4 General Information Operating In Bobtail Mode Tractors are equipped with a bobtail air brake proportioning valve which automati- cally redistributes the braking force between front and rear axles when not hooked up to a semitrailer (bobtail operation). When operating in bobtail mode, the rear brake chambers receive reduced or propor- tional brake air pressure. When the tractor is towing a trailer, the rear brake chambers will receive full (normal) brake pressure. NOTE! When operating bobtail, be certain that glad hands, trailer air hoses, electrical cable and connectors are properly stowed and secure. Do not allow them to rub or chafe on other components.
WARNING When operating bobtail, the brake system on the vehicle reduces the possi- bility of rear wheel brake lockup, except on full pedal application. When bobtail- ing, be certain that adequate pedal pressure is applied. There is no need to reduce pedal effort. Failure to do so may result in increased stopping distances.