Drum brakes are usually used as rear brakes in automobiles. Let’s go through the parts involved in the system and see how it works in detail.
Brake Drum — Acts as the braking surface on the wheel side.
Wheel Hub — The part to which the drum and the wheel are attached to
Let’s have a closer look with the wheel hub off.
Backplate — This holds all the brake components together.
Brake Shoes — These will be pushed against the inner surface of the drum The friction between the lining and the drum is what makes the wheels slow down.
Hold Down Spring — Holds the brake shoes towards the backplate
Retaining Springs — Returns the brake shoes to their resting position
Wheel Cylinder — The hydraulic part which pushes the brake shoes.
Modern drum brake systems are self-adjusting. This means when the lining wears out, the system adjusts the brake shoes towards the drum For that, the system uses a Brake Adjuster, Adjuster Lever, Adjuster Spring.
The wheel cylinder receives the force that we applied on the brake pedal At the back of the wheel cylinder. There is an inlet port to receive the fluid and a bleeder valve to remove air from the system.
Let’s have a look at the exploded parts view
- Cylinder Body
- Dust Boots
- Pistons
- Piston Cups
- Piston Cup Expanders
- Return Spring
When force is applied on the brake, the hydraulic fluid pushes the wheel cylinder pistons which pushes the brake shoes. This action creates friction between the brake liner and the inner surface of the drum and brings the automobile to rest.
The adjuster makes sure that the brake liners remain close to the drum as the liners wear down. As you can see, it uses a screw mechanism to increase its length between the shoes Each time the car breaks while in reverse, the cog is pulled down by the pin to push the shoes against the drum. And that’s how a drum brake system works.
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