Curious about how a drum brake works?
Drum brakes form an important part of your car’s rear axle braking system. And while they serve the same purpose as a rear disc brake, they work differently.
Without them, your car wouldn’t be able to stop!
Let’s explore everything you need to know about the drum brake system. We’ll discover what drum brakes are, how they work, and what you should do to keep them in perfect condition.
This Article Contains:
(click on specific links to jump to a particular section of the page)
- What Are Drum Brakes?
- What Are The Main Components Of Drum Brakes?
- How Does A Drum Brake Work?
- The 3 Different Types Of Drum Brakes
- What Should Your Mechanic Check To Keep Your Drum Brakes In Good Condition?
- How To Fix Your Drum Brakes
Let’s get started.
What Are Drum Brakes?
It uses the friction the brake shoe pads generate when they rub against a rotating cylinder-shaped brake drum. This braking force or 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 rear 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 from cast iron or aluminum bolted to the wheel’s hub. They rotate 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. Every drum brake has a pair of brake shoes — a front brake shoe (leading shoe) and a rear brake shoe (secondary shoe.)
These shoes contain friction material inside the brake lining that pushes against the brake drum to stop the vehicle.
Tip: Using brake hardware or brake kits helps reduce noise, vibration, and premature pad wear and tear.
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 retracting spring pulls the brake shoes away from the drum’s friction surface when you let go of the brake pedal.
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 wheel cylinder piston 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 drum’s inner surface, the wheel’s motion 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.
On the other hand, when the driver pulls the brake lever in a parking brake (e-brake) with drum brakes, the cables pull another lever to compress the brake shoes.
As a result, the force from the parking brake lever keeps the vehicle at a standstill.
The 3 Different Types Of Drum Brakes
Here are the three main types of drum braking systems 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, bringing 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 your vehicle’s brake pedal, the fluid in the master cylinder increases the hydraulic force sent to the wheel cylinder. This forces the brake outwards. Then, the wheel cylinder piston (instead of a cam) pushes the brake shoes, and the friction generated by the brake shoe rubbing against the drum decelerates the wheel.
The hydraulic disc brake relies on a similar principle, but the disc brake design is far superior to drum brakes. The disc brake system uses a slim rotor and caliper to stop your vehicle instead of housing the key components within a metal drum.
3. Pneumatic Assisted Drum Brakes
Pneumatic assisted drum brakes or air brake systems are similar to hydraulic brakes but use air instead of fluid in the braking system.
High-pressure compressed air actuates a pneumatic piston and turns the cam, slowing 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 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 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
Compared to a disc brake, the friction material on a drum brake pad wears less easily due to its larger friction contact area.
But their closed nature means more brake dust accumulates, which can affect braking power if not removed. That’s why you must get a mechanic to regularly inspect and clean the whole brake assembly 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 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 rear drum brake system can get compromised every time there’s a brake fluid leak in the:
- Master cylinder
- Brake fluid reservoir
- Wheel cylinder
- Brake line, or
- Brake hose
Additionally, if any moisture collects in the fluid or 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.
Also known as rubber rings, seals serve two functions:
- They stop the hydraulic brake fluid from leaking out of the caliper (AKA backing plate)
- They guard the fluid against moisture and contaminants
If your seals get damaged, you might face a brake fluid leak or have contaminated fluid — both of which can make the brake fade.
They are subject to constant pressure and flex, allowing the wheel cylinder and backing plate to move up and down with the vehicle’s frame.
However, over time, brake hoses can become worn out.
They can develop cracks, tears, or even loose hanging threads, weakening the hose’s 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 it to a garage.
Brakes are highly crucial to your vehicle’s safety, and you can’t afford to compromise on the quality of your replacements. You’ll want to make sure they clean the whole brake assembly, including the rotors, brake shoe lining, and friction material, with the correct brake cleaner.
And fortunately, you can easily find a mechanic that can do this for you:
AutoNation Mobile Service is the most convenient mobile car repair and maintenance solution.
Here’s why you should turn to AutoNation Mobile Service for your repairs:
- You can get your brakes fixed in your driveway without having to take your car to a repair shop
- Expert, certified mechanics will service your car
- We use only high-quality equipment and replacement parts
- You can book an appointment online in just a few clicks and benefit from upfront and competitive pricing
- All repairs come with a 12-month, 12,000-mile warranty
Fill out this online form for a free quote on how much your repair could cost.
The drum brake system is vital 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 AutoNation Mobile Service, you can get qualified technicians to manage your rear drum brake repair— right in your driveway.