Drum brake system

The working principle of a drum brake system involves converting hydraulic pressure from the brake pedal into mechanical force to stop or slow down the wheel. 

1. Pressing the Brake Pedal

• When the driver presses the brake pedal, it activates the master cylinder.

• The master cylinder pushes brake fluid through the brake lines towards the wheel cylinders in each drum brake.

2. Hydraulic Pressure in the Wheel Cylinder

• The brake fluid creates hydraulic pressure in the wheel cylinder, located inside the drum brake assembly on each wheel.

• The wheel cylinder contains two pistons positioned at either end.

3. Expanding Brake Shoes

• Hydraulic pressure pushes the pistons outward, causing the brake shoes to move away from each other.

• The brake shoes are lined with friction material and are mounted with a slight arc, allowing them to contact the drum surface evenly.

4. Contact with the Brake Drum

• The outward movement of the brake shoes forces them to press against the inner surface of the drum, which rotates along with the wheel.

• Friction is generated between the brake shoes and the rotating drum. This friction slows down the rotation of the drum and, consequently, the wheel attached to it.

5. Self-Energizing Effect

• In a drum brake, the frictional force between the shoes and the drum often creates a self-energizing effect.

• As the drum rotates, it pushes the leading edge of one shoe harder against the drum, amplifying the braking force with minimal pedal effort.

6. Deceleration and Stopping

• The friction force generated between the shoes and the drum converts the vehicle's kinetic energy into heat, slowing down the wheel.

• The braking process continues until the wheel slows down to the desired speed or stops completely.

7. Releasing the Brakes

• When the driver releases the brake pedal, the hydraulic pressure in the wheel cylinder drops.

• Return springs attached to the brake shoes pull them back to their original positions away from the drum.

• This releases the friction between the brake shoes and drum, allowing the wheel to rotate freely again.

8. Heat Dissipation

• During braking, a large amount of heat is generated due to friction.

• Unlike disc brakes, drum brakes are enclosed, which limits airflow and makes them less effective at dissipating heat.

• This can lead to brake fade in situations where continuous braking is required, as the drum brake’s friction surfaces can overheat and lose effectiveness.