Trailer brakes, air leaks back thru apply

I don't know if it is a fault but I ran into the same issue when towing a tilt equipment trailer behind a dump.
I could not keep the trailer brakes from locking under normal braking when empty, so I cut a piece of soda can to block the service line to the trailer (between the glad hands).

The trailer brakes would apply after a short time due to air leaking over from the supply to the service side.
I had to disconnect service side and plug truck gladhand to disable trailer brakes.

I don't know if this is a feature or a defect, as I only tried it on that one trailer to get the stupid thing moved without destroying the tires.

 

Pull glad hand off and c/k for air coming from trailer glad hands sounds like a relay valve

 

I see a lot of relays go bad a few months old quality is definitely going down did you check emergency and so the brakes take a while to set like its dumping all the air out of the tanks

 

could it be the tractor protection valve gone bad?

 

Need to remove the blue glad hand from the trailer when this happens and see if the air is leaking from the truck or the trailer blue line glad hand. If leak is from truck I would say tractor protection valve.

 

is it only on one trailer or every trailer u hook to? maybe for some odd reason the lines on the trailer are backwards.

 

If its blowing back though the service on the trailer as the video shows it is likely either the service brake relay valve on the trailer or the spring brake valve on the trailer.