What Is a Drum Brake System, How Does It Work

A drum brake is a braking system used in cars and motorcycles. In this system, when you press the brake pedal, braking is performed by a drum-shaped part located between the brake calipers. This part moves toward the brake shoes, bringing the brake linings into contact with the vehicle’s tire to apply braking. Drum brakes are an older technology than disc brakes, but they are still used in many vehicles. In particular, they are still used on motorcycles, older-model vehicles, and vehicles with cost constraints.

Structure of Hydraulic Drum Brakes

The brake drums rotate together with the wheels, and inside each drum are brake shoes fitted with brake linings. When the pistons press against the drums, they generate braking force from the inside, which slows the wheel’s motion. Friction converts kinetic energy into thermal energy. It’s also important for a drum brake to have adequate ventilation for heat dissipation.

How Does a Drum Brake Work

1- When the driver presses the brake pedal, the piston of the master cylinder moves like a medical syringe, driven through the pushrod. The brake fluid in the master cylinder is then compressed, converting mechanical energy into hydraulic energy.

2- This high-pressure brake fluid is transferred from the master cylinder to the wheel cylinder through the brake lines.

3- When the high-pressure brake fluid enters the wheel cylinder, it moves the cylinder piston, which expands the fixed shoes.

4- Friction then occurs between the brake shoe and the drum lining, converting the vehicle’s kinetic energy into heat energy. The vehicle’s speed then decreases and it stops.

5- When the force is removed from the brake pedal, the return springs pull the brake shoe back inward, and there is no more contact between the friction lining and the drum. The brake is then back in its original position.

An animation showing the structure and operation of a drum brake system in detail. (Above) In this animation you can also see the placement of the parking brake (shown in red).

Self-Energizing Effect

Drum brakes can create a self-energizing effect as the linings drag against the drum.

Parking Brake Integration

Drum brake systems can be easily integrated with a mechanical parking brake mechanism.

Low Cost

Drum brakes are still commonly used on rear axles because their manufacturing cost is lower than disc brakes.

Advantages of the Drum Brake System

The drum brake system has many advantages:

Cost: The drum brake system is cheaper than the disc brake system, making it a less expensive option.
Durability: The drum brake system is more durable than the disc brake system and requires less maintenance.
Simplicity: The drum brake system has a simpler design than the disc brake system and therefore contains fewer parts. This makes it easier to repair in case of a fault.
Reduced air gaps: The drum brake system has less air gap than the disc brake system. This means less energy is needed and it provides a faster response during braking.
Suitability: The drum brake system is a more suitable option than the disc brake system, especially for older-model cars and motorcycles.

Another animation showing the structure and operation of the drum brake system in detail. (above) In this video you can also see the internal structure and operation of the hydraulic wheel cylinder.

Disadvantages of the Drum Brake System

The drum brake system has a few disadvantages compared to the disc brake system. The system can be less safe during braking, because the inner surface of the linings can wear down easily during braking, which can make it less safe.

It has lower braking force compared to disc brakes.
The brakes weaken when applied for a long period.
If the brake gets wet, it takes a long time for the water to drain from the drum, so it won’t work properly.