Hydraulic Unit
Independent of master cylinder pressure, hydraulic unit will compensate brake fluid pressure to wheel cylinders during regulation. Pressure increase above master cylinder pressure is not possible.
The 3 hydraulic unit solenoid valves control left front, right front and rear brakes. By activating valves with current of varying amperage, brake fluid pressure in individual calipers may be increased, held or decreased.
In pressure "build-up" stage, pressure increases by opening intake valve to pressure supplied by master cylinder. In pressure "holding" stage, which precedes "reduction" stage, pressure from hydraulic unit to wheels is constant. Output and input valves in solenoid valve are closed.
During pressure "reduction" stage, brake fluid flows from reservoir to return pump. To maintain fluid volume, pump returns fluid to main cylinder against prevailing pressure.
To dampen delivery noise, each circuit has a silencer. Relays for solenoid valves and return pump are on 12-pole socket of hydraulic unit. A diode is soldered in socket. Hydraulic unit is connected to ground by cable.