https://www.truck-manuals.net/mack/ 148 OPERATION COUPLING A TRAILER 1. Position the tractor directly in front of the trailer. 2. Back the trailer slowly until the fifth wheel just contacts the trailer plate. 3. Place the transmission in neutral and apply the parking brakes. 4. Connect the trailer glad hands and electrical connector.
CAUTION Make sure the trailer air lines and the trailer electrical cord are properly supported so they will not be pinched or caught while the tractor is being backed under the trailer.
5. Check that the fifth wheel height matches the height of the underside of the trailer. If the trailer is too high, use the landing gear to lower the trailer until fifth wheel and trailer height match. If the vehicle is equipped with an air suspension and the trailer is too low, use the air suspension control switch to exhaust air from the suspension air bags until fifth wheel and trailer height match.
CAUTION Failure to match fifth wheel height with trailer height will result in the trailer being improperly connected.
6. Back under the trailer slowly until the trailer king pin engages. Back slowly to avoid hitting the king pin too hard, and stop as soon as the king pin is locked into the fifth wheel. 7. If equipped with an air suspension, use the air suspension control switch to reinflate the suspension air bags. 8. Raise the trailer landing gear slightly off the ground. 9. With the trailer parking brakes applied, pull the tractor ahead slightly to ensure that the trailer is locked onto the tractor. 10. Push the trailer air supply valve (red octagonal knob) in to supply the trailer system with air pressure. With the air system at normal operating pressure, check the trailer air brake system for excessive leakage and proper operation.
