2010 prostar, has a leak from foot valve. Brakes grab when applying light pressure and don't release unless I press real hard on pedal. I have replaced foot valve, front quick release relay, rear quick release relay and still leaking. Losing my mind on what to do next...Any and all help is welcomed!!!
Had a Kenworth with a Wabco anti-lock system that gave me fits sort of like that.
It would leak air and apply brakes . You would have to pull over and pump the brakes to exhaust all your air, and then it would release. The anti-lock would apply or leak, and then would not release air.
Could be as simple as a bad brake can.
I’d start with removing service air line one at a time at each brake can and look for a source of feedback to brake pedal.