Parking Brake System: Description and Operation
Parking Brake
COMPONENT LOCATION
OVERVIEW
The parking brake is a manually actuated system that operates brake shoes located in the rear brake discs. The inside center of the rear brake disc is manufactured to form the brake drum.
BRAKE SHOE ASSEMBLY
The brake shoes are mounted horizontally on an integral brake dust shield and backplate, and form an upper trailing and lower leading brake shoe type system. Retaining pins pass through holes in the dust shield and corresponding holes in each brake shoe bracket. Each pin is secured to the brake shoe with a retaining clip. The retaining pins allow movement of the brake shoe toward the drum surface during parking brake operation, but prevent sideways movement of the brake shoe away from the dust shield.
An expander unit and manual adjuster are located along the horizontal axis of the dust shield. The expander unit is positioned at the front of the dust shield and forms the location for the leading and trailing ends of the brake shoe brackets. The manual adjuster is mounted at the rear of the dust shield and forms the location and fulcrum point for the opposite ends of the brake shoe brackets.
The manual adjuster provides the means to adjust the brake shoe lining to drum clearance for maintenance purposes. Access to the manual adjuster knurled wheel is through a formed hole in the front of the brake disc. Adjustment is required if the brake shoes or discs are renewed. A bedding-in procedure must also be performed to make sure the drum brakes operate satisfactorily. For additional information, refer to Parking Brake Shoes Bedding-In Procedures
The corresponding ends of both the upper and lower brake shoe brackets are maintained in contact with the expander unit and manual adjuster by 2 return springs. The return springs are located between the ends of each upper and lower brake shoe and attach to holes formed in the brake shoe brackets. The return springs pull the brake shoes away from the drum when the parking brake is released.
PARKING BRAKE LEVER
The parking brake lever is located in the floor console between the driver and passenger seats, and comprises a toothed quadrant, pawl and press-button release mechanism. A single cable with a formed threaded rod-end connects the quadrant to the equalizer unit, and is secured with either a locknut or a locking washer and nut.
The threaded rod allows adjustments to the parking brake cable tension and parking brake lever travel to be performed for maintenance purposes. For additional information, refer to Parking Brake Cable Adjustment Adjustments
The parking brake cable is routed from the parking brake lever equalizer, and along the chassis to the rear parking brake expander unit. The parking brake cable protrudes through the brake dust shield, and is formed with a nipple that connects to the expander unit. The opposite ends of each Left-Hand (LH) and Right-Hand (RH) parking brake cable are formed with a nipple that connect to the equalizer unit. The equalizer unit makes sure the LH and RH parking brake assemblies operate simultaneously when the parking brake is applied.
A microswitch is located on the base of the parking brake lever. The microswitch operates the parking brake warning indicator lamp located in the instrument cluster, when the parking brake is applied. For additional information, refer to Instrument Cluster Initial Inspection and Diagnostic Overview
PRINCIPLES OF OPERATION
As the parking brake lever is applied, the toothed quadrant rotates and pulls on the threaded rod and cable equalizer. The equalizer pulls the 2 parking brake cables and operates the 2 expander units simultaneously. Movement of the expander unit causes the upper and lower brake shoes to pivot against the manual adjuster fulcrum, and the brake shoes contact the brake drum against the tension of the 2 return springs.
As the parking brake lever quadrant rotates, the teeth on the pawl engage with corresponding teeth on the quadrant. In the applied position, the pawl teeth are held under spring tension against the quadrant teeth to prevent the lever from disengaging.
With the parking brake applied and the ignition in power mode 6 (ignition), the microswitch connects a ground to the instrument cluster and illuminates the parking brake warning indicator lamp. For additional information, refer to Instrument Cluster Initial Inspection and Diagnostic Overview
When the parking brake lever press-button is pressed and the lever moved to release the parking brake, the pawl teeth are raised clear from the quadrant teeth. As the parking brake lever is lowered, the parking brake cable closes the expander unit and the brake shoes are immediately moved away from the brake drum by the 2 return springs.
As the parking brake lever reaches the fully released position, the microswitch is opened to disconnect the circuit to the instrument cluster. With the parking brake released, the parking brake warning indicator lamp is extinguished.