11 Parts of a Brake System (and Their Functions)

The brake system in your vehicle allows the driver to slow down or stop in a consistent and reliable manner. The brakes on your car work by converting the kinetic energy of movement into thermal energy (heat).

Each time you step on the brake pedal, the speed of the spinning wheels underneath your vehicle is reduced proportionately to how much pressure you apply to the pedal. A vehicle will have either a disc braking system or drum braking system to create the necessary friction for this to take place.

Modern car brake systems are referred to as power brake systems. These systems use a brake booster that amplifies the force you apply to the brake pedal. This makes braking so much easier for drivers. Power braking allows you to apply just a little bit of pressure to the brake pedal in order for the vehicle to slow down.

In the classic mechanical brake system, there was a cable which connected the brake pedal and brake shoe assembly together. When the driver stepped on the brake pedal, it pulled on the cable and allowed the brake drum spinning to slow down. This was used on cars in the early 20th century, and is still used on bikes today.

Car Brake System Components

Below is a list of the main components of a car brake system. We have included both the components of the disc and drum brake systems. Most modern vehicles have disc brakes on all four corners, but some economy cars still use drum brakes in the rear.

1) Master Cylinder

bad brake master cylinder

The brake master cylinder pushes hydraulic fluid down into the brake lines from the brake fluid reservoir.

Most master cylinders are actually split into two or more individual cylinders for safety reasons. Typically each cylinder manages the braking ability of one front wheel and the opposite rear wheel. That way, if one cylinder fails, the other cylinder can still slow down the car and allow the driver to maintain a reasonable amount of control.

Some vehicles will use one cylinder per axle (front/rear split). Others use multiple cylinders per wheel for maximum redundancy in case of a failure. 

The master cylinder works by managing the amount of hydraulic pressure that is placed on the hydraulic fluids. More pressure will slow down the vehicle more quickly.

2) Brake Rotor (Disc Brakes)

disc brake rotor

Each wheel has a brake rotor which spins while the vehicle is moving. The brake pad and caliper rub against the rotor and create the necessary friction to slow down the disc. This, in turn, slows down the wheel and vehicle.

Brake rotors are typically made out of cast iron. Cast iron is very heavy but can absorb a lot of heat. To aid in heat dissipation, many rotors are vented. Vented rotors have vents or vanes between the two discs. These vents direct airflow into the rotor, cooling the rotor as it spins. Rear brakes tend to be solid rotors, since rear brakes typically do less of the work to stop a vehicle.

3) Brake Drum (Drum Brakes)

drum brake assembly

The brake drum is the alternative to a brake rotor when you have a drum brake system. As the drum component spins, the brake shoe goes inside and pushes against it when you step on the brake pedal.

4) Brake Pad (Disc Brakes)

brake pad

In a disc brake system, the brake pad and its caliper create friction as they rub against the spinning brake disc.

Brake pads are made out of different materials, that affect their longevity and optimum heat range. Operating a brake pad outside its optimum heat range will likely increase your stopping distance.

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5) Brake Caliper (Disc Brakes)

brake caliper

Brake calipers provide the clamping force that pushes the brake pad into the brake rotor. This is achieved by using hydraulic pressure.

The hydraulic pressure from the master cylinder pushes brake fluid down the brake lines and into one or more pistons housed in the brake caliper. When you step on the brake, these pistons push on the brake pads with a great force. 

6) Brake Shoe (Drum Brakes)

brake shoe

This is the alternative to the brake pad when you have a drum brake system. The brake shoe is what rubs against the interior of the brake drum when you step on the brake.

7) Brake Booster

brake booster

The brake booster (also called a vacuum servo) is part of the power braking system. A brake booster uses engine vacuum or a vacuum pump to amplify the foot pressure that you place on the brake pedal. This makes it easier to slow down the vehicle.

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8) Brake Pedal

brake pedal

The brake pedal should be obvious. This is the pedal next to the gas pedal that you step on to slow down the vehicle. It is connected to the entire braking system on the inside.

9) Wheel Speed Sensors (ABS)

wheel speed ABS sensor

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.

This speed difference is used by the ABS module to determine how to apply individual brakes to bring your car to a safe, controlled stop. 

10) ABS Module

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 fluid leak symptoms

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. That means when you push on the brake pedal, that force is directly transferred to the piston in the brake caliper, or shoe in the brake drum. 

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.

5 thoughts on “11 Parts of a Brake System (and Their Functions)”

  1. I am driving a 25 str coaster bus, the steering shakes when I step on the brakes. Can the stabiliser bushings be the cause or is it the faulty brake system.

    Reply
    • Hard to say without someone seeing it in person. Could be a stuck caliper, bad brake hose, bad master cylinder, bad proportioning valve, or something else entirely. I’d have it looked at by a professional.

      Reply

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