The Operation of a Dual Circuit Master Cylinder

A dual circuit, or dual split, master cylinder is a type of master cylinder that uses two different pressure-building sections to operate the front-end and back-end brakes separately. It can also operate diagonally for added safety.

Function

If a regular master cylinder fails or becomes defective, the hydraulic braking operation essentially fails entirely. Assigning a circuit of the master cylinder to a pair of brakes allows the car to stop should the other circuit (and the other brake pair) fail.

Structure of the Dual Split Master Cylinder

Two chambers of the master cylinder are divided and assigned one end of the car's brakes. Typically, the "nose-end", which points to the front of your car, operates the rear brakes, while the (opposite) pushrod-end manages the front brakes. Some manufacturers, like General Motors, match the nose-end of the master cylinder with the front brakes and the pushrod-end with the rear brakes.

Diagonal Split Function

Because up to 90 percent of the force during braking is absorbed by the front brakes, manufacturers wanted to allow at least one of the front brakes to remain operational should one part of the circuit fail. Therefore, each circuit manages one front-end brake and one rear-end brake and cross each other in an X-type design.