Brake Master Cylinder: Description and Operation

Operation
Operating the brake pedal will move pistons (1 and 4) forward. Primary cups (2 and 5) slide over compensation bores (3 and 6). Now there is equal pressure in chambers A and B.

Diagonal Dual Circuit System
Chamber A serves right front and left rear. Chamber B serves left front and right rear. If a brake circuit fails, the brake pedal travel will increase considerably.

If the second brake circuit fails, the pressure building up in chamber A will act on piston (1) to move piston (4) in the pressureless chamber B against the tandem brake master cylinder housing and restore function of the first brake circuit.

If the first circuit fails, piston (1) will be pressed against spring cap (7) in pressureless chamber A and the second brake circuit will function normally via chamber B.