Table 4-2. Unit Troubleshooting (cont'd)
TEST OR INSPECTION
Step 5. Check relay valve and brake chamber.
Apply towing vehicle brakes and release. Relay valve should vent
brake chamber air through exhaust port when brakes are released.
If air is not vented from brake chamber, replace relay valve.
If relay valve is not defective, but brake chamber is defective, replace
If relay valve and brake chamber are not defective, proceed to step 6.
Step 6. Check for weak or broken brake shoe return spring (1).
If return spring is defective, replace spring.
If return spring is not defective, proceed to step 7.
Step 7. Check for out-of-adjustment brakes.
Adjust brakes if out-of-adjustment (para. 4-50 (XM1063)
or 4-51 (M129A4)).
11. NO BRAKES OR WEAK BRAKES
Step 1. Check to see if shutoff valves on towing vehicle are open.
If valves are closed, open shutoff valves.
If valves are open, proceed to step 2.
Step 2. Check intervehicular hoses for proper connection.
If hoses are not properly connected, connect hoses properly.
If hoses are properly connected, proceed to step 3.
Step 3. Check to see if any drain cock is open.
If any drain cock is open, close drain cock.
If all drain cocks are closed, proceed to step 4.
Step 4. Check for low air pressure.
Check air pressure gage on towing vehicle.
If air lines are restricted, remove restrictions.