The Ultimate Wheel Cylinder Guide: Function, Symptoms, FAQs

The wheel cylinder plays a significant role in your car’s drum brake system.

Its job is to apply the brake shoes onto your brake drums, which slows down your car.

But what exactly is the wheel cylinder?
What are the things that can go wrong with it?

In this article, we’ll dive into all the ins and outs of the wheel cylinder, cover some common problems with it, and answer some wheel cylinder FAQs.

This Article Contains

What Is a Wheel Cylinder?
The Anatomy of a Drum Brake Wheel Cylinder
How Does the Wheel Cylinder Work?
What Are the Symptoms of a Faulty Wheel Cylinder?
Why Does the Wheel Cylinder Fail?
7 Wheel Cylinder FAQs

Let’s begin.

What Is a Wheel Cylinder?

The brake wheel cylinder is a crucial component of your car’s drum brake system.

The wheel cylinder is positioned at the top of the wheel inside the drum brake — fixed to the drum brake backing plate with mounting bolts. The backing plate protects the brake wheel cylinder components from water, dirt, and debris.

Also called a slave cylinder, it applies force on the brake shoes to help halt a car. Like any moving component, the slave cylinder is subject wear and may become damaged, which leads to a brake fluid leak and hindered brake performance.

What is it used for in the brakes?
It’s used to push a pair of brake shoes outwards so that they can contact a brake drum to slow down your vehicle with friction.

How is this different from a disc brake?
Unlike the drum brake wheel cylinder that delivers a pushing force onto a brake shoe, a disc brake caliper squeezes brake pads onto a spinning rotor to slow the car down.

How standard are drum brakes?
While most modern vehicles use disc brakes, it’s still common for older vehicles or small trucks to have drum brakes on their rear tires.

Now that we’ve covered the basics, let’s dive deep into how wheel cylinders are structured. It’ll make it easier for you to understand how things can go wrong later.

The Anatomy of a Drum Brake Wheel Cylinder

The wheel cylinder structure is relatively simple.

Its main body is a cylinder with a bore, typically made of cast iron or aluminium. The iron or aluminium protects it from corrosion and rust.

A new wheel cylinder bore is fitted with these:

A piston on each end that connects to a brake shoe via a shaft.
Each piston has an internal piston seal (or rubber cup) to maintain brake pressure and prevent brake fluid from leaking past the piston.
A spring between the pistons that hold each piston seal in position.
An outer dust boot (also called a dust cap) covers each end of the wheel cylinder. The dust cap protects the cylinder bore from moisture, brake dust, and dirt.

In addition to those, there are two other vital components:

An inlet port that connects the wheel cylinder to a brake line that carries brake fluid.
A bleeder screw that’s used to bleed brake fluid and eliminate air from the brake cylinder. The bleeder screw is hollow, with a small hole in the head that assists with brake bleed.

Now that we understand the structure of a brake wheel cylinder, let’s get to how the wheel cylinder functions with the rest of the braking system.

How Does the Wheel Cylinder Work?

When you depress the brake pedal, the force generated by your foot transfers to the brake master cylinder.

The master cylinder then converts this force into hydraulic pressure, carried by brake fluid through a brake line to each wheel cylinder.

This pressurized brake fluid in the wheel cylinder then pushes the cylinder pistons outwards, pressing each brake shoe against the rotating brake drum to stop the wheel.

When the brake pedal is released, return springs pull the brake shoes away from the brake drum, pushing each wheel cylinder piston back into their bore.

FYI: This dual piston design isn’t the only type of wheel cylinder. Some drum brake configurations use a pair of single piston wheel cylinder components — one at the top of the drum and one at the bottom, each connected to a brake shoe.

Let’s find how to tell if your wheel cylinder is failing.

What Are the Symptoms of a Faulty Wheel Cylinder?

A bad wheel cylinder is often hard to spot because it’s inside the drum brake.

However, here are some signs that something’s wrong with it:

Your car has poor brake response — you’ll find that braking takes longer
Your brake pedal feels mushy, soft, or the pedal sinks to the vehicle floor
There’s a brake fluid leak in your rear brake drum that pools near a rear wheel
The rear drum brakes drag or lock up

If you run into any of these problems, don’t drive your car.
Driving with faulty brakes can be dangerous, so get a mechanic to come to you or visit a repair shop for assistance.

With that being said, what causes a faulty brake wheel cylinder?

Why Does the Wheel Cylinder Fail?

Since a wheel cylinder contains so many moving parts, this hard-working component can fail for many reasons.

Here are five of the most common ones:

1. Rubber Seal Failure

The wheel cylinder piston seal and dust boot are made of rubber.

These seals become brittle with time and can fail with exposure to extreme heat or due to natural wear and tear.

When they fail, your vehicle may have a brake fluid leak, and the hydraulic pressure will drop in the braking system, compromising your braking performance.

2. Worn Pistons

Pistons are meant to be a specific diameter relative to your cylinder bore size.

However, with time, pistons can wear down and won’t fit snugly in the cylinder bore anymore. If this happens, there’s a risk of a piston seal leaking or the piston rocking, which can increase wear.

3. Stuck Pistons

The cylinder bore is supposed to have a smooth surface.

However, corrosion and pitting can develop in the cylinder bore due to exposure to moisture in the brake fluid, which can cause your piston to get stuck.

Stuck pistons result in a drum brake that won’t release, creating major braking problems in your drum brake system.

4. Pistons that Slip Out of the Bore

Excessive brake drum wear can create enough space for pistons to slip out of the cylinder bore utterly. At this point, your drum brakes won’t work at all.

5. Cracked Cylinder Body

Older wheel cylinders can split and crack under pressure, leak brake fluid, and compromise function.

Note: While it seems like a relatively simple component, replacing or fixing a bad wheel cylinder isn’t straightforward because of its location and how it works with the rest of your drum brake system.

Now that you understand how wheel cylinders work, what can go wrong with them, and how to fix them, let’s review some FAQs.

7 Wheel Cylinder FAQs

Here are a few answers to your questions about wheel cylinders:

1. How Many Wheel Cylinders Does a Car Have?

That depends on how many drum brakes your vehicle has and the brake cylinder configuration used.

Generally, a vehicle with drum brakes will have two dual piston wheel cylinders. That’s because cars with a drum brake typically only use it as a rear brake.

2. How Long Does a Wheel Cylinder Last?

You can expect your wheel cylinders to last around 3-5 years or up to approximately 100,000km. This estimate will depend on the make and model of your vehicle and the type of driving done.

Heavy-duty driving (like towing or mountainous terrain) will wear down your wheel cylinder faster.

3. Will My Brakes Still Work if the Wheel Cylinder Fails?

Yes, your brakes will still work, but you’ll experience poor brake response.

Most cars have a dual circuit braking system — meaning if one circuit fails (as in a rear wheel cylinder goes bust in a wheel), there’s still braking capability in the other circuit.

Remember that your brakes won’t be as powerful if the rear wheel cylinder is damaged. The braking distance will be longer, and if you have disc brakes on the front, the rear of your car might jump if you brake hard.

4. If My Wheel Cylinder Leaks, Do I Need to Replace the Brake Shoes Too?

A brake shoe replacement is only necessary if they are too thin or saturated with brake fluid from a leak.

If there’s not too much fluid on the brake shoe, it can still be cleaned up quickly and reliably.

5. Is it More Cost Effective to Replace the Wheel Cylinder with the Brake Shoes?

For the most part, yes.

If you replace the wheel cylinder during a brake shoe job, the new wheel cylinder and labor cost will typically be included in a package price.

The labor time spent replacing the brake shoes and wheel cylinder overlap, so a wheel cylinder replacement is a relatively small additional labor charge.

6. How Much Does a Wheel Cylinder Repair Cost?

Replacing a pair of wheel cylinders on most vehicles costs around $159 to $194. Parts are typically around $64-$75, while labor costs are a little higher, estimated between $95-$119.

7. What Is a Wheel Cylinder Rebuild Kit?

The wheel cylinder can also be rebuilt by mechanics instead of replaced.

It can cost slightly less than a replacement and is sometimes needed for custom or classic cars.

A “wheel cylinder rebuild kit” is just a rebuild kit that has all the parts (pistons, seals, etc.) needed to rebuild the wheel cylinder of your specific vehicle year, make, and model.

However, most repair shop technicians would recommend a replacement rather than a rebuild kit, as many aftermarket wheel cylinders match OE specifications these days, so a rebuild isn’t unnecessary.

Additionally, note that rebuilding requires tons of care and time, specialized mechanical knowledge, and is not always doable if your wheel cylinder is too damaged.

Closing Thoughts

While the brake wheel cylinder rarely causes problems, it can fail with regular wear and tear. To keep your drum brakes healthy, ask your mechanic to take a look whenever you’re getting your brake pads inspected.

And if you’re looking for easily accessible help, just contact AutoNation Mobile Service.

AutoNation Mobile Service is a convenient mobile vehicle repair and maintenance solution with competitive and upfront pricing. Our expert technicians can assist you with brake wheel cylinder issues and brake shoe replacement right from your driveway.

Fill out this online form for an accurate estimate of wheel cylinder replacement and repairs.