Table 4-3. Organizational Troubleshooting Table - Continued
TEST OR INSPECTION
1. BRAKES WILL NOT RELEASE (cont).
Step 5. Check for closed shutoff valves on towing vehicle.
Open valves if closed.
If valves are open, proceed to step 6.
Step 6. Check for weak or broken brake shoe tension spring.
2. NO BRAKES OR WEAK BRAKES.
Step 1. Check for closed shutoff valves on towing vehicle.
If valves are open, proceed to step 2.
Step 2. Check intervehicular air hoses for proper connection to towing vehicle.
Connect hoses properly.
If hoses are properly connected, proceed to step 3.
Step 3. Check for open drain cock in semitrailer air reservoir.
Close drain cock.
If drain cock closed, proceed to step 4.
Step 4. Check air pressure gage on towing vehicle for low air pressure indication.
Check air lines/connectors for restrictions and/or leakage.
Tighten connections; remove any restrictions from hoses and repair or replace
If air pressure gage indicates normal, proceed to step 5.
If emergency relay valve is not defective, proceed to step 6.
Step 6. Check for air in hydraulic brake system (all models except M127).
If no air in hydraulic brake system, proceed to step 7.
Step 7. Check for leaks in hydraulic system (all models except M127) (para. 4-39d).
Locate leak and tighten or replace broken flexible line or hydraulic line.
If not leaking, proceed to step 8.
Step 8. Check for grease on brake lining.
If brake lining shows no grease, proceed to step 9.