Hydraulic Unit

Independent of master cylinder pressure, hydraulic unit adjusts brake fluid pressure to wheel cylinders during regulation. Brake fluid pressure from hydraulic unit cannot exceed master cylinder pressure. Three 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 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 electrical connector of hydraulic unit. A diode is soldered in socket. Hydraulic unit is connected to ground by cable.