How do you inspect air brakes on a truck?

Answer 1

With a flashlight and either a 32nds gauge or a tape measure. Ensure your brake shoes have, at an absolute minimum, 4/32nds of depth on them. Check exposed areas of the brake drum interior to ensure that there are no signs of cracking. Once that's done, hop in the cab, turn the key to the on position (but don't start the vehicle), put the vehicle in gear, then release the brakes. Once the pressure drop from releasing the brakes has stopped, depress the brake pedal and hold it for one minute. You should not lose more than three psi in one minute for a single vehicle or more than four psi in a minute for a combination vehicle (with an air brake equipped trailer). Once that's done, you'll test the tractor protection valve and brake control valve. If you have a red trailer air supply valve and have the emergency air to the trailer disconnected, you can push and hold that in. At some point, when the air pressure is between 60 and 20 psi, the brake control valve should pop out.