How can you check if the spring brakes are working when the system air pressure drops below a certain level ?
Park the vehicle on a slight incline, release the atmospheric pressure, set the parking brake, and check for movement.
Park the vehicle on level ground, throttle the wheels, release the parking brake when you have sufficient air pressure, turn off the engine, and hold down the brake pedal and release.
Park the vehicle on level ground, wait for the air pressure to normalize, then release the parking brake, move the truck forward slowly, and apply the brakes firmly with the brake pedal.