15 Oct Air Brake Troubleshooting
Below are some components in an air brake system that can give you trouble within each component is a problem followed by an answer.
Table of Contents
Compressor
Problem – Pumps beyond Cut-out
Answer – Check gauge, check governor-make sure it pressurizes unloader port when above cut-out, check unloader plungers, Lube, kit or change head.
Problem – Won’t Pump Air
Answer – Check gauge, check compressor drive, check inlet valves and plungers – if stuck, should leak at intake when unloaded. Install unloader kit, head kit or head assy.
Problem – Slow Pressure Build-up
Answer – Check gauge, check compressor drive, check for intake restriction, check discharge line for restriction, check unloader function – lube or kit, check inlet and exhaust valves – leak will show at intake when unloaded, kit or change head.
Problem – Pumps Excessive Oil
Answer – Check oil return for restriction or kink, check fro gasket sealant obstructing drain, check for undersize return line – 1/2 min, check intake vacuum 20″ max, check for excessive crankcase pressure, check compressor ring wear – exchange for rebuilt unit.
Safety Valve
Problem – Pops off excessively
Answer – Check system pressure, valve ok if venting 140-150 psi, check governor and unloader.
Problem – Pops off at less than 140psi
Answer – Replace
Problem – Leaks
Answer – Replace
Problem – Won’t function
Answer – Remove and test with shop air above 150psi, replace if non-functional.
Single Check Valve
Problem – Allows bleed back to supply reservoir
Answer – Bleed supply reservoir and watch gauges, check valves should maintain rear and front reservoir pressure, replace if it does not.
Wet Tank
Problem – Excess oil
Answer – (See compressor section pumps excessive oil)
Problem – Excess Water
Answer – Drain Daily, Install Automatic drain, service air dryer.
Problem – Damaged
Answer – replace
Low Pressure Indicator Switch
Problem – Buzzer or Light will not operate
Answer – Check ground and wiring to switch, buzzer and light. Replace switch, buzzer, or light.
Problem – Won’t operate below 60psi
Answer – Check gauge, replace switch, buzzer or light.
Drain Valves
Problem – Manual drain valve leaks
Answer – replace
Problem – Automatic drain valve won’t drain
Answer – repair or replace
Problem – Automatic drain valve won’t drain in cold weather
Answer – replace with heated unit
Problem – Automatic drain valve leaks
Answer – repair or replace
Governor – Air Compressor
Problem – Flutters
Answer – check gauge, check unloader line size is 5/16″ x 5′ max, check for plugged governor reservoir line, repair, adjust, or replace the governor.
Problem – Won’t Pass Air to unloader to cut-out compressor
Answer – Check governor reservoir line, repair or replace.
Primary & Secondary Reservoir
Problem – Excess oil or water
Answer – drain as required, check automatic drain valve on wet tank for proper operation. Check for excessive air leaks that are making the compressor run overtime.
Problem – Excess water
When draining air tanks empty tanks completely, pressure cracking won’t get rid of moisture in the air tanks, because the air pushes the water out of the way, and takes over the drain exit. (Drain Daily)
Problem – Air leaking from tank/tank rusted by mouting bands
Answer – Replace tank
Air Gauge
Problem – Incorrect reading
Answer – calibrate, replace, or see your dealer.
Dual System Foot Brake Valve
Problem – Leaks at exhaust with hand valve applied
Answer – check double check valve, repair or replace check valve.
Problem – Leaks at exhaust with all brakes released
Answer – check anti-compound double check valve for back flow, repair or replace check valve, check foot for inlet valve leak, repair or replace.
Problem – Leaks at exhaust with foot brake applied
Answer – foot valve defective, repair or replace.
Quick-Release Valve
Problem – Leaks (When used on service side)
Answer – Replace, or remove service lines, block wheels and release brakes to see if spring brake is back feeding. You may have to replace a spring brake or the quick-release valve.
Problem – Leaks (When used on spring brake side)
Answer – Replace
Problem – Leaks (When used on a tag or pusher airbag dump system)
Answer – Replace
Service Brake Chamber
Problem – Leaks
Answer – Replace diaphram
Problem – Leaks when it reaches end stroke
Answer – adjust brakes
Problem – sluggish application or release
Answer – check cam operation of basic brake, check air line for restriction or leak, align linkage, check chamber return spring, adjust brakes, check angle – should approach 90 degrees on application, check for dirt and gravel inside chamber- obstruction.
Slack Adjuster
Problem – Sleeve will not depress
Answer – clean and lubricate or replace.
Problem – Adjusting shaft will not turn
Answer – replace
Problem – Cracked housing
Answer – check springbrake anti-compound system, check air chamber size, check to see that adjuster is facing away from chamber.
Problem – Worn Clevis Bushing
Answer – Replace Bushing
Relay Valve
Problem – Leaks at exhaust port with all brakes released
Answer – Remove service line from spring brake to see if air is leaking from service port if so replace the spring brake, check inlet valve in relay valve for leak, check reservoir side of valve for contamination – repair or replace.
Problem – Leaks at exhaust port with service brakes applied
Answer – exhaust valve not seating properly, repair or replace.
Spring Brake Chamber – Parking Brake
SERVICE NOTE: Only service the service side of this chamber do not attempt to remove rear emergency section of the brake chamber. The rear spring is under very high pressure and serious injury or death may occur. Only trained techs should service any part of a spring brake.
Problem – Park brake drags or won’t release
Answer – check for improper adjustment, restriction, or broken line, diaphragm failure, system pressure low, improper manual release, broken return spring, quick release of relay malfunction, broken power spring, replace whole unit or piggy-back emergency section.
Problem – Sluggish Park Application
Answer – Check for failed sprinkbrake diaphragm, improper manual release, broken power spring.
Problem – Leaks when pressurized for park brake release
Answer – check for ruptured spring side diaphragm, push rod seal leakage.
Problem – Service chamber malfunction
Answer – see service brake page in air brake troubleshooting of our truck repair tips.
Double Check Valve
There are three double check valves to check:
1st Type: Double check valve unites front and rear brake reservoirs to feed park control.
Problem – rear tank bleed down, also bleeds from the tank.
Answer – pressure should remain in one tank after the other is drained, replace if inoperative.
2nd Type: Double check valve that separates trailer hand valve pressure from rear foot brake pressure for delivery to a trailer.
Problem – foot valve exhaust port leaks when the hand valve is applied.
Answer – replace
Problem – hand valve exhaust port leaks when the foot valve is applied.
Answer – replace
3rd Type: Double check valve that separates the front and rear axle foot brake pressure and or trailer hand valve pressure for delivery to the trailer.
Problem – Leaks thru foot valve exhaust with hand valve applied.
Answer – replace hand valve or double-check valve that separates trailer hand valve pressure from rear foot brake pressure for delivery to the trailer – test, alternately loosen each inlet line and apply pressure to other, if a leak is detected – replace.
Tractor-Trailer Park Control Valve
Problem – Leaks at exhaust port
Answer – replace
Problem – Park brake won’t release
Answer – check for full system pressure delivery thru valve
Problem – Park brake won’t apply
Answer – replace if it will not release pressure.
Trailer Charge Valve
Problem – Leaks at exhaust port
Answer – replace
Problem – the driver may over-ride automatic trailer brakes when tractor air is below 20psi
Answer – replace if tractor protection is automatic and 2-line, repair or replace stop light switch if tractor protection is automatic and 3-line.
Problem – Won’t apply trailer immediately when pulled
Answer – Replace if it won’t exhaust, repair or replace the stoplight switch or the blue tractor park valve if the trailer charge valve is functional.
Tractor Only Park Valve
Problem – Leaks at exhaust port
Answer – repair or replace.
Two-Line Tractor Protection Valve
Problem – Will not respond to trailer charge valve
Answer – repair or replace
Problem – Supply line to trailer with slow bleed down does not shut off tractor air and vent between 45 and 20psi
Answer – check trailer charge valve, it should pop to let TP valve vent trailer supply, repair or replace.
Problem – Leaks at exhaust port or trailer service port – hand or foot valve or trailer supply.
Answer – repair or replace.
Quick Release & Double Check Valve Combo
Problem – Foot Valve Exhaust leak
Answer – check double check valve portion of feed-back to foot valve, repair or replace.
Problem – Leaks with all brakes released
Answer – repair or replace.
Hand Control Valve
Problem – Leaks at exhaust port when released and foot valve is applied.
Answer – check hand control valve for leak
Problem – Leaks at exhaust port when applied or released.
Answer – repair or replace.
Stop Light Switch
Problem – Leaks
Answer – replace
Problem – fails to signal a good bulb thru sound wiring at 3-6 psi.
Answer – replace
Problem – brake lights stay on when truck is turned off
Answer – replace
Double Dash Valve w/built-in 2-way check
(Red and Yellow Buttons all one unit, usually a MV-2 or MV-3 Valve)
Problem – park brake won’t release
Answer – check for full system pressure delivery thru valve
Problem – park won’t apply
Answer – repair or replace if it will not release pressure
Problem – Leaks at exhaust port
Answer – repair or replace
Problem – Leaks at button, if side pressure is used it leaks less
Answer – replace
Problem – driver may over-ride automatic trailer brakes when tractor air is below 20 psi
Answer – Replace if Tractor Protection valve is automatic and 2-line, repair or replace if TP Valve is automatic and 3-line.
Problem – Won’t apply trailer immediately when pulled
Answer – Replace if it won’t exhaust, repair or replace two-line tractor protection valve if double dash valve is funtional.
Inversion Relay Valve
Inversion Relay Valve with loss of rear service supply, application of springbrake by using the emergency section should be available along with front service brake by applying foot valve.
Periodically test by bleeding rear service tank and observing front brake and rear springbrake application upon depressing foot pedal. Repair or replace if after checking, piping is non-functional.
Problem – Leaks
Answer – repair or replace
Springbrake Control Relay Valve
Problem – Foot valve exhaust leak
Answer – check double check valve portion for feed-back to foot valve, repair or replace.
Problem – Leaks
Answer – repair or replace.
Air Dryer
Problem – Air Leaking constantly from purge valve
Answer – Purge valve seal damaged, replace purge valve seal / purge valve frozen / inspect heater / remove purge tube and push valve shut.
Problem – Heater inoperative
Answer – blown fuse, check fuse and replace with 10 amp / broken wires or poor connections, repair or replace wiring to heater.
Problem – Slow wet tank build-up
Answer – Filter/desiccant cartridge plugged, service dryer. Fitting restriction – ice build up / hose restriction – kinks, collapse, damaged or leaking hose.
