Do not allow water and oil to build up in the
air tanks. Excessive amounts of water and oil
affect the operation of the brakes negatively.
Each tank has drain valve that should be
In the NCF, tractor-trailer operations are managed
by the transportation supervisor. The operation of a
tractor-trailer is much more difficult than that for most
other vehicles; therefore, operators must be mature,
reliable, and experienced.
To drive a tractor-trailer safely, you must be able to
control its speed and direction. Safe operation of a
tractor-trailer requires skill in coupling and uncoupling,
accelerating, steering, shifting gears, and braking.
Additionally, you must remember to make allowances
for the added length when turning, backing, and passing
other vehicles and for maneuvering into position for
loading and unloading.
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.