Figure 12-37.-Checking lining wear (method No. 1).
lining is worn to a thickness of one-sixteenth inch or
less, the entire set of linings must be replaced. Figure
12-38 illustrates the normal position of the automatic
adjusting pin (protruding out of the adjusting pin nut).
Emergency System Contamination Check
Check the emergency system for contamination.
Remove the plug from the unused pneumatic pressure
port on the brake assembly. Position a clean, white cloth
adjacent to the opening, and slowly pull the emergency
brake control handle. Allow airflow through the system
for approximately 5 seconds. There should be no
evidence of combustible contaminants on the cloth. If
the system is contaminated, the emergency brake
pneumatic lines from the brake control valve to the
brake assembly must be flushed with a suitable solvent.
Purge for a minimum of 15 minutes with heated
There are two general methods of bleeding brake
systemsbleeding from top downward (top-down
method) and bleeding from the bottom upward
(bottom-up method). The method used generally
depends on the type and design of the brake system to
be bled. In some instances it may depend on the bleeding
equipment available. A general description of each
method is presented in the following paragraphs.
TOP-DOWN METHOD.In using the top-down
method, the air is expelled from the system through one
of the bleeder valves provided on the brake assembly.
See figure 12-39. A bleeder hose is attached to the
Brake fluid port
Adjusting pin nut
Adjusting pin grip
Piston return spring
Figure 12-38.Normal position of automatic adjusting pin.
Figure 12-39.Bleeding brake system (top-down method).