Slack Adjusters
The slack adjuster is the link between a brake chamber or actuator and the S-Cam brake camshaft. Its arm is fastened to the pushrod with a yoke and its spline is installed on the foundation brake camshaft. It transforms and multiplies the force developed by the chamber into a torque which applies the brakes via the brake camshaft.
Manual Slack Adjusters
To compensate for the gradual wear on the brake block lining, slack adjusters are equipped with an adjusting mechanism, which provides a means of adjusting for brake lining wear. Slack adjuster models are designated by a number that represents its maximum torque rating (e.g. a type 20 unit is rated for a maximum of 20,000 inch-pounds of torque). Slack adjusters are available in various arm configurations, lengths and spline types.
The entire slack adjuster operates as a unit, rotating as a lever with the brake camshaft as the brakes are applied or released. The most efficient braking action is obtained when the slack adjuster arm travel is approximately 90 degrees and in the recommended range of the chamber. Therefore, it is important that brake adjustments are made as often as necessary.
Automatic Slack Adjusters
Automatic slack adjusters perform the same function as the standard unit, except that it automatically adjusts for lining wear. The Bendix “sure stroke” unique design monitors brake lining to brake drum clearance, thus eliminating the possibility of over adjustment. The automatic slack adjuster does not require periodic manual adjustment, however, the unit does provide for manual adjustment. All Bendix slack adjusters incorporate a grease fitting and/or a tapped hole for a lube fitting.
Ideal ASA-5™ Slack Adjuster Installation
The brake chamber push rod and arm of the slack adjuster should reach approximately 90 degrees at 1/2 the available stroke (mid-stroke) of the chamber. The chart to the right shows the ASA-5™ slack adjuster installation tolerance.
Air Chamber
Move the air chamber from side to side to check that the caliper moves freely on the slide pins. When the caliper does not move freely, inspect the slide pins, slide pin bushings and slide pin retainers for wear or damage. Replace components when necessary. Refer to Section 10 and Section 4.
Linings
When the linings wear, the caliper slides in along the slide pins. To check for lining wear, check the position of the caliper inboard bosses on the slide pins. Figure 13.6. If the bosses are within 1/4-inch (6.4 mm) of the ends of the pins, remove the wheels and tires and inspect the linings. If the bosses are within 1/8-inch (3.2 mm) of the ends of the pins, replace the linings. Refer to Section 10.
Major Inspections
When you reline the brakes, or at least one time a year, perform the following inspection:
1. Inspect the automatic slack adjuster and brakes as previously described in “Minor Inspections.” Perform minor inspections before you do any other maintenance or reline procedures.
2. Perform all the procedures, inspections and measurements described in Section 10.
3. Lubricate the automatic slack adjuster and the caliper.
4. Adjust the brakes as described in Section 11