Brakes and Traction Control: Description and Operation

NOTE: It should be noted that the two systems (AP and Lucas Girling) are not interchangeable on a component by component basis but must be changed as a complete package, ie, servo, master cylinder, brake pipes and pedal box.

DESCRIPTION AND OPERATION

Lucas Girling Brake System:

Later 1987 models are fitted with an uprated Lucas Girling type LSC 115 servo and 25.4mm AS/AS master cylinder plus associated brake pipes and pedal box assembly.

The brake failure warning system on the Lucas Girling type is a Fluid Level Warning Indicator (FWLI) which is incorporated into the fluid reservoir cap and is activated when fluid loss in the reservoir is sufficient so that the float in the switch drops and in turn illuminates a brake failure warning light in the instrument panel.

The hydraulic braking system fitted to Range Rovers is the dual line type, incorporating primary and secondary hydraulic circuits.

NOTE: References made to primary or secondary do not imply main service brakes or emergency brakes but denote hydraulic line identification.

The brake pedal is connected to a vacuum assisted mechanical servo which in turn operates a tandem master cylinder. The front disc brake calipers each house four pistons. The upper pistons are fed by the primary hydraulic circuit. The lower pistons by the secondary hydraulic circuit. The rear disc brake calipers each house two pistons. These are fed by the secondary hydraulic circuit via a pressure reducing valve.

A brake fluid level switch is incorporated into the reservoir cap assembly, the switch having detected either low or sudden fluid loss will immediately illuminate a warning light in the instrument panel.

The brake fluid reservoir is divided, the section closest to the servo feeds the primary circuit and the section furthest from the servo feeds the secondary circuit. Under normal operating conditions both the primary and secondary circuits operate simultaneously on brake pedal application. In the event of a failure in the primary circuit the secondary circuit will still function and operate front and rear calipers. Alternatively, if the secondary circuit fails the primary circuit will still function and operate the lower pistons in the front calipers, allowances should be made and vehicle speed adjusted accordingly to allow for the lack of full braking efficiency.

If the servo should fail, both hydraulic circuits will still function but would require greater pedal effort due to the lack of vacuum assistance.

The hand operated parking brake acts on a brake drum at the rear of the transfer gearbox and is completely independent of the hydraulic circuits.

Brake pad wear sensors are incorporated in the front and rear right hand side inboard brake pads. The sensors will illuminate a brake pad wear warning light in the instrument panel, when pad thickness has been reduced to approximately 3mm (0.118 in).

Primary/Secondary Hydraulic Circuit Primary/Secondary Hydraulic Circuit:

Primary/Secondary Hydraulic Circuit

Brake Hydraulic Circuit:

Hoses
1. Front left hand flexible hoses.
2. Front right hand flexible hoses.
3. Intermediate flexible hose.

Pipes
4. Feed to front left hand hose connector.
5. Feed to front right hand hose connector.
6. Feed to front left hand caliper.
7. Feed to front right hand caliper.
8. Feed to rear left hand caliper.
9. Feed to rear right hand caliper.
10. Feed to two way connector.
11. Feed to intermediate hose.
12. Two way connector.
13. Three way connector.
14. Pressure reducing valve.