Fifth Wheel Assembly

A tractor and trailer are separate units joined together by a fifth wheel. The fifth wheel consists of two metal plates: one on the tractor, known as the lower fifth wheel (fig. 7-13, view A), and one on the trailer, known as the upper fifth wheel (fig. 7-13, view B).

The upper and lower fifth wheel form a flexible coupling that permits both rotational and vertical movement between the tractor and trailer. The upper fifth wheel has a kingpin and the lower fifth wheel has locking jaws that lock around the kingpin to couple the tractor-trailer together. The locking jaws is operated by a hand lever that extends to the side of the lower fifth wheel and can be released by either pulling the locking handle forward, as shown in figure 7-13, or pulling the locking handle outward, as shown in figure 7-14.

When the trailer is not connected to the tractor, the front end of the trailer is supported by a retractable two-legged landing gear. The landing gear may be equipped with either wheels or pads (flat pieces of heavy metal). The glad hand connections for the service and emergency air lines and the electrical connection for the clearance, side marker, and brake lights are located on

Figure 7-14.-Fifth wheel locking jaws in open position.

Figure 7-15.-Air and electrical connections.

the front of the trailer (fig. 7-15). Trailers in the NCF normally have two electrical connections adaptable for either a 12- or 24-volt electrical system.