Automatic Slack Adjusters; Parking Brake System - Mack Granite GU Series Operator's Handbook Manual

160 OPERATION
When slowing for a stop, leave the clutch engaged for as long as possible to
use the braking effect of the engine. When forward speed has dropped to a
little above idling speed, push clutch pedal in and brake to a complete stop.

Automatic Slack Adjusters

Automatic slack adjusters are designed to automatically maintain proper brake
chamber pushrod travel and compensate for brake lining wear during normal
use. Manual adjustment of an automatic slack adjuster should never be
performed except when performing brake or wheel service (such as backing
off the brake shoes for wheel removal, brake shoe relining/replacement, brake
drum reconditioning, etc.).
When pushrod travel exceeds specifications (as given in the "BRAKE
ADJUSTMENT" section of the Maintenance and Lubrication Manual, on a
vehicle equipped with automatic slack adjusters, a mechanical problem with
the slack adjuster, brake components or improper installation of the slack
adjuster is indicated. If brakes are found to be out of adjustment, the vehicle
must be taken to the nearest repair facility to have the problem investigated
and corrected.
DANGER
Automatic slack adjusters should not be manually adjusted in an effort to correct
excessive pushrod stroke, because this condition indicates that a problem exists
with the automatic adjuster, with the installation of the adjuster, or with related
foundation brake components, which manual adjustment will not fix. Manual
adjustment of automatic slack adjusters is a dangerous practice that could have
serious consequences, because it gives the operator a false sense of security
about the effectiveness of the brakes, which are likely to go out of adjustment
again soon.

Parking Brake System

Spring-type parking brakes are standard on all single and tandem rear axles.
The spring brake system consists of an air cylinder with heavy springs, which
is integrated with the spring brake air chamber. When there is no pressure in
the air chamber, the springs expand (causing a brake application). When air
pressure is applied to the air chamber, the springs are compressed (releasing
the brakes).