AP System

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

AP Type Brake System:

Early 1987 Range Rover vehicles were fitted during manufacture with an Automotive Products (AP) master cylinder and servo assembly, together with associated brake pipes and pedal box assembly.

The brake failure warning system on the AP type master cylinder is a Pressure Differential Warning Actuator (PDWA) switch, which is activated when the shuttle valve moves along its bore due to pressure differential in either the primary or secondary circuits caused by fluid loss or seal failure. The result of the shuttle valve movement is to illuminate a brake failure warning light in the instrument panel.

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

NOTE: References made to primary and 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 and these are fed by the secondary hydraulic circuit via a pressure reducing valve.

A brake failure switch incorporated in the master cylinder will illuminate a panel warning light if a failure occurs in either the primary or secondary hydraulic circuits.

The brake fluid reservoir is divided, the front section (section closest to the servo) feeds the primary circuit and the rear section feeds the secondary circuit. Under normal operating conditions both the primary and secondary hydraulic 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 upper pistons in the front calipers.

If the servo should fail, both hydraulic circuits will still function but would require greater pedal pressure.

The hand-operated parking brake is completely independent of the hydraulic circuits.

Brake pad wear sensors are incorporated into the front right and rear left 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).

Brake Hydraulic Circuits:

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. Feed to pressure reducing valve.
13. Brake failure warning switch.