how do rear drum brakes work

How Do Rear Drum Brakes Work?

Rear drum brakes are a vital component of many vehicles, especially those that prioritize cost-effectiveness and reliability. Understanding how these brakes function can provide insights into their design and maintenance.

At first glance, the drum brake system differs significantly from its disc brake counterpart. A rear drum brake consists of a round drum that is mounted on the wheel hub. When you apply the brakes, the brake shoes, which are curved pieces of metal lined with friction material, press outward against the inside of the drum, creating friction that slows down or stops the vehicle.

Components of Rear Drum Brakes

To understand how rear drum brakes work, it is essential to familiarize yourself with their main components

1. Brake Drum This is the cylindrical component that rotates with the wheel. Its inner surface is lined with friction material that interacts with the brake shoes.

2. Brake Shoes These are curved components with a friction lining that press against the inner surface of the drum when the brake is applied.

3. Wheel Cylinder This hydraulic component is activated when the driver presses the brake pedal. As brake fluid is forced into the cylinder, it moves the brake shoes outwards against the drum.

4. Adjustment Mechanism Drum brakes often feature an automatic adjustment mechanism to maintain the correct distance between the shoes and the drum as the shoes wear down.

5. Return Springs These springs pull the brake shoes back to their resting position when the brake is released, ensuring they do not drag against the drum.

The operation of rear drum brakes can be broken down into several steps

1. Brake Actuation When the driver engages the brake pedal, brake fluid is sent from the master cylinder into the wheel cylinder, which activates the rear brake system.

2. Expansion of Brake Shoes The hydraulic pressure in the wheel cylinder forces the brake shoes outward against the inside of the brake drum. The friction between the shoes and the drum creates the necessary force to slow the vehicle.

3. Friction Generation As the brake shoes push against the drum, the friction generated slows the drum's rotation, which in turn slows down the wheel connected to it.

4. Heat Dissipation The friction created during braking generates heat, which is dissipated through the drum. Because drum brakes can trap heat more effectively than disc brakes, they can experience brake fade—reduction in braking effectiveness—if overheated.

5. Releasing the Brakes Once the driver releases the brake pedal, the hydraulic pressure is removed, and the return springs pull the brake shoes back to their original position, allowing the wheel to rotate freely again.

Advantages and Disadvantages

Rear drum brakes have several advantages. They are generally less expensive to manufacture than disc brakes, and they provide adequate stopping power for many vehicles. Additionally, they are often more effective in holding the vehicle stationary, making them common in parking brake designs.

However, there are also drawbacks. Drum brakes tend to dissipate heat less efficiently and can suffer from brake fade under heavy use. They also tend to require more maintenance to ensure the adjustment mechanism remains functional and to replace worn friction material.

Conclusion

Understanding how rear drum brakes work is crucial for both vehicle owners and aspiring automotive technicians. While they may not be as commonly found in modern performance vehicles, they remain a reliable and economical choice for everyday driving. Regular maintenance and inspection can help ensure that drum brakes function properly and safely, contributing to the overall reliability of the vehicle.