Figure 38-2. Truck Tractor and Semitrailer connections.
is a permanently attached kingpin by which the truck
blocks bolted to a bedplate, which is mounted on the
tractor pulls the semitrailer (fig. 38-3).
frame of the truck tractor.
There are three types of fifth-wheel couplings:
38-3. Fifth Wheel. The lower fifth wheel (fig. 38-4)
permanent, semiautomatic, and automatic.
contains the movable parts of the fifth-wheel assembly
permanent fifth-wheel coupling, the kingpin is made part
and supports the semitrailer load thrust on the truck
of the lower fifth-wheel plate, and, once it is locked In
tractor. The circular portion of the heavy cast steel plate
position, the truck tractor is operated with the same
is the bearing surface upon which the upper plate of the
semitrailer at all times. In semiautomatic and automatic
semitrailer rides. The circular groove In the lower plate
fifth-wheel couplings, the kingpin is contained on the
is a grease retainer for lubricating the rubbing surfaces of
upper fifth- wheel plate. The kingpin is locked In position
the upper and lower plates. The sloping ramps aid In
by a kingpin lock, which is a ring on the lower fifth wheel
picking up the upper plate of the semitrailer. The wide-
that clamps around the kingpin. In the semiautomatic
open space between the ramps guides the kingpin Into
coupling, which is the most popular type, the kingpin lock
place. The lower plate is pivoted on a rocker pin
(fig. 38-4) is operated by a hand lever that extends to
crosswise to the truck tractor, providing a free swinging
the side of the lower fifth wheel. The automatic coupling
movement between the semitrailer and truck tractor. The
is locked In a
outer ends of the rocker pin are supported in pillow
Figure 38-3. Kingpin and Plate.