An overload warning system for a trailer brake cylinder of a trailer brake system having a nominal deceleration rate. It has been found that previous temperature sensing overdue warning systems have a disadvantage that undue delay occurs and that no warning signal is initiated until after damage to the trailer brakes occurs. The present invention proposes that the tractor brake system and the trailer brake system compare their received operating control signals from which they form a ratio factor and then produce a warning signal when the ratio factor changes beyond a predetermined critical change velocity. The present invention employs the rapid drop in braking force caused by a brake overload and uses the rapid drop and increase brake demand for readjusting the brake deceleration. The present invention is used for uniquely recognizing the "Fading" effect of the trailer brake system.