The service brakes are the drum and shoe type. The
chamber (power unit) mounted on the brake backing
brakes on the rear axle are single wedge actuated
plate. The brakes have automatically adjusting
and the brakes on the front axle are dual wedge
plungers that ensure the brakes are properly
actuated. Each wedge is actuated by an air brake
adjusted to compensate for brake lining wear.
To ensure proper operation of service brakes,
perform Preventive Maintenance Checks and
The brake actuator (expander unit) is adjusted at the
minimum dimension by the manufacturer. This
Brakes should be cleaned, inspected, lubricated, and
dimension varies with respect to the brake diameter.
adjusted each time the hubs are removed.
When changing linings (after turning down the
drums and linings), turn the adjusting screw to obtain
During a major overhaul, the following parts should
a clearance of 0.006 in. 0.0015 in. ( 0 .152 mm
be carefully checked and replaced with genuine
0.04 mm) between brake shoe and drum. Do not
replacement parts as required.
block the screw. Check the sealing of the boots.
Check the backing plates for distortion,
looseness, and sheared rivets.
Slowly operate the brake system using the pedal
operated valve. Look through the holes to see that
the shoes move against the drums. After releasing
the pedal, the brake shoes should return instantly to
Check the brake shoes for wear at the anchor
the original position.
Shoe return springs should be replaced at the
time of overhaul.
In the event of wear or oil impregnation, always
change the linings on both sides of the axle. Never
Check the brake linings for grease saturation,
replace the linings on one side only.
wear, and loose rivets or bolts.
Check the drums for cracks, scoring, or other
Admissible machining of the brake drum to remove
scoring is 0.06 in. (1.54 mm) radially. Thus, the
maximum allowable inside diameter of the drum after
machining is 16.26 in. (413.08 mm) or .75% of the
nominal diameter of 16.14 in. (410 mm).