AIR BRAKE SYSTEM TROUBLESHOOTING

1 AIR BRAKE SYSTEM TROUBLESHOOTING . Page 10 QUALITY HEAVY DUTY PARTS. 10 5/27/2004, 7:59 PM. AIR BRAKE SYSTEM TROUBLESHOOTING . QUALITY HEAVY DUTY PARTS Page 11. 11 5/27/2004, 7:59 PM. AIR BRAKE SYSTEM TROUBLESHOOTING . 1.) Before replacing any valve with a new or remanufactured valve, be sure to blow the air lines out either using the vehicle's own air supply or shop air. Dirt is the greatest cause of premature air valve failure. 2.) If pipe dope is used on fittings, use it sparingly. This can also get into the unit and cause a failure. 3.) When installing fittings into a remanufactured valve, do not over tighten or it will crack the casting. 4.) With the introduction of spring brakes, anti-compounding and 121 air BRAKE systems, because a valve is leaking air out of its exhaust, does not mean the valve is at fault. If a spring BRAKE is leaking from the the spring BRAKE to the service BRAKE side, that air will travel back up the service line and out the exhaust of the next valve back.

2 Before replacing a valve that has air leaking from its exhaust, disconnect the delivery lines from that valve to determine if air is being fed back from some other valve or unit. TRUCKS, TRACTORS and BUSES. 1.) Insufficient Brakes 7.) Uneven Brakes 11.) Air Pressure Drops Quickly With -Brakes need adjusting, lubricating or relining. -Brakes need adjusting, lubricating or relining. Engine Stopped and Brakes Released -Low air pressure in the BRAKE SYSTEM (below 60 -Improper axle mounting. -Leaking BRAKE valve. psi). -Grease on BRAKE lining - reline brakes. -Leaking tubing or hoses. - BRAKE valve delivery pressure below normal. - BRAKE shoe return spring broken. -Compressor discharge valves leaking. -Wrong size actuators and/or slack adjusters. - BRAKE drum out of round. -Governor leaking. -Failure of part of a dual air SYSTEM . - BRAKE chamber diaphragm failure. -Excessive leakage elsewhere in the air BRAKE supply -If remote mounted BRAKE valve, check linkage.

3 -Wrong BRAKE lining. SYSTEM . -Broken slack adjuster or foundation BRAKE parts. -Inadequate reservoir volume - high air demand. 2.) Brakes Apply Too Slowly -Brakes need adjusting or lubricating. -Low air pressure in the BRAKE SYSTEM (below 60 8.) Air Pressure Will Not Rise To Normal 12.) Air Pressure Drops Quickly With psi). -Faulty air gauge (registering incorrectly). Engine Stopped and Brakes Fully Applied -Insufficient BRAKE valve delivery pressure. -Excessive valve or fitting leakage. -Leaking BRAKE chamber, actuator, rotochamber or -Excessive leakage with brakes applied. -Governor out of adjustment. BRAKE cylinder. -Restricted tubing or hose. -Slipping compressor drive belt. -Valve left open. -Treadle travel restricted. -Faulty compressor. -Leaking BRAKE valve. -If remote mounted BRAKE valve, check linkage. -Broken supply line. -Leaking tubing or hose line. -Excessive water in reservoirs. 3.) Brakes Release Too Slowly -Inadequate reservoir volume.

4 -Brakes need adjusting or lubricating. 9.) Air Pressure Rise To Normal - BRAKE valve not returning to fully released Too Slowly position. -Excessive valve or fitting leakage. 13.) Compressor Knocks Continously -Restricted tubing or hose. -Excessive reservoir volume. -Exhaust port of BRAKE valve, quick release valve, or or Intermittently -Clogged compressor air strainer. relay valve restricted or plugged. -Loose drive pulley. -Engine speed too slow. -Faulty BRAKE valve, quick release valve, or relay -Back lash in drive gears or drive coupling. -Compressor discharge valve or inlet valves valve. -Worn or burnt out bearings. leaking. -If remote mounted BRAKE valve, check linkage. -Excessive carbon deposits in compressor cylinder -Compressor drive belt slipping or faulty drive head. coupling. 4.) Brakes Do Not Apply -Worn compressor. -No air pressure in BRAKE SYSTEM . -Excessive carbon in compressor cylinder head or -Restricted or broken tubing or hose.

5 14.) Safety Valve Blows Off . discharge line. -Faulty BRAKE valve. -Safety valve out of adjustment. -Air pressure in the air BRAKE SYSTEM above normal If remote mounted BRAKE valve, check linkage. 10.) Air Pressure Rises Above Normal due to faulty unloader mechanism or faulty governor. 5.) Brakes Do Not Release -Faulty air gauge ( registering incorrectly). - BRAKE rigging binding. -Governor out of adjustment. - BRAKE not in fully released position. -Faulty governor and safety valve. 15.) Excessive Oil or Water in the -Faulty BRAKE valve or relay valve. -Restriction in line between governor and BRAKE SYSTEM -Restricted or collapsed tubing or hose. compressor or restricted unloading valve. -Reservoirs not being drained oftern enough. -If remote mounted BRAKE valve, check linkage. -Too much clearance at compressor unloader -Compressor passing excessive oil. valves or compressor unloading mechanism stuck -Compressor air strainer restricted.

6 6.) Brakes Grab or Erratic BRAKE in closed position. -Excessive engine oil pressure. -Grease on BRAKE lining = reline brakes. -Back pressure from engine crankcase. -Faulty BRAKE valve or relay valve. -Excessive oil (flooding) in compressor crankcase. - BRAKE rigging binding. -No vehicle load = high BRAKE pressure. Page 12 QUALITY HEAVY DUTY PARTS. 12 5/27/2004, 8:02 PM. AIR BRAKE SYSTEM TROUBLESHOOTING . 1.) Before replacing any valve with a new or remanufactured valve, be sure to blow the air lines out either using the vehicle's own air supply or shop air. Dirt is the greatest cause of premature air valve failure. 2.) If pipe dope is used on fittings, use it sparingly. This can also get into the unit and cause a failure. 3.) When installing fittings into a remanufactured valve, do not over tighten or it will crack the casting. 4.) With the introduction of spring brakes, anti-compounding and 121 air BRAKE systems, because a valve is leaking air out of its exhaust, does not mean the valve is at fault.

7 If a spring BRAKE is leaking from the the spring BRAKE to the service BRAKE side, that air will travel back up the service line and out the exhaust of the next valve back. Before replacing a valve that has air leaking from its exhaust, disconnect the delivery lines from that valve to determine if air is being fed back from some other valve or unit. TRAILERS. ** The air BRAKE SYSTEM of a trailer is 3.) Brakes Release Too Slowly 7.) Uneven Brakes entirely dependent upon the air BRAKE -Brakes need adjusting or lubricating. -Brakes need adjusting, lubricating or relining. SYSTEM of the towing vehicle for its air - BRAKE rigging binding. -Grease on BRAKE lining - reline brakes. -Exhaust port of relay emergency valve restricted or - BRAKE shoe return spring broken. supply and control. Therefore, the air air plugged. - BRAKE drum out of round. BRAKE SYSTEM of the towing vehicle must -Restricted tubing or hose. -Leaking BRAKE chamber or actuator diaphragm.

8 Be in good condition; otherwise it will be -Restricted tubing or hose. impossible to obtain a good BRAKE 4.) Brakes Do Not Apply -Broken slack adjuster or foundation BRAKE parts. -Connecting hoses to trailer crossed. performance on the trailer. Before -Faulty relay emergency valve. condemning the air BRAKE SYSTEM on a -Tractor protection valve not functioning properly 8.) Excessive Leakage With Brakes Released trailer, always be sure the air BRAKE or not in normal position (see operating instruc- -Relay emergency valve or drain valve leaking. SYSTEM on the towing vehicle is function- tions). -Leaking tubing or hose. -No air pressure in air BRAKE SYSTEM . -Hose uncoupled or leaking hose coupling. ing properly. The following is based on -Restricted tubing or hose. on the assumption the tractor air BRAKE -Hoses between tractor and trailer not connected. SYSTEM is functioning properly. 9.) Excessive Leakage With Brakes 5.

9 Brakes Do Not Release Fully Applied -Connecting hoses to trailer crossed. -Faulty relay emergency valve. 1.) Insufficient Brakes - BRAKE valve on towing vehicle in applied position. -Brakes need adjusting, lubricating or relining. -Leaking BRAKE chamber diaphragm. - BRAKE rigging binding. -Leaking tubing or hose. -Tractor protection valve not in normal position. -Relay emergency valve in emergency position. -Faulty relay emergency valve. -Hose uncoupled or leaking hose coupling. -Faulty relay emergency valve. -No trailer air supply - clogged emergency line. -Restricted tubing or hose. -Low air pressure in the BRAKE SYSTEM (below 80 -Tractor protection valve not functioning properly psi). 10.) Excessive Leakage with Relay or not placed in normal position. Emergency Valve in Emergency Position - BRAKE valve delivery pressure in towing vehicle below normal. -Faulty relay emergency valve. 6.) Brakes Grab -Restricted tubing or hose.

10 -Grease on BRAKE lining - reline brakes. -Wrong size actuators. - BRAKE rigging binding. 11.) Excessive Oil and Water Present -Faulty relay emergency valve. in the Air BRAKE SYSTEM . 2.) Brakes Apply Too Slowly -Faulty BRAKE valve on towing vehicle. -Reservoirs not drained often enough. -Brakes need adjusting or lubricating. -No trailer load. -Low air pressure in the BRAKE SYSTEM (below 80. psi). - BRAKE valve delivery pressure in towing vehicle below normal. -Restricted tubing , hose, or line filter. -Excessive leakage with brakes applied. -Faulty relay emergency valve. QUALITY HEAVY DUTY PARTS Page 13. 13 5/27/2004, 8:02 PM. AIR BRAKE SYSTEM TROUBLESHOOTING . PROBLEM CAUSE REMEDY. 1) Dryer is constantly cycling a. Excessive SYSTEM leak. a. Repair air leak. or purging. b. Defective governor. b. Check governor for proper cut-in, cut-out . c. Defective one way valve between pressure and excessive leakage. Repair or air dryer and wet tank.