11 Brake System Parts (and Their Functions)
A vehicle’s braking system allows the driver to brake and stop smoothly and reliably. Car brakes work by converting the kinetic energy of motion into thermal energy (heat).
Every time you press the brake pedal, the speed of the wheels rotating under the vehicle decreases in proportion to the pressure you apply to the pedal. Vehicles are equipped with disc brakes or drum brakes to provide the necessary friction.
Modern automotive braking systems are called servo brake systems. These systems use a brake booster that amplifies the force applied to the brake pedal, making braking much easier for the driver. With power braking, a slight pressure on the brake pedal slows the vehicle.
In a classic mechanical braking system, there was a cable that connected the brake pedal to the brake shoe assembly. When the driver pressed the brake pedal, it pulled the cable, slowing down the rotating brake drum. It was used in automobiles in the early 20th century and is still used today on bicycles.
Components of an Automobile Brake System
Below is a list of the major parts of an automobile brake system. It includes both disc brake system components and drum brake system components. Most modern vehicles have disc brakes on all four corners, but some small cars still have drum brakes in the rear.
1) Brake Master Cylinder
The master cylinder pushes hydraulic fluid from the brake fluid reservoir into the brake lines. Most master cylinders are split into two or more separate cylinders for safety reasons. Typically, each cylinder controls braking force for one front wheel and the opposite rear wheel. This way, if one cylinder fails, the other can still slow the car and the driver can maintain a reasonable level of control over the vehicle.
Some vehicles use one cylinder per axle (split front/rear). Others use multiple cylinders per wheel for maximum redundancy in the event of a failure. The master cylinder works by adjusting the hydraulic pressure applied to the hydraulic fluid. More pressure means a faster vehicle speed.
2) Brake Disc (Disc Brake)
Each wheel on a vehicle has a brake disc that rotates while the vehicle is moving. The brake pads and caliper come into contact with the disc, creating the friction needed to slow it down. This action slows down the wheel and the entire vehicle. Brake discs are usually made of cast iron. Cast iron is very heavy, but it also absorbs a significant amount of heat. To help dissipate the heat, many brake discs are equipped with vents.
These ventilated brake discs have openings or slats between the two discs. These vents direct airflow into the brake disc, effectively cooling it as it spins. Rear brakes usually use solid rotors because they have less work to do when stopping a vehicle.
3) Brake Drum (Drum Brakes)
If you have a drum brake system, the brake drum takes the place of the brake rotor. So how does it work?
When the wheels of your car rotate, the brake drum components rotate with them. When you apply the brakes, the brake shoes press against the inside of the drum, creating friction that stops the car. It’s a simple but effective system that has been around for decades.
And for those who prefer the simplicity of this type of braking system, brake drums remain a reliable and effective alternative to more modern brake rotors.
4) Brake Pads (Disc Brakes)
In a disc brake system, friction is created when the brake pads and their calipers rub against the rotating brake disc. Brake pads are made from different materials, which affects their lifespan and optimal heat range. Brake pads used outside of the correct temperature range can increase stopping distances.
5) Brake Caliper (Disc Brake)
The brake caliper creates the clamping force that presses the brake pads against the brake disc. This is achieved by hydraulic pressure.
Hydraulic pressure from the master cylinder forces brake fluid through the brake lines and into one or more pistons in the brake caliper. When you apply the brakes, these pistons press with great force against the brake pads.
6) Brake Shoes (Drum Brakes)
If you have a drum brake system, this is an alternative to brake pads. Unlike brake pads, which are flat and attached to the brake caliper, brake shoes are curved and fit into the brake drum. As the drum rotates, the brake shoes press against the drum, creating the friction needed to stop your car.
7) Brake Booster
The brake booster (also called a vacuum servo) is part of a power brake system that uses engine vacuum or a vacuum pump to boost the pressure of your foot on the brake pedal.
This means you don’t have to apply as much force to the pedal to slow your vehicle. It’s like an aid to make braking easier and more efficient. Brake boosters are very important for modern cars, making it easier for drivers to brake smoothly and quickly in any situation.
8) Brake Pedal
The brake pedal is one of the most important components of your car’s braking system. Located next to the gas pedal, it’s the pedal you step on to slow down or stop your vehicle. But did you know that the brake pedal is connected to the entire braking system on the inside?
When you press down on the brake pedal, it activates the master cylinder, which in turn sends hydraulic fluid to the brake calipers or wheel cylinders. This creates friction between the brake pads and rotors, or brake shoes and drums, which slows down your vehicle.
9) Wheel Speed Sensors (ABS)
Vehicle equipped with an anti-lock braking system (ABS) have wheel speed sensors which detect how fast each wheel is spinning. If your wheels lock up because you slam on the brakes, one or more wheels will be spinning at different speeds.
10) ABS Module
An ABS module is a computer for the braking system. This computer modulates the brakes when one or more tires are at the limit of traction on vehicles equipped with anti-lock brakes.
The ABS module uses input from the wheel speed sensors and possibly other sensors, depending on the manufacturer’s programming. When a tire starts to lock up, the ABS module will release brake pressure to that specific wheel, allowing the tire to regain traction.
Remember that a rolling tire has more grip than a sliding tire. The ABS system gives a driver the ability to stop as fast as possible, even when they stand on the brakes as hard as they can.
11) Brake Lines
Brake lines transfer brake fluid between the master cylinder and wheels. This is the hydraulic fluid that allows braking to be so easy. Unlike air, hydraulic fluid is not compressible.
A brake fluid leak is potentially dangerous as it may introduce air in the system. When there is no brake fluid, the brakes will not work effectively.
