TM 9-2330-294-14
Table 4-4. Troubleshooting Air System Continued
MALFUNCTION
TEST OR INSPECTION
CORRECTIVE ACTION
18. BRAKES WILL NOT RELEASE ON SINGLE WHEEL Continued
Step 2. Check to see if the brake lining is frozen to drum.
Expose brakes to warmth.
Step 3. Check lining to drum clearance. If no clearance exists, manually compress fail-safe or ad-
just brakes (pars 4-30b ) until clearance is obtained, then pull hub and dmm (para 4-60).
Visually inspect brake mechanism.
Clean, repair or replace brake mechanism part (pare 4-30 through 4-35).
19. SERVICE BRAKE RELEASE SYSTEM INOPERATIVE
Step 1. Check for ice or mud in brake mechanism. Pull hub(s) and drum(s) (para 4-60) and visually
inspect brake mechanism.
Expose brakes to warmth. Clean and dry brake mechanism parts.
Step 2. Visually inspect air line between trailer reservoir and manual release valve for dents or
breaks. Cautiously loosen fitting near valve and listen for escaping air. No air escaping
indicates plugged line.
Replace damaged or plugged air line (para 4-39).
Step 3. Check for defective manual release valve (para 4-37g ).
Replace valve (para 4-45).
Step 4. Pull out manual release valve knob. Loosen fitting on line near emergency relay valve. Push
in release valve knob. Air should escape from fitting when manual release valve knob is
pushed in. No air indicates plugged line.
Replace plugged line (para 4-39).
Step 5. Check for defective emergency relay valve (para 4-37f ).
Replace valve (para 4-42).
20. FAIL-SAFE BRAKE MANUAL RELEASE SYSTEM INOPERATIVE
Step 1. Visually inspect air line between fail-safe release tank and manual `release valve for dents
or breaks. Try to pressurize release tank thru the fill fitting from an outside air source;
if this cannot be done, tubing is plugged.
Replace damaged or plugged tubing (pare 4-39).
Step 2. Check for defective fail-safe broke release valve (para 4-37h ).
Replace valve (pare 4-45).
Step 3. Pull out manual release valve knob. Loosen fitting on air line near fail-safe unit. Push
in valve knob. Air should escape from fitting when manual release valve knob is pushed
in. No air indicates plugged line.
Replace plugged line (para 4-39).
21. ONE OR MORE (BUT NOT ALL) FAIL-SAFE UNITS WILL NOT RELEASE
Step 1. Check fail-safe unit for air leak. Air wiil continuously leak from vent hole on fail-safe
cap if defective.
Replace fail-safe unit (para 4-32).
Step 2. Check for ice and mud in brake mechanism. Pull hub(s) and drum(s) (para 4-69) and visually
inspect brake mechanism.
Expose fail-safe to warmth. Clean and dry brake mechanism parts.
22. M746 TRAILER LOW AIR PRESSURE LIGHT COMES ON WHEN BRAKE PEDAL
IS DEPRESSED
Step 1. Visually inspect air line between air reservoir and emergency relay valves for dents or
breaks,
Replace damaged or plugged line (par 4-39).
Step 2. Check for defective low air pressure warning switch (para 4-37j ).
Replace switch (para 4-29).
2 3 . FAIL-SAFE RELEASE TANK DOES NOT PRESSURIZE - MAIN AIR SYSTEM
NORMAL
Check for defective one-way check valve (pare 4-37n ).
Replace valve (para 4-46).
