I had my air brake fail to disingate this morning. I was at a stop light when I turned on the air brake. The idle sounded much louder as it would while the air brake was engaged. When I attempted to accelerate, the more throttle I gave it, the more the truck attempted to declerate. I tried turning off the air brake with no success, and ultimately had to pull into a parking lot and shutoff the truck. I got no check engine light. This has never happened to me until today.