Hydraulic System: Description and Operation

Dual Braking Circuit
The basic hydraulic system involves 2 separate and independent primary and secondary circuits which permits a degree of braking should a fault occur in one of the circuits. The primary circuit operates the rear brake calipers and the secondary circuit the front brake calipers.

Fluid Loss Warning System
A brake fluid loss switch is fitted to the master cylinder reservoir filler cap. The switch is wired to a warning light on the vehicle fascia and will illuminate momentarily when ignition is switched on and indicates that the warning circuit is functioning correctly. A hydraulic failure in the system will result in fluid loss, causing the warning light to illuminate.

Pressure Reducing Valve
A Pressure Reducing Valve (PRV), fitted to the RH bulkhead in the engine compartment, maintains the braking balance, see J6322. Pressure to the rear calipers is regulated by the PRV, this valve is of the failure by-pass type allowing full system pressure to the rear brake calipers in the event of a front (secondary) circuit failure.

Servo Unit, Power Brakes
The servo unit provides controlled power assistance to to the brake pedal when pressure is applied. Vacuum is obtained from the depression in the inlet manifold. The vacuum is applied to both sides of a flexing diaphragm and by admitting atmospheric pressure to the rear diaphragm, assistance is obtained. The servo unit is mounted between the brake pedal and master cylinder and is linked to these by push rods. Should a vacuum failure occur, the two push rods will act as a single rod allowing the brakes to function in the normal way, although more effort will be required to operate the brake pedal.

Master Cylinder
A tandem master cylinder, which is assisted by a lightweight compact servo, is fed by a divided fluid reservoir. The rear section supplies fluid for the primary circuit and the front section the secondary circuit.