Applied at the brake pedal, the driver's braking effort is multiplied by the brake booster and then applied to the master cylinder. The brake master cylinder transmits the braking effort—via the brake fluid—to the brake calipers (on disc brakes) or to the rear wheel cylinders (on non-disc brakes). Consistent with the driver's pedal effort, first the calipers press the brake pads against the brake rotors. Then, the brake wheel cylinders apply the brake shoes against the brake drums, thereby braking the car.
Most new vehicles have anti-lock brakes (ABS) for faster, safer braking. The parking, emergency brake can be used as a mechanical or electronic backup in case the hydraulic system fails.
Braking System Components
Brake fluid transmits the force from the brake pedal to each wheel. Brake fluid degrades over time and needs to be replaced as a part of regular car maintenance. Check your owner’s manual for the recommended service intervals.
The brake master cylinder is linked to the brake booster to the brake pedal. It regulates the brake fluid pressure exerted onto the brake discs or drums. When the brake pedal is pressed, the brake master cylinder creates hydraulic pressure in the brake lines and brake hoses. This pressure pushes pistons in the brake caliper that force the brake pads against the rotors. On drum brakes, the wheel cylinders force the brake shoes against the drums. The harder you press on the brake pedal, the greater the pressure created by the master cylinder, and the faster the vehicle stops.
It requires a significant amount of force to stop a car. It would be difficult for a typical driver to produce this force without a brake booster. Located between the brake pedal and the brake master cylinder, the brake booster is powered by the vacuum created by either the engine, or an electric pump, or hydraulic fluid.
Nearly all modern cars are equipped with disc brakes at the front wheels. Disc brakes include 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 vehicle.
Drum brakes are more likely found on older vehicles, although some modern cars still use them in the rear. Drum brakes include 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 vehicle.
If you’ve ever felt and heard the electronic pulsation of your brakes under heavy braking, you’ve experienced anti-lock brakes (A.B.S.). First introduced in the 1970s, they're now standard on almost all vehicles, and for good reason. Skidding wheels have less traction and won't turn as well as non-skidding wheels. In slippery conditions or under heavy braking, A.B.S. help keep your wheels from skidding, so you can stop faster while still being able to steer. An ABS control module continually measures the speed of each wheel. With the help of a wheel speed sensor, the module is able to tell when a wheel is starting to skid. If it senses that the wheel is locking up, the module temporarily releases and applies brake pressure with as many as fifteen pulsations per second to slow both the wheels and car as quickly and safely as possible.
The parking/emergency brake can be used as a non-hydraulic brake system backup. It can be either cable or electronically operated. By pressing the parking brake pedal or pulling the parking brake lever, a cable is pulled to activate the rear brakes. The cable may operate the existing brakes, or it may have its own assembly inside the hub of the rear brake rotors.
Brake system repairs
Most people don't think about our car's brakes until we need them for a panic stop, hear a screeching or grinding noise, or when a warning light comes on. Brakes are worn down every time you drive your car. It's important to keep them maintained and serviced, before you hear that screeching. The sooner the better and cheaper.
All vehicles incorporate some type of brake warning system to inform the driver of a problem. A warning light is the most common. It typically alerts a driver of:
- Low brake fluid
- Brake system hydraulic pressure failure
- An applied parking brake
- An anti-lock brake malfunction
- Worn Brake pads
- An inoperative brake light bulb
Some brake systems have metal clips that rub on the brake rotors when brake pads are worn out. This causes a high-pitched, fingernails-on-a-chalkboard screech when the brake pedal is pressed. Some newer vehicles alert the driver in a more civilized and agreeable manner with warning lights or computerized messages. No matter which your car has, it's critical to address the issue promptly.
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