Help Trailer not using emergency air, won't pass test

My tractor and trailer is giving me grey hairs fast. I am trying to go for my class A on Thursday and I am having problems with my trailer. Here is what it is doing. When I do my test in cab to lower the air pressure the trailer brakes never pop out. The air pressure on primary and secondary drops to zero and still does not pop. If I pull the emergency glad hand it has full pressure in it and when released it will pop the in cab valve. Yesterday the trailer passed the test with no problems. Any help would be greatly appreciated. When it rains it pours.

Thank you
Ryan

Ok, so you are saying that if you drain the tanks to 0, and then pull the emergancy gladhand, it still has full pressure on it and once that drains then the trailer brake pops out in the cab?

The valve is supposed to pop between 45-20 psi. I pump the brakes to 0psi and the valve does not pop (yesterday it did). I then go pull the emergency glad hand which should have no pressure and it releases a large surge of air and the valve then pops out. For some reason the trailer is not drawing off of all air tanks.

Thanks
Ryan

Ok, if when everything is pumped up, and the trailer is charged, do the brakes on the trailer set immediatly when the trailer valve is pulled out?

If they do, you have a bad trailer valve. If they don't you have a bad tractor protection valve.

What truck is this on? dirt is the leading cause of failure in these valves.

Ferroequinologist said:

Ok, if when everything is pumped up, and the trailer is charged, do the brakes on the trailer set immediatly when the trailer valve is pulled out?

If they do, you have a bad trailer valve. If they don't you have a bad tractor protection valve.

What truck is this on? dirt is the leading cause of failure in these valves.

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Okay with a full charge when I pull the valve it takes about 2-3 seconds for the brakes to apply. It is now starting to work better. I put some oil in the glad hands and actuated the trolley valve many times. If I pump the brakes hard and wait a few seconds in between pumps the valve is popping consistently at 30PSI as it should. This trailer is behind my M931.

Thanks
Ryan

You will not be able to take a class a test in your truck. It's systems are too different than a std our truck and the person giving you the test does not have the correct criteria on it to test you. You will also be limited to auto trans only.


you have an emergency tank on your mil truck that civi trucks don't have and it's not going to test right. How it all works I'm not 100% sure of but it's not going to test the same as an Otr truck.

jwaller said:

You will not be able to take a class a test in your truck. It's systems are too different than a std our truck and the person giving you the test does not have the correct criteria on it to test you. You will also be limited to auto trans only.

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Several people have taken the test in 900 series trucks here and passed. And yes I will have a restriction for auto only till I take the F750 Manual trans down retake the test and have that restriction removed

Glad you got it working

Sounds like your red valve(trl supply and emergency) is sticky. When you pump the brakes like that, with the engine off, your emergency valve should pop around 40-45 psi, and you yellow valve(tractor parking) should pop at 20 psi.

If you pull on the yellow, and not hold the red in, the red must pop when you pull the yellow.

And Waller is right- the third valve is a get out of here right now- it takes the springs off the brakes so that you can move. However, you won't have service brakes until the air comes up.