Truck losing air pressure while stopped can’t find leak

[SquareOne]

Do you think the tractor (or trailer) emergency brake valve is having as issue? Air blowing past the diaphragm when it's under pressure (brakes released).

Last year, I had that issue. Losing air like crazy when going down the highway...literally watching the tank drop and rise, over an over while traveling. When I would pull over, set the brakes, I couldn't find the leak anywhere. Reason being, is that it would only leak when the emergency brake for the tractor was released.

Set your trailer brakes and release the tractor and see if you hear the leak. If that's what it is, it will be leaking substantially.


**edit - just re-read the last line of your first post. Sounds like you tried this already.