Parking Brake System: Description and Operation

Parking Brake

Introduction
The parking brake system utilized on the New Range Rover is a new application on Land Rover vehicles. The characteristics of the system are significantly different to the transmission brake based system that is currently fitted to most Land Rover vehicles.

Description
The handbrake lever is a clenched two-shell construction incorporating an automatic cable adjuster. The handbrake 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 en automatic adjuster which eliminates the need for warranty adjustments. The two-shell design allows automatic assembly of the internal components.

The hand brake cable is centrally mounted within the lever assignment 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 handbrake.

Function
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 handbrake cable. This allows the adjuster spring, if required, to remove slack in the handbrake cables. After less then 5 ° 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 or by the dealer. The function of the adjuster is to remove slack in the handbrake 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.

Performance
In order to achieve the required performance targets, the lever ratio is relatively high at 7 25 1. Also, in comparison to Range Rover, 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 25 - 30 mm, in other words in the worst tolerance condition the system can compensate for 25 mm of slack in the cable system. Slack in the system can be caused by both initial tolerance stack-up in the body I parking brake system and actual "stretch" in the system.

Replacement
The handbrake is supplied with a pin in position that rocks the adjuster spring in the fully compressed condition. This allows the handbrake 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 end fitted over the ends of the body tubes, in order to provide location whilst 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 fitment.