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Everything You Need To Know About Drum Brakes (2021)

March 24, 2021

Curious about how drum brakes work?

Drum brakes are usually used in a car’s rear axle and form an important part of your braking system. While they work a little differently than a rear disc brake – they serve the same purpose.

Without them, your car wouldn’t be able to stop!

In this article, we’ll discuss everything you need to know about drum brakes. We’ll cover what they are, how they work, and also what you should do to keep your drum brakes in perfect condition.

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Let’s get started.

What Are Drum Brakes?

A drum brake is a type of brake used in many vehicles – especially in rear brakes.

It uses the friction generated by brake shoe pads when they rub against a rotating cylinder-shaped brake drum. This friction converts kinetic energy into thermal energy and decelerates the vehicle.

It’s important to note that the whole drum brake assembly is usually fitted to the back plate of the wheel and does not rotate with the backing plate.

What Are The Main Components Of Drum Brakes?

Let’s look at the different drum brake components:

1. Brake Drum

Brake drums are large metal discs made of cast iron or aluminum that are bolted to the hub of the wheel. They rotate along with the hub and form a frictional pair with drum brake shoes to slow your car down.

2. Brake Shoe

The brake shoe or brake pad is a curved piece of metal fitted on the rear wheel. These pads contain friction material inside the brake lining that pushes against the brake drum to stop the vehicle.

3. Wheel Cylinder

The wheel cylinder of your brake system contains a piston that moves outwards when the brakes are applied. The force of the piston pushes the brake shoe outwards and decelerates your vehicle. 

4. Return or Retracting Spring

A return or a retracting spring pulls the brake shoes away from the drum’s friction surface when you let go of the brake pedal.

5. Self Adjuster

The self adjuster maintains the minimum gap between the brake shoe and drum to avoid contact with each other.

How Does A Drum Brake Work?

When you step on the brake pedal, your master cylinder compresses its fluid, and the piston of the wheel cylinder expands outward. The outward motion of the piston forces the brake shoe to press against the brake drum.

Just as the brake shoe lining touches the inner surface of the drum, the motion of the wheel reduces, and the vehicle stops.

When you take your foot off the brake pedal, the retracting springs draw the brake shoe inward — removing the contact between the drum brake lining and the shoe. 

The 3 Different Types Of Drum Brakes

Here are the three main types of drum brakes that are used today:

1. Mechanical Drum Brakes

These are primarily used in two-wheelers.

In mechanical brakes, when you press the brake pedal, the brake cam turns, pushing the brake shoe outwards and rubbing it against the drum.

The friction between the brake linings and the drum slows down the rotation of the wheel — stopping the vehicle. 

When you release the brake pedal, the brake spring retracts and brings the brake shoe back to its original position. 

2. Hydraulic Drum Brakes

These drum brakes operate through the hydraulic pressure in your brake system.

When you press down on the brake pedal of your vehicle, the oil in the master cylinder increases the hydraulic force sent to the wheel cylinders. This forces the brake outwards. 

Then, the wheel cylinder’s piston (instead of a cam) pushes the brake shoes, and the friction generated by the brake shoe rubbing against the drum decelerates the wheel.

3. Pneumatic Assisted Drum Brakes

Also referred to as air brake systems, these are similar to hydraulic brakes, but they use air, instead of fluid, in the braking system.

High-pressure compressed air actuates a pneumatic piston and turns the cam, which slows down your wheel. 

These brakes are mostly found in heavy commercial vehicles such as heavy-duty trucks, buses, railroad locomotives, etc., because of their stopping power. 

Tip: Did you know that there are different types of brake pads too? Check out this guide on ceramic vs. semi-metallic brake pads.

What Should Your Mechanic Check To Keep Your Drum Brakes In Good Condition?

Brake drums on your car are typically built to last for about 200,000 miles. 

However, in some cases, your drum brakes may wear out sooner than that.

But don’t worry.

Here are some things that your mechanic might have to check to ensure that your drum brake remains functional:

1. Friction Material

The friction material on the brake shoe can get worn out over time and compromise your drum brake’s effectiveness.

That’s why it’s important that you get a mechanic to inspect them regularly and not wait till your worn brake shoe starts rubbing against the metal drum.

2. Brake Fluid

Also known as hydraulic fluid, brake fluid is the conduit for most of the processes in your vehicle’s braking system. Without it, your brakes wouldn’t be able to generate the hydraulic pressure and braking force needed to stop your car.

Often, the hydraulic pressure in your drum brake system can get compromised every time there’s a brake fluid leak in the:

Additionally, if any moisture collects in the fluid or if any contaminants seep in, it can get contaminated — affecting the ability of rear drum brakes to perform effectively. 

That’s why it’s always a good idea to have your brake fluid checked (or changed) at least once a year. 

3. Seals

Also known as a rubber ring, seals serve two functions:

If your seals get damaged, you might face a brake fluid leak or have contaminated fluid — both of which can make the brake fade.  

4. Hoses

The brake hose carries the brake fluid from the brake line to the brake caliper in the wheel. 

They are subject to constant pressure and flex, allowing the wheel cylinders and calipers to move up and down in relation to the vehicle’s frame. 

However, over time, brake hoses can become worn out. 

They can develop cracks, tears, or even loose hanging threads, all of which weaken the hose and its ability to hold pressure. This, in turn, makes it more susceptible to developing leaks. 

5. Dust Boots    

Your brake components are constantly exposed to road debris and brake dust. 

Dust boots prevent dirt and other contaminants from entering the caliper piston.

If the boots are damaged and can’t do their job, your brake piston gets stuck. This results in worn rear drum brakes – which can’t function effectively.

How To Fix Your Drum Brakes

If you’re facing any drum brake issues, it’s always safer to take your car to a repair shop or call a mobile mechanic to come over if you don’t have the time to take your vehicle to a garage.

Why? 

Brakes are highly crucial to your vehicle’s safety, and you can’t afford to compromise on the quality of your replacements.

However, when you’re hiring a mechanic, ensure that they:

Fortunately, you can easily find a mechanic that fits all these criteria:

RepairSmith is the most convenient mobile car repair and maintenance solution.

Here’s why you should turn to RepairSmith for your repairs:

Simply fill out this online form for a free quote on how much your repair could cost.

Wrapping Up

Drum brakes play a vital role in keeping you and your car safe.
So keep an eye out for any problems in the parts we mentioned earlier, as they could signal major issues with your brakes.

Luckily, with RepairSmith, you can get qualified technicians to manage your rear drum brake repair— right in your driveway.