Brake System Operation
Vehicle brake system operation begins with the driver and the application of the brake pedal. Brakes slow and stop a vehicle by transforming vehicle motion into heat energy. The amount of heat produced is proportional to the vehicle speed and driver foot pressure on the brake pedal. Fast vehicle speeds and quick stops produce more heat. The brake system is comprised of many sub-systems. Stopping a vehicle requires that all brake sub-systems work together. The first system that is activated during a stop is the Apply system.
The driver depresses the brake pedal, operating the brake pedal linkage. The linkage connects the pedal to the Power Brake Booster or Master Cylinder. Located near the brake pedal is the stop lamp switch. Proper adjustment of this switch is necessary to illuminate the brake lights.
Power Brake Booster
Most vehicles are equipped with a Power Brake Booster. The Booster increases brake pedal force (Boost System). The booster links the brake pedal Apply system to the Master Cylinder Assembly.
Master Cylinder Assembly
Today's high performance hydraulic brake master cylinders are the result of years of component and design improvements. Applying brake pedal force moves pistons in the master cylinder, forcing pressurized brake fluid out through steel brake lines and rubber flexible brake hoses. Master Cylinders are single-bore-dual hydraulic channels that allow one channel to operate should the other channel fail. Brake fluid from the Master Cylinder flows through steel brake lines and flexible reinforced rubber hoses.
Extremely important and often overlooked, brake fluid is the medium that transmits energy from pressure on the brake pedal to the caliper and wheel cylinder pistons. All brake fluids eventually wear out. Branded brake fluid is manufactured with corrosion inhibitors to help protect the brake system. Corrosion can pit the bores of the master cylinder, calipers, wheel cylinders, and ABS components. Some manufactures recommend flushing the brake system every 2 years or 24 thousand miles. Consult your owner's manual for your vehicle's brake fluid type and service recommendation. Brake fluid absorbs moisture and can damage paint. Use caution when handling brake fluid.
Hoses & Steel
Brake hoses and steel lines transmit brake fluid pressure produced in the master cylinder. From the steel lines, brake fluid pressure is channeled through Balance Control Systems. All features included in original equipment brake hoses such as brackets, grommets, molded plastic guards, or wire clips are found on most brake hoses. Double wall steel brake lines are coated to resist rust and corrosion. All hoses and steel lines meet or exceed Department of Transportation (DOT), Society of Automotive Engineers (SAE), and Federal Motor Vehicle Safety Standard (FMVSS) specifications. The resulting benefits are optimal protection, service life and safety.
Balance Control - Warning system
Balance control systems typically consist of a combination valve located on or near the master cylinder or in the steel lines between calipers and wheel cylinders. The balance control system ensures that brakes apply quickly, simultaneously, and at a balanced pressure for safest operation. An instrument panel lamp (red brake warning light) signals the driver of a hydraulic system failure, parking brake application, or when low brake fluid levels occur. On many newer vehicles, worn out friction material will also illuminate the red brake warning light.
The brake calipers are large hydraulic clamps. Calipers have one or more pistons that move outward with increased brake fluid pressure, forcing the friction material (brake pads) to contact the rotor surface. When the driver releases foot pressure from the brake pedal, the caliper piston seal retracts, pulling the brake pads off of the rotor surface. Caliper pistons are self-adjusting, the caliper piston seal maintains proper pad-to-rotor contact as the pads wear. Caliper integrity is vital to the function of the brake system. Seals, o-rings, slides, and lubrication become compromised as a result of exposure to road grit, corrosion, deposits, heat and contaminated brake fluid. Wheel cylinders are used with drum brake systems. Brake fluid piped to wheel cylinders provides hydraulic pressure to the movable pistons within each cylinder. This pressure forces the brake shoes into the drums. When the driver releases foot pedal pressure, large return springs (hardware) secured to the brake shoes, forces the wheel cylinder pistons back to their resting position.
Hardware consists of a variety of parts designed to assist in restoring your brake system to "Like New Performance". Caliper anti-rattle clips, seals, pins, and dust boots; along with drum shoe return springs, hold down springs, and adjuster assemblies, help to maintain consistent, balanced braking.
Brake Pads and Shoes
Friction material includes disc brake pads and drum brake shoes. At each wheel, pressurized brake fluid moves pistons. Pistons press brake friction material against a rotating rotor or drum, slowing the vehicle. Caliper pistons move brake pads, while wheel cylinder pistons move brake shoes.
Rotor Assembly - Rear Drum Brake Assembly
Late model brake systems on most cars and light trucks utilize disc brake rotors on the front, and brake shoe drums on the rear. Rotors and drums are both very important to the effectiveness of vehicle braking. Our technical skills and manufacturing facilities enable us to produce nearly every brake drum and rotor configuration on the road today.
Anti-Lock Braking System (ABS)
ABS systems are add-on devices to conventional base brake systems. ABS allows the driver to maintain steering control of the vehicle while in hard braking situations. Computerized ABS is designed to keep the wheels from locking as the brakes are applied. A locked wheel provides very little or no directional control. Drivers should maintain firm brake pressure on the brake pedal of ABS equipped vehicles, because pumping the brakes only extends the stopping distance. Drivers may experience a pulsation in the brake pedal, or pedal kick back during an ABS stop. This is normal and not to be confused with a conventional brake pedal pulsation. Major components of the anti-lock brake system consist of a computer module, hydraulic assembly, speed sensor(s), wiring, and the amber ABS brake warning light.
The electronic brake control module monitors the ABS system during start up and during vehicle operation. This initial test is referred to as a "self test". During the self-test the amber light may remain on for 3 to 5 seconds. The light is turned off if the system passes the self-test. Should the module detect an error, it will illuminate the amber ABS warning light and disable the antilock function. While you are driving the vehicle, the module monitors wheel speed data from each wheel speed sensor, and controls the hydraulic assembly during an ABS stop.
The hydraulic assembly is a series of electro-hydraulic valves that regulate individual brake line pressure at the wheels or axle. Modulation can occur as many as 15 times per second. This action helps prevent wheel lock up and maintains vehicle control.
Wheel Speed Sensor
Wheel speed sensors are located individually at each wheel or axle. These sensors generate a signal that changes with wheel speed. Imagine one wheel on dry pavement and one wheel on ice. A speed sensor signal that suddenly drops off indicates that one or more wheels are approaching lock up. This information is being monitored by the computer, which in turn commands the hydraulic modulator to regulate line pressure at the affected wheels. When accessible during normal brake service, wheel speed sensors should be cleaned and air gap checked.
Bearings and Seals
Wheel bearings should be inspected and lubricated periodically. Worn wheel bearings, which can cause faulty steering as well as erratic braking, should be replaced.