Trailer air supply valve.

[MurphyT]

The trailer air supply valve will not stay engaged by itself. The trailer does charge if I hold it in but then the yellow valve pops out as well. Weird. No major leaks. Lots of air pressure. Tried several trailers. Same story. Ideas?

 

[Spyder]

Sure sounds like an air leak to me. Watch the air pressure gauges. Are they dropping? The yellow(truck brake supply valve) is supposed to pop when air pressure drops below a set psi.

 

[MurphyT]

Steady pressure.

 

[Hammer166]

Probably the dash valve assembly is bad. @r3gulator3 is the go to guy on this stuff.

 

[r3gulator3]

My best hip shot would be a bad dash valve.

 

[Spyder]

Steady pressure.

In that case start with the dash valve. Chock the wheels and bypass it with the engine off, air empty. Fire the engine up and see if it builds pressure normally. If so put a new dash valve in it.

 

[MurphyT]

I've already done that. Brand new valve. Same results.

 

[r3gulator3]

Then, you’ve got something leaking somewhere. Either a brake can leaking back on the service side, through a relay valve, or the inturnals of the tractor protection valve is back feeding. Or, someone hooked some shit up wrong on your valve to mess with you.