Emergency Trailer Air Brake

when you pull red button you disable trailer brake air supply and no air in red and blue glad hands. You got US truck!!!! On European semis there are end valves in gald hands and no red button and when driver applies hand brake red glad hand is air supplied but there is full air pressure in service brake glad hand so trailer is locked with service brakes.

Emergency valve on trailer applies park brake if red glad hand is NOT pressurized but on newer trailers only. On old trailers park brakes are applied when trailer air tank is empty. So all depend on trailer design...

 

your trailer has and e brake valve which is probably not releasing. when you pull glad hand that gives it a place to release

 

[I have seen dirt dobbers cause this problem on truck and trailers. When I know one of mine is going to be sitting for a while I use electrical tape on the glad hands. If you have this problem with an out board motors pee tube you can fix it forever by replacing the black hose with a clear plastic tube. For some reason the little dirty thing will not build in a clear hole.

 

My trucks are water trucks that don't always pull a trailer. When I'm not pulling a trailer, I have a set of glad hands with a plug in place of the air line that I use as a dead hand. Put them on the truck glad hands and keeps the lines clear and dry. The trailer glad hands I lock together to keep them clear and dry when not in use.They don't clip all the way but enough to stay together. We don't have "dirt dobbers" but we have leaf cutter bees that will plug up exposed 'holes'.

 

Should be pretty straight forward to check. If you pull the button out and absolutely nothing happens I would say the dash valve is buggered up. There is a vent line, or exhaust line from the dash valve. The yellow and red both exhaust from this. So the vent line would be ok I think. If some air is exhausting there are a couple of other valves in the circuit to the trailer lines. In between the dash valve to the trailer is the tractor protection valve. Trailer air should be just a straight shot through this valve. Most trucks have some sort of in-line quick release valve between the tractor protection valve and the trailer air line. This could be sticking. It might be easier to find the tractor protection valve remove the red line going to it from the dash valve. Push the button in and you should have air. Pull the button out and you should not have air. If air continues to flow, you have a bad dash valve.

 

To be sure I use old galad hand with pressure gauge on it. It is easy to check pressure in service and supply glad hands.

It is the best way for dashboard park brake valve diagnostics.