Parking Brake System: Description and Operation

Parking Brake

COMPONENT LOCATIONS (PART 1):

COMPONENT LOCATIONS (PART 2):

GENERAL

The parking brake is a manually actuated system that operates drum brakes integrated into the rear brake discs.

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

The parking brake 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.

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 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 or by the dealer. 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.

PERFORMANCE

In order to achieve the required performance targets, the lever ratio is relatively high at 7.25:1. Also, 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 and the parking brake system, and the actual 'stretch' in the system.

REPLACEMENT

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 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.

System Specifications:

SERVICE

The servicing requirements for the parking brake lever and cable system are minimal. However, the parking brake cables remain a serviceable item and will need to be periodically replaced. The cables will always be in tension due to the automatic adjuster and this tension must be released in order to facilitate replacement. The process to achieve this is as follows:
^ Lower parking brake to rest position.
^ Release gaiter from center console and roll back to expose lever assembly.
^ Remove access panel from rear of center console.
^ Pull back equalizer until adjuster spring is fully compressed.
^ Replace pin. A suitably sized pin of adequate strength (preferably steel) may be used.
^ Replace cables.
^ Remove pin. The pin may be removed with the parking brake in any position.
^ Replace gaiter and rear access panel.

WARNING INDICATOR

A switch at the base of the handbrake lever operates the parking brake warning indicator in the instrument cluster. When the handbrake is applied the switch connects an earth to the instrument cluster, which illuminates the parking brake warning lamp. At the beginning of each ignition cycle the instrument cluster performs a 2 second bulb check of the parking brake warning lamp.