Hello everyone. I have a 1990 f-800 w/air brakes. I have a leak coming from the quick release valve on the rear brakes. I don't know what is causing it. I pulled the release valve off and everything checks fine.I don't know if the tredle pedal valve is causing it or what. If someone could chime in and give me some things to check and how to check I would very much appreciate it.

 

I think we need a little more info on this. Quick release valves do not
leak unless you apply the brakes. And usually they have two quick
release valves one for service brakes and one for emergency chambers.
Id replace it they are a dime a dozen most likely a hairline crack in its
plastic (junk) I like the old ones made out of alum.

Myself I would disconnect the line in from treadle to quick release and see if
its weeping air if so the treadle is not closing. quick release valves needs a
good shot of air to overcome the spring and rubber seat and if the treadle
weeps it probably will weep out of the exhaust port on the Q release valve.
All I can think of cause your truck isnt here.

 

Sorry Big Job. You are correct. It is continuously coming out of the service brake one. Not the emergency. Though you are right about the plastic ones being junk , mine is the aluminum type. I was leaning towards the tredle valve as well.

 

Well it turns out I have a bad brake diaphragm/ chamber. I pulled the air line off the chamber to see if in fact air was leaking past it and low and behold I found which one it was.

 

Always remember one thing with brake application valves, the exhaust port is almost always open, with almost no exceptions. Sooo, that being said, if a valve is leaking out the exhaust without the circuit being used, it (the leaking air) is coming form another source.

If a service quick release is leaking with the service brakes released, and the spring brakes released (air applied), the one point these 2 circuits come close together is within the brake chamber, at the pushrod seal between the service and emergency diaphragms. The leak should go away when the spring brakes are applied (air released). The only other place would be the two-way check (if used) being defective at the emergency relay that acts as an anti-compounding feature. What this (anti compounding) does is prevents overloading the foundation brake mechanical capacity by using service application air to release the spring brake if the emergency circuit is exhausted (parked). It prevents both circuits from applying the mechanical components. The two way check keeps the service and emergency systems from backfeeding air through each other, resulting in a major leak. After thinking about it, even this should not allow a leak @ the quick release, since the anti compounding 2 way check is in line in the control side of the service system relay valve, and the quick release is down stream of the relay valve-- but you would have an air leak at the treadle valve and/or hand spike, at which point there is another 2 way check if it is a tractor, because the anti compounding would be between the control of the service side, and the control of the emergency side. Without a diagram, it is difficult to conceptualize.

I ain't perfect but do have a lot of experience with air brakes, (30 years) and an ASE master truck tech cert, with a NY HABS cert (HABS- heavy advanced brake systems). I've made a lot of mistakes many of you folks have, and hopefully I can prevent somebody from making the same ones. If I can be of assistance, I will help all I can.