CAUTIONDo not allow water and oil to build up in theair tanks. Excessive amounts of water and oilaffect the operation of the brakes negatively.Each tank has drain valve that should bedrained daily.OPERATIONIn the NCF, tractor-trailer operations are managedby the transportation supervisor. The operation of atractor-trailer is much more difficult than that for mostother vehicles; therefore, operators must be mature,reliable, and experienced.To drive a tractor-trailer safely, you must be able tocontrol its speed and direction. Safe operation of atractor-trailer requires skill in coupling and uncoupling,accelerating, steering, shifting gears, and braking.Additionally, you must remember to make allowancesfor the added length when turning, backing, and passingother vehicles and for maneuvering into position forloading and unloading.Fifth Wheel AssemblyA tractor and trailer are separate units joinedtogether by a fifth wheel. The fifth wheel consists of twometal plates: one on the tractor, known as the lower fifthwheel (fig. 7-13, view A), and one on the trailer, knownas the upper fifth wheel (fig. 7-13, view B).The upper and lower fifth wheel form a flexiblecoupling that permits both rotational and verticalmovement between the tractor and trailer. The upperfifth wheel has a kingpin and the lower fifth wheel haslocking jaws that lock around the kingpin to couple thetractor-trailer together. The locking jaws is operated bya hand lever that extends to the side of the lower fifthwheel and can be released by either pulling the lockinghandle forward, as shown in figure 7-13, or pulling thelocking handle outward, as shown in figure 7-14.When the trailer is not connected to the tractor, thefront end of the trailer is supported by a retractabletwo-legged landing gear. The landing gear may beequipped with either wheels or pads (flat pieces of heavymetal). The glad hand connections for the service andemergency air lines and the electrical connection for theclearance, side marker, and brake lights are located onFigure 7-14.—Fifth wheel locking jaws in open position.7-13
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