Once a tractor-trailer loses its air pressure, the air brake system on both the tractor and the trailer can no longer function. As the air pressure decreases, the brake shoes will compress to the inside of the brake drums. Once the air pressure reaches zero, the air brake system will not longer allow the brake shoes to retract or compress. The only method for retracting the brake shoes from the brake drums with no air is to cage the spring brake chamber. Caging the spring inside of the brake chamber will allow the wheels to turn.
Slide under the rear of the tractor-trailer and locate the spring brake chambers that are mounted to the front rear axle. The brake chambers open and close the brake shoes by moving the slack adjusters and the s-cams. Inspect the side of each brake chamber for a T-bolt. The T-bolt has threads on one end with a nut. The other end of the bolt is shaped like a "T." At least one of the brake chambers should come equipped with the T-bolt attached to the side of the brake chamber. If none of the brake chambers has the T-bolt, go to any parts store that sells tractor-trailer parts and purchase a spring brake chamber T-bolt.
Pull the rubber plug out of the front of the spring brake chamber with your fingers. Behind the rubber plug is a threaded hole. Screw the threaded end of the T-bolt clockwise into the hole one complete turn. Turn the nut on the T-bolt clockwise until it compresses against the spring base.
Continue turning the nut on the T-bolt clockwise with the adjustable wrench until the brake shoes unlock. This is called caging the brake shoes. Shine a flashlight through the back of the wheel hub to ensure that the brake shoes have retracted from the brake drum. Keep turning the nut clockwise until the brake shoes are at least a half-inch to 1 inch away from the brake drum. Leave the T-bolt secured to the inside of the brake chamber.
Move to the other spring brake chamber and repeat the same process to retract the brake shoes. Use the flashlight to see the distance of the brake shoes from the brake drum. The trailer can now be moved by towing.
