Description & Operation
The brake system is a dual circuit type with Electronic Brake Force (EBD) distribution through Dynamic Stability Control/Anti-lock Brake System (DSC/ABS) control. The mechanical brake system comprises:
- Vacuum booster. See Fig 1 .
- Tandem master cylinder with two central valves for DSC operation.
- Brake fluid reservoir with reed contact fluid level switch.
- Vented front discs/Solid rear discs.
- Single piston calipers.
- Hydraulic lines. See Fig 2 .
The front brakes each comprise a hub mounted, single piston caliper assembly and a vented disc. The inboard side of the disc is protected by a mud shield. When hydraulic pressure is supplied to the caliper, the piston extends and forces the inner pad against the disc. The caliper body reacts and slides on the guide pins to bring the outer pad into contact with the disc.
The rear brakes each comprise a hub mounted, single piston caliper assembly and a solid disc. The operation is the same as for the front brakes. Both the left front inboard and right rear inboard brake pad wear is monitored by a sensor attached to the pad by a fly lead. If the brake pad warning has been triggered the sensor and brake pads must be replaced.
The parking brake lever is a clenched two-shell construction incorporating an automatic cable adjuster. See Fig 3 . The parking brake cables are actuated via an equalizer and a cable centrally mounted within the lever, which is in turn attached to one half of the spring loaded adjuster. The design of this hand brake incorporates an automatic adjuster which eliminates the need for adjustment. The two-shell design allows automatic assembly of the internal components. The hand brake cable is centrally mounted within the lever as a significant offset of the cable causes the lever to rotate sideways under the high cable loads required. This construction means that the part of the bracket that supports the lever pivot must be moved outside the lever rather than having the conventional inboard position. The lever is high mounted to suit the COMMAND driving position, on a secondary mounting bracket, which also allows the assembly of necessary components under the parking brake.
When the lever is in the rest position, the adjuster opener holds the adjuster open. In this position, the lever is effectively disconnected from the parking brake cable. This allows the adjuster spring, if required, to remove slack in the parking brake cables. After less than 5 degrees of lever travel and normally before the first tooth is engaged, the adjuster is closed and the cables and hence the parking brakes are actuated. No adjustment of the cables is required during assembly. The function of the adjuster is to remove slack in the parking brake cables and not to provide any adjustment of the parking brake itself. The adjuster spring force is always lower than the brake shoe return spring force.
In order to achieve the required performance targets, the lever ratio is relatively high at 7.25:1. Fine ratchet teeth are employed for the convenience of slighter drivers. The overall performance of the system is totally dependent on the correct adjustment and bedding of the Duo-Servo parking brake. The adjuster travel is 0.98-1.18" (25-30 mm), in other words in the worst tolerance condition the system can compensate for is 0.98" (25 mm) of slack in the cable system. Slack in the system can be caused by both initial tolerance stack up in the body/parking brake system and actual stretch in the system.
The parking brake is supplied with a pin in position that locks the adjuster spring in the fully compressed condition. This allows the parking brake to be raised to the fully up position with the cables connected, in order to facilitate the assembly of the center console. Subsequent to the assembly of the center console, the pin can be removed and the lever lowered, at which point the adjuster will provide the required cable tension. A mounting clip is provided, which is clipped to the equalizer and fitted over the ends of the body tubes, in order to provide location while the cables are fed through the body tubes and into the quick fit connections in the equalizer. This allows a one man operation for cable installation.