A TYPICAL AUTOMOTIVE BRAKING SYSTEM
The braking system is designed to help the operator control the deceleration of the vehicle. While the suspension and steering systems control the ride and directional movements, the braking system is designed to slow or stop the vehicle.
PURPOSE OF THE BRAKING SYSTEM
The braking system is crucial to the safe operation of the vehicle. This section identifies brake components and the principles that assist in slowing a vehicle. Purpose of the Braking System The braking system is designed to decrease the speed of the vehicle. In order to slow the vehicle there needs to be friction between parts. Unlike the lubrication system, where minimizing friction is the goal, the braking system is designed to use friction for control. The amount of friction created needs to be controlled by the operator of the vehicle. This is done by the force the operator exerts on the brake pedal. Force is defined as the pushing or pulling action of one object upon another. In this example, the operator’s foot is one object, while the brake pedal is the other object. The brake pedal is mechanically connected to a hydraulic unit called a master cylinder. The master cylinder is where brake fluid is stored. As force is exerted on the brake pedal, fluid is sent to all of the wheels through brake lines. Once at the wheels, the fluid pressure is converted back to mechanical pressure. This pressure causes the brake pads or shoes (discussed later) to move to create the needed friction against a rotating disc or drum at the wheels to slow the vehicle. Friction increases as the operator pushes harder on the brake pedal.
Types of Brakes
The two types of brakes commonly used on the automobile are: • Disc Brakes • Drum Brakes Disc Brake Drum Brake Some vehicles only have disc brakes, but many vehicles have a combination of the two systems. On vehicles with both systems, disc brakes are usually front brakes while drum brakes are usually rear brakes. Disc and drum brake systems use a brake pedal, master cylinder, and brake lines. The major difference between the disc and drum brake systems is the hardware at the wheels. Both disc and drum brake systems use a frictional type material that slowly wears as the brakes are applied. More recently, manufacturers have been installing disc brakes on all four wheels as standard equipment.
Tech Tip
Warped Brakes If a pulsation is noticed when the brakes are applied, the rotors may be warped. Brake rotors can become warped if lug nuts are not tightened to the correct torque. The rotors can also become warped if cold water comes in contact with them immediately after the brakes have been used excessively.
Disc Brakes The disc brake system consists of a disc, also called a rotor, connected to the wheel of the vehicle. A set of brake pads hug the rotor. As force is applied to the brake pedal, the brake pads hug the rotor tighter causing more friction. The friction causes the vehicle to slow down. A caliper converts the fluid pressure in the brake lines to the mechanical motion of the pads.
Trouble Guide
High Pitched Squeal • Disc brake pads worn out
Trouble Guide
Grinding • Disc brake pads or shoes worn out Drum Brakes The drum brake system consists of a drum that is connected to the wheel. Inside the drum is a set of brake shoes. As a force is applied to the brake pedal, the brake shoes are forced out causing friction with the drum. This friction causes the vehicle to slow down. A wheel cylinder converts the fluid pressure in the brake lines to mechanical motion of the shoes.
Trouble Guide
Pulsating Brakes • Disc warped • Drum warped Brake Fluid Brake fluid links major braking system components. Brake fluid travels through lines to connect the master cylinder to the calipers in a disc brake system or wheel cylinders in a drum brake system. Brake fluid must be able to flow freely at high and low temperatures. Brake fluid absorbs water and thus should always be kept in sealed containers. Brake fluid fights corrosion, lubricates moving parts, and protects metal, plastic, and rubber components. The most common type of brake fluid is DOT 3, but always refer to the owner’s manual for the specific vehicle. Warning: If brake fluid is spilled on a vehicle’s finish, it will strip paint.
Trouble Guide
Pedal Travels to the Floor • Low brake fluid • Brake fluid leak
Trouble Guide
Spongy Brakes • Air in the brake system
Tech Tip
Air in the Brake System Often when brake components are replaced, air gets into the system. Air, unlike brake fluid, is compressible. When air gets into the system the operator will notice a very spongy and soft brake pedal. If this happens, the system must be bled. Bleeding the air out of the system consists of pushing the air out of a “bleeder” at the caliper or wheel cylinder. Antilock Brakes Antilock brakes can be used with both disc and drum brake systems. In a conventional braking system, the wheels are likely to lockup if the operator applies a large enough force to the brake pedal. During wheel lockup, the operator’s braking distance increases and control of steering decreases. Antilock brake systems reduce wheel lockup. Antilock systems use sensors and computers to monitor wheel speed. If a sensor notices that a wheel is about to lockup, it releases pressure in the caliper or wheel cylinder.
Antilock brake systems
ABS help the vehicle stop faster and the operator maintain control. Some automobiles have antilock brakes on two wheels, while others have antilock brakes on all four wheels. If a vehicle only has two-wheel antilock brakes, the antilock brake system is usually in the rear of the vehicle.
Emergency Brakes Emergency
parking brakes use the same hardware at the wheels to stop the vehicle, but use a different connection mechanism. Instead of using fluid as the connection between the pedal and the brakes, it uses a mechanical cable. This allows one system to work independently of the other. If the vehicle unexpectedly loses brake fluid, the emergency brake would still work. However, the emergency brake only connects to the rear brakes, so braking distance will greatly increase.
Summary
Brake systems use friction to slow and stop a vehicle. The two types of brake systems used today are disc and drum brakes. Disc brakes use rotors, pads, and calipers. Drum brakes use drums, shoes, and wheel cylinders. Antilock brakes assist in preventing wheel lockup and provide the operator with maximum directional control. The parking brake uses a mechanical linkage (cable) instead of a fluid linkage (brake fluid) as a secondary stopping method in emergencies.