the rack and pinion assembly, then a seal where each tie-rod attaches. Each of these seals has to keep high-pressure power steering fluid contained while allowing the steering column to rotate and the tie rods to move as well. Over time these seals can dry out, shrink, crack or become unseated causing a leak.

How to find a rack and pinion leak?

To find your rack and pinion leak you can check these three seals relatively easily. The only difficult part is fitting underneath your vehicle but if you have ramps or jack and jack stands that can be easily accomplished, just make sure your vehicle is secure before you crawl under! 

The rack and pinion should be one of the lowest components on your vehicle and will likely be just under your engine’s oil pan.

Why are rack and pinion leaks expensive to fix?

The reason rack and pinion leaks are so expensive to fix are that the seals are often not serviceable, even by a mechanic. Most rack and pinion leaks will require the replacement of the entire rack and pinion assembly even if most of it works just fine.

The good news is you do have another alternative to an expensive replacement. You can simply and quickly restore the seals in your rack and pinion without ever removing them.

Adding Blue Devil Power Steering Stop Leak to your power steering reservoir today will start to seal your power steering leaks immediately and is guaranteed to permanently seal your rack and pinion leak within a few days of driving.

Blue Devil Power Steering Stop Leak is specially formulated to revitalize and restore the seals in your power steering rack returning them to their original size and function to seal your leak. Blue Devil Power Steering Stop Leak will not harm or clog your rack and pinion and is safe to remain in your system until your next scheduled power steering flush.