Brake Master Cylinder: Description and Operation

Fig. 1 Front & Rear Split Brake System:

(Figure 2) Diagonal Split Master Cylinder:

Front & Rear Split System
When the brake pedal is depressed, both the primary (front brake) and the secondary (rear brake) master cylinder pistons are moved simultaneously to exert hydraulic fluid pressure on their respective systems, Figs. 1 and 2.
If the rear (secondary) brake system fails, initial brake pedal movement will cause the unrestricted secondary piston to bottom in the master cylinder bore. Primary piston movement will displace hydraulic fluid in the primary section of the master cylinder to actuate the front brake system.
If the front (primary) brake system fails, initial brake pedal movement will cause the unrestricted primary piston to bottom out against the secondary piston. Continued downward movement of the brake pedal moves the secondary piston to displace hydraulic fluid in the rear brake system to actuate the rear brakes.

Fig. 3 Diagonally Split Brake System:

Diagonally Split System
This system operates on the same principle as conventional front and rear split systems, using primary and secondary master cylinders which move simultaneously to exert hydraulic pressure on their respective systems. The hydraulic brake lines on this system, however, have been diagonally split front to rear (left front to right rear and right front to left rear) in place of separate lines to the front and rear wheels, Fig. 3.
In the event of a system failure, the remaining non-failed system will do all the braking on one front wheel and one rear wheel, thus maintaining 50% of the total braking force.