Hydraulic Brake - Component Specifics

Component Specifics

(For typical light duty automotive braking systems)

The brake pedal is a simple lever. One end is attached to the framework of the vehicle, a pushrod extends from a point along its length, and the foot pad is at the other end of the lever. The rod either extends to the master cylinder (manual brakes) or to the vacuum booster (power brakes).

In a four-wheel car, the FMVSS Standard 105, 1976; requires the master cylinder is divided internally into two sections, each of which pressurizes a separate hydraulic circuit. Each section supplies pressure to one circuit. Passenger vehicles typically have either a front/rear split brake system or a diagonal split brake system (the master cylinder in a motorcycle or scooter may only pressurize a single unit, which will be the front brake).

A front/rear split system uses one master cylinder section to pressurize the front caliper pistons and the other section to pressurize the rear caliper pistons. A split circuit braking system is now required by law in most countries for safety reasons; if one circuit fails, the other circuit can stop the vehicle.

Diagonal split systems were used initially on American Motors automobiles in the 1967 production year. The right front and left rear are served by one actuating piston while the left front and the right rear are served, exclusively, by a second actuating piston (both pistons pressurize their respective coupled lines from a single foot pedal). If either circuit fails, the other, with at least one front wheel braking (the front brakes provide most of the speed reduction) remains intact to stop the mechanically-damaged vehicle. Just before 1970, diagonally split systems had become universal for automobiles sold in the United States. This system was developed with front wheel drive cars suspension design to maintain better control and stability during a system failure.

The diameter and length of the master cylinder has a significant effect on the performance of the brake system. A larger diameter master cylinder delivers more hydraulic fluid to the caliper pistons, yet requires more brake pedal force and less brake pedal stroke to achieve a given deceleration. A smaller diameter master cylinder has the opposite effect.

A master cylinder may also use differing diameters between the two sections to allow for increased fluid volume to one set of caliper pistons or the other.