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Drum brakes are a type of braking system that uses the friction that the brake shoe pads generate when they rub against a rotating cylinder-shaped brake drum. This braking force or friction converts kinetic energy into thermal energy and decelerates the vehicle.
The brake drum, wheel cylinder (brake center), pistons inside the wheel cylinder, shoes, pads, and return springs make up the drum brake system. They are a complex part of a braking system and require more maintenance than disc brakes.
Brake Shoes
A brake drum is the center component of a brake system, found on many vehicles. It contains a pair of long, curved brake shoes that are pushed outward against the inside of the drum to generate friction, which slows and stops the vehicle.
Brake drums are made of cast iron, aluminum or sometimes a combination of these materials. Their inner surface is coated with a high-drag material like graphite, powdered metals or crushed up cashew nut shells.
When the pedal is pressed, hydraulic pressure from the wheel cylinder pushes the brake shoes outward against the drum’s inner surface. The friction between the linings and drum generates a lot of heat.
This heat is dissipated by the brake drum, and it prevents the linings from overheating and fading. However, it also means that the braking process takes longer and requires more effort. This can cause a decrease in driver confidence and can be a safety hazard for drivers.
Wheel Cylinders
Wheel cylinders are a vital part of the hydraulic brake system. They're located at the upper level of each wheel, and their job is to push brake shoes into contact with a rotating drum.
This generates friction, which slows down or stops the vehicle. As soon as you press the brake pedal, a master cylinder transfers the force to a pair of pistons inside each wheel cylinder.
The coerced brake fluid then shoves each of these pistons outside of the cylinder, forcing each of these pistons to press against the brake drum, stopping the wheel.
Wheel cylinders typically incorporate two pistons, but some drum brake configurations use one single-piston cylinder at the top of the drum and another at the bottom connected to a brake shoe. Regardless of which type is used, older wheel cylinders can split or crack under pressure, and this can severely limit their ability to apply the brakes. Moisture can also build up inside wheel cylinders, which can lead to leaks and corrosion.
Return Springs
Drum brakes use hydraulic pressure to generate friction, which slows or stops a vehicle. They are used in passenger cars and light trucks as well as some large trucks, especially those with rear-wheel drive.
The drum brake system is made up of a wheel cylinder, brake shoes and springs. The pressurized hydraulic brake fluid opens the pistons on the right and left of the wheel cylinder on both sides and pushes against the shoes to apply brakes.
Brake shoes are half-moon shaped metal pieces with linings on the outside and a high friction coefficient on the inside. The piston on the cylinder pushes the brake shoes to apply brakes and the return spring pulls the shoes back.
The brake shoes in a drum brake assembly are held in place by small coil springs secured by pins that extend through the backing plate and lock into a cover piece. If these are badly corroded, the springs may break or fall apart causing the shoes to slip out of place and possibly cause damage to the drum or the braking system.
Brake Pads
Brake pads are designed to grab hold of brake rotors, creating friction that slows or stops the vehicle. Once the brake pedal is pressed, a master cylinder sends brake fluid to the calipers where one or more pistons squeeze brake pads against a disc rotor to produce the clamping force required to stop the vehicle.
There are various types of brake pads, ranging from non-metallic to fully metallic compounds. The best pad for your particular braking needs depends on the type of vehicle and the kind of driving you do. Some pads are more aggressive and durable than others, requiring more brake pedal pressure to generate the same level of braking torque.
