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brake-parking-action.jpg | Hits: 6566 | Posted on: 1/13/06 | View original size (78.25 KB)

Parking Brake Action
IF THE IMAGE IS TOO SMALL, click it.
The "FRONT" label at the bottom is wrong for fullsize trucks, whose parking brake lever is always to the REAR.

The basic components of the rear parking brake are shown in the LEFT pane. (The RIGHT pane only applies to pre-'92 trucks.) A cable from the foot pedal or parking brake lever enters through a hole in the backing plate. It is attached to the end of the lever arm. The other end of the lever is attached to a pivot point on the primary shoe. There is a connecting link between the lever and the secondary shoe. Finally, there is a cable return spring (and rattle preventer) at the secondary shoe end of the connecting link.

When the parking brakes are applied, the lever pivots at the pivot point on the primary shoe. Because of the connecting link between the lever and the secondary shoe, the shoes move apart as the lever is activated. The pivot point moves one way, and the connecting link the other. This pushes the shoes tight against the drum and holds the vehicle as long as tension is maintained.

When the parking brake is released the primary and secondary return springs return the shoes to their normal position. The cable return spring pushes the connecting link back against the lever. The movement of the lever takes up any slack in the parking brake cable.

This is just one of several systems for activating the parking brakes. Other systems use a cam-type lever located directly between the primary and secondary shoes in the vicinity of the anchor pin.

In most Ford light trucks, the parking brakes are activated by a foot pedal. However, some motor homes and step vans use an Orscheln lever in place of the foot pedal.

The major service concern occurs when the components fail to retract properly. This may result in brake drag, overheating and excessive lining wear.

Proper parking brake cable tension is essential for good performance, and clean/greased drum brake hardware is critical to tension adjustment. The old way of adjusting this tension was to release the parking brake and tighten the cable manually until the brakes were just about to engage (assuming the drum mechanisms are working properly). A better way is to fully apply the parking brake and check the tension of the cable. There are two ways to do this: Using a tension gauge, or observing the "bent pin" automatic adjuster (pre-'92 ONLY).

If you use a tension gauge, check the appropriate service manual for the proper tension. If you don't have a tension gauge, you can make a visual check of the "bent pin" connection (pre-'92) at the adjusting point in the parking brake cable. The "bent pin" is attached to the cable from the foot pedal by the coupling cap. The pin turns around a pivot in the tension limiter housing. The open end of the pin has a hook, as shown in the inset. This hook prevents the pin from pulling around the pivot point completely during its service life.
Apply the parking brake, making sure that the pedal is at full travel. Slightly tighten the equalizer nut. If the nail doesn't pull, the tension is not sufficient. Tightening the equalizer nut until the nail does pull will set the correct tension. Follow the instructions in the appropriate service manual.

See also:
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