Skip the auto shop - Our mechanics make house calls

How Drum Brakes Work

How Drum Brakes Work

Drum brakes are one of two broad categories of brakes on modern vehicles. They are most often seen on the rear of the vehicle while disc brakes operate the front of the vehicle. They are similar to disc brakes in the fact that they are designed to help the vehicle stop quickly and safely. They have several features that make them unique.

The Components of a Drum Braking System

Drum brakes are made up of several components that include the backing plate, the drum itself, the brake shoe, the wheel cylinder as well as several pins and springs.

  • Backing Plate: This is the base for the rest of the components, which is attached to the axle sleeve. The wheel cylinder and brake shoes attach to the surface of the backing plate.

  • Brake Drum: This component is often made of cast iron that is resistant to wear and can conduct heat. It has the job of rotating the wheel and the axle.

  • Wheel Cylinder: One wheel cylinder is needed for each brake. One piston is connected to each end of the cylinder to operate the brake shoes. The cylinder applies pressure to the pistons to push the brake shoes towards the drum for stopping.

  • Brake Shoe: Often made of steel, the shoe consists of two pieces that are welded together with a lining attached either by rivets or adhesive. Three V-shaped notches are located on each side and are often known as nibs. They rest against the support pads that are on the backing plate. The shoes are installed to these pads. One shoe is placed closer to the front of the vehicle and is called the primary shoe. The secondary shoe is just a little further back. Many times, the two shoes are interchangeable.

  • Automatic Adjuster: This component fills the space between the drum and brake shoes as the shoes wear down with use.

In addition to the parts that make up the drum brake, the system also includes a mechanism to operate the emergency brake.

How the Parts Work Together

The driver applies pressure to the brake pedal inside the vehicle, which sends hydraulic pressure from the master cylinder to the pistons. The master cylinder is the main component of the braking system and is different from the wheel cylinder which operates only one brake. The pistons are pushed towards the shoes, which presses them against the drum. This forces the vehicle to stop.

When the driver removes his or her foot from the brake pedal, the springs cause the shoes to go back into place. They do not move very far away unless the components are worn. When this happens, the driver will have to press the brakes down farther to release enough fluid to travel to the pistons.

Using the Emergency Brake

The emergency brake is connected with a cable that pulls on a lever that is attached to the shoes. When the emergency brake is applied, the lever forces the shoes apart. The lever provides direct control rather than going through the wheel cylinder, which allows the vehicle to stop even if the regular brakes have failed.

Wear on the Drum Brake

Because the shoes are doing the most work in this system, they wear down over time and require replacing. If they are left on for too long, the drum may be damaged. In many cases, the drum can be salvaged and sanded down to fit new brake shoes.

Symptoms of issues with Drum Brakes

  • Sponginess in the brake pedals 
  • Noise when pressing the brakes coming from the rear brakes
  • Shuddering in the vehicle when pressing the brakes
  • Excessive rust or corrosion on the brake drum

These symptoms indicate that one or more components of the drum braking system needs to be repaired or replaced by a professional. 

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.


Post a question and get free advice from our certified mechanics.


More related articles

P0121 OBD-II Trouble Code: TPS "A" Circuit Range Performance Problem
P0121 code definition Throttle Pedal Position Sensor/Switch (TPS) A Circuit Range Performance Problem What the P0121 code means P0121 is a generic OBD-II code which indicates that the Engine Control...
P0240 OBD-II Trouble Code: Turbocharger Boost Sensor B Circuit Range/Performance
P0240 code definition Turbocharger Boost Sensor B Circuit Range/Performance What the P0240 code means P0240 is an OBD-II generic code triggered when the Engine Control Module (ECM) detects the intake boost...
How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...

Related questions

Q: How do I turn off the StabiliTrak?

The traction control system (TCS) and StabiliTrak system are crucial parts of your vehicle’s safety. TCS and StabiliTrak limit wheel spin, and keep your vehicle driving securely and safely, especially in adverse weather conditions. However, you can turn off the...

Q: Car making a dragging noise

You may have a brake issue or a wheel bearing issue. Either of them may cause a dragging noise. Attest drive and visual inspection will narrow down what is causing your issue. I would not recommend driving the vehicle. A...

Q: Brakes grab and lock up occasionally - 1990 Chevrolet G30

Make sure the brake pushrod has some freeplay, how ever small. Also check the "check valves" on the hydroboost system to make sure they are releasing residual pressure appropriately.