Brakes (Hydraulic system): Description and operation

HYDRAULIC SYSTEM

The hydraulic system operates the brakes in response to brake pedal movement and, on ABS variants, operation of the ABS modulator.

To reduce operating noise on vehicles with ABS, sleeving is installed on some of the brake pipes in the engine compartment and the pipes are located in sprung pipe clips.

For normal brake operation, brake pedal movement is assisted by the brake servo assembly and transmitted to the master cylinder assembly. The master cylinder assembly converts brake pedal movement to hydraulic pressure. Primary and secondary brake pipe circuits supply the hydraulic pressure to the brakes: the primary circuit supplies the front left and rear right brakes; the secondary circuit supplies the front right and rear left brakes. A Pressure Conscious Reducing Valve (PCRV) regulates the pressure to the rear brakes to give front/rear differential braking.

A red, brake warning lamp in the instrument pack illuminates if the fluid level in the hydraulic system falls to an unsafe level.

Vacuum for the brake servo assembly is obtained from the engine inlet manifold (petrol models) or a vacuum pump (diesel models) through a vacuum line and non return valve.

Hydraulic system schematic - non ABS

1. Servo/Master cylinder assembly
2. Brake pedal
3. Pressure conscious reducing valve
4. Front brake
5. Rear brake