The master cylinder is linked to the brake booster and, in turn, to the brake pedal. It regulates the fluid pressure exerted onto the brake discs or drums. When the brake pedal is pressed, the master cylinder creates hydraulic pressure in the brake lines. This pressure pushes pistons in the caliper that force the brake pads against the rotors. On drum brakes, the wheel cylinder forces the brake shoes against the drums. The harder the brake pedal is pressed, the greater the pressure created by the master cylinder, and the faster the car stops.

It takes a significant amount of force to stop a vehicle. It would be very difficult for a typical driver to produce this force without a brake booster. Located between the brake pedal and the master cylinder, the booster is powered by the vacuum created by either the engine or an electric pump. Nearly all modern vehicles are equipped with disc brakes on their front wheels. Disc brakes consist of a brake rotor (disc), a brake caliper, and two brake pads per wheel. Friction is generated when the calipers force the pads against the rotors, thus slowing the rotation of the wheel and the car.

Drum brakes are more common on older vehicles, although some modern vehicles still use them in the rear. Drum brakes consist of a wheel cylinder, brake shoe, and a round brake drum that rotates with the wheel. When the brake pedal is pressed, the wheel cylinder pushes the brake shoes outward against the drum. The resulting friction slows the rotation of the wheels and the car.

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