The brake pedal assembly acts as nothing more then a mechanical lever armed to apply force to the master cylinder piston. When a driver presses the brake pedal, the master cylinder piston presses against the brake fluid. The force is transmitted throughout the brake system as a hydraulic pressure. This pressure is sent to the individual wheel cylinders, enabling the cylinders to apply the brake system’s components.normally all vehicles have a stop light switch, attached to the brake pedal. Depressing the brake pedal because the vehicles stop light switch to activate the stop lights in the rear of the vehicle.
Master cylinder-
The basic master cylinder consists of a reservoir, reservoirs cover with a gasket, housing, piston, return spring, and a rubber piston cup.
The master cylinder is basically a foot operated hydraulic pump that provides the pressure used in the braking system. A master cylinder has four basic functions.
– It devolves pressure, causing the wheel cylinder piston s to move towards the rotor or the drums
– After the shoes and pads produce a decent amount of friction, the master cylinder helps equalize the pressure required for braking.
– It keeps the system full of fluid as the brake linings wear.
Brake fluid is carried through steel pipes, called the brake lines. Brake lines are constructed of double walled steel tubing that has double lap flares on the end. Steel tubing may crack if it vibrates too much, so rubber brakes hoses are used where flexing action is required. So a flexible brake hose is used between the frame and the calipers of the front wheel. This will allow the wheels to move up and down with suspension and side to side during turns without damaging the brake lines. Rear wheel drive vehicles most often use a junction block wherever a single brake line must feed two brake cylinders. A junction block is a hollow fitting that has one inlet, and more then one outlet.
To make sure the correct amount of brake force is transmitted to the individual wheel brake assemblies, manufactures have to use various types of valves in the brake system
Pressure differential valve–
Is usually located in the combination valve. The combination valve may also hold the proportion valves, and the metering valves. During normal operation, pressure to the primary and secondary brake circuits balances the valve.
Metering valve-
The metering valve is designed to equalize braking action on vehicles that combine front disc and drum brakes. The metering valve functions by preventing the front disc brakes front applying until the rear brakes being to work. This has to happen because disc brakes are fast acting, while drum brakes have spring tension.
Proportioning valve–
This is function to balance brake pressure between the front a rear brakes.proportioning valves are calibrated to a split point and slope (some have these stamped on them) the is the point at which the valve restricts fluid flow to the rear brakes. The slope represents the rate at which brake pressure is applied to the rear brakes.
Height sensing brake proportioning valve-
This is commonly used on light weight trucks and some front wheel drive passenger vehicles. It’s located on the rear cross member, a linkage arm extends from the cross member to the rear axle or rear suspension.when the vehicle is unloaded the linkage partially closes the valve, reducing hydraulic pressure to the rear brakes. Then when the vehicle is loaded, the weight presses the back end of the vehicle down on the springs, and as this happens the linkage also compresses, causing the valve to open. This allows more pressure to the rear brakes, and also allows the vehicle to have the correct front and rear brake ratio, regardless of the weight of the vehicle load.
