I have a problem that I have never heard of before. I'm Bobtailing at the moment, and I have a very odd problem with my truck brakes. At first I thought they were locked up from just sitting, but I have realised sense then that if I push in the truck parking brake and the trailer air supply, and then pull the trailer air supply back out, the brakes release and I can move the truck. I know how to work on simple things, but this is something that I have never heard of before, even the mechanic I called out wasn't sure what could be causing this. Any help is greatly appreciated.