How Brake Systems and Components Work

Brake systems are designed to slow the vehicles wheel movement through friction. There are primarily two brake systems, ABS and non ABS (anti-lock brake system). Both systems work on basic hydraulics and utilize a brake master cylinder (connected to the brake pedal in the car) that supplies brake fluid pressure to the front brake calipers and rear wheel cylinder or brake calipers if so equipped.  The brake system requires hydraulic force that is many times greater than the force applied by the foot. This added hydraulic force is achieved by leverage multiplication. Varying the relative location of the brake master cylinder rod pivot as it relates to the lever can change the multiplying force.

Power brake systems utilize either vacuum (vacuum assist) or power steering (hydro-boost) to multiply the force without added pedal effort. In the hydraulic force multiplication method, the force, which is applied at one point, is transmitted by incompressible brake fluid to another point. This basic system consists of two pistons (master cylinder and wheel caliper or cylinder), which are filled with brake fluid and are connected by a brake line of any length or shape. When the brake pedal is forced down brake fluid from the master cylinder is transferred to the brake caliper piston, pressurized fluid is transmitted through the brake caliper to the brake pads or shoes, which are mounted to the brake caliper or wheel cylinder.

Typical Non ABS Brake System

A major problem to the brake system is a brake fluid leak, if there is a slow leak in the system it will affect the brake master cylinder by allowing air into the system creating a low pedal and eventual brake operation failure. If a large brake fluid leak is present, fluid escapes, leading to a major brake failure on one half of the system (front or rear). A master cylinder has a built in safety device, two separate hydraulic systems a primary and secondary, with separate reservoirs separating front and rear brake operation. In case of front or rear brake operation failure, one system will still be present.

Common Problems and Fixes

Today’s brake systems are reliable and easy to maintain, most systems are designed for easy service and brake pad replacement. If the brake pedal becomes hard to push, there can be a possibility of a broken vacuum supply line or a failed power brake booster. It is also very important to use the correct type of brake fluid; otherwise the brake system can malfunction. This can lead to problems such as spongy feeling pedal and the brake pedal travel becoming excessive. Only the highest quality brake fluid must be used in a brake system and must never be reused and must always be discarded immediately after the fluid storage container is opened to avoid moisture contamination. When adding brake fluid to the master cylinder care must be taken make sure brake fluid is not spilled on the paint of the car, brake fluid is very corrosive and will destroy the paint.

Squealing brakes is an indication of a problem with the brake system. Most of the time a squealing noise can be a warning that the brake pads are worn down and need to be replaced. Other causes can be overheated brake pads or rotors. Sometimes rust can get impregnated on the brake lining material and cause grumbling or squeaking noises. When cleaning brake components prior to service precautions must be taken. Most brake systems contain microscopic fibers that are extremely hazardous to your health. While cleaning with brake system cleaner there is an increased chance of inhaling these fibers that accumulate on the brake components. Cleaning should be done in a well ventilated area, use an air filter respirator if possible for best results.

When the ABS system detects a problem a fault code is stored in the ABS system control unit. When an error occurs the ABS warning light located on the dashboard flashes or stays on steadily. The ABS computer stores a diagnostic code until the malfunction has been repaired. To retrieve ABS trouble codes on older vehicles can be tricky because of the variation of retrieval methods; in this case a car repair manual is needed. On newer vehicles a diagnostic information connector is located under the dash on the driver’s side; a trouble code scanner can be attached to retrieve ABS codes similar to engine trouble codes.

After the problem has been repaired codes should erase automatically with no procedure from the scan tool in most cases. (Real time system) when the vehicle has been moved about 6 feet and the brake pedal has been pressed for five seconds the codes should clear. When repairs have been completed the ABS, MIL (malfunction indicator lamp) should not be illuminated, if the ABS light remains on there is still a problem, re-scan the ABS computer for further repairs.

Basic Maintenance

It is important to inspect your brake system periodically. Check the level of brake fluid and the thickness of the brake pads or shoes. Before checking the brake fluid level, the cover of the master cylinder must be wiped off so no foreign material can fall inside the reservoir. The brake pads and brake shoes should be periodically inspected for the amount of wear the brake pad has endured and replace as needed. ABS brake systems apply more wear and tear to the brake fluid and can wear brake fluid down chemically. Be sure to flush your brake system with manufacturer recommended brake fluid (DOT 3 or 4) when brake service is performed to ensure proper operation of the ABS brake system in your car.

The ABS brake system is a computerized wheel speed system that can detect when one or more of the wheels is not rotating as fast as the other wheels and will dump brake pressure to those wheels until the wheel (or wheels) can maintain equal rotation. ABS brake systems utilize a series of wheel speed sensors, a brake control module and a main ABS control unit. The ABS control unit controls and monitors the ABS brake system. These brake components transfer evenly dispersed brake fluid pressure to the brake pads and shoes and keep the vehicle under control.

Related Information

Brake Fade: Brake fade is a condition that occurs when the brakes on the vehicle stop working even though there is good pedal and no obvious problems with the brake system. This condition can present itself when the brake system is overheated. When friction is applied to a rotating mass (brake rotor or drum) the energy is transferred into heat, when the brake rotor is over heated it cannot absorb any additional heat. This will cause the brakes to fail no matter how hard the brake pedal is applied. This condition can occur when braking down long grades and in high performance driving applications where repeated acceleration and braking occurs over a short period of time.

Brake System Maintenance and Inspection: Brake system maintenance is crucial. To keep your vehicles brake system serviced correctly flush your brake fluid every 25,000 to 35,000 miles. Inspect brake fluid, master cylinder, pads, flex hoses and shoes for fluid leaks regularly. When replacing brake system components always use top quality OEM (original equipment manufacturer) brake parts. Many inexpensive brake parts will, squeak, grumble, need replacement sooner and generally not perform as well.

Brake Proportioning or Combination Valve: The proportioning or combination valve is located in line with the front and rear brakes. This valve is used to monitor the brake system pressure from front to rear and warn you if a fluid pressure drop is detected. When a system failure is detected a brake warning light is illuminated on the instrument cluster.

Emergency Brake: A car emergency brake performs two operations, it helps hold the car when parked on a hill, plus it can help stop the vehicle if the conventional brake system has failed. Inspect your emergency brake operation periodically to ensure proper operation as part of a normal brake replacement and have the service technician inspect the emergency brake system for wear and replace worn components as needed.

Brake Components

Power Brake Booster

A power brake booster utilizes engine vacuum to help pressurize the hydraulic system in the car when the brake pedal is depressed.



Brake Pad Set

Semi metallic brake pads are generally made with copper, brass, and steel wool shavings held together in a resin. Ceramic based pads are also available for high performance applications.


Rear Brake Caliper

Brake calipers provide hydraulic pressure to the brake pads and apply friction to the brake rotor to slow the vehicle.



Brake Master Cylinder

A brake master cylinder provides hydraulic pressure to the wheel cylinders and calipers.



Brake Shoe Set

The rear brake shoes are actuated by wheel cylinders that force the brake shoes against the brake drum with hydraulic pressure from the master cylinder.



Wheel Cylinder

Pressure from the brake system is applied to the brake cylinders forcing the brake shoes against the brake drum.



If further assistance is needed, our certified car repair technicians are ready to answer your car questions.