Figure 3.4 shows the braking apparatus for a typical freight car equipped with four-wheel trucks. Notice
that the top rods are connected to the live truck levers by a pin. This connecting point divides the truck-
mounted brake rigging from the body-mounted braking apparatus. When the live truck lever is moved, the
brakes are applied or released depending upon the direction of the lever movement. The braking or releasing
force is transmitted from the live truck lever, the lever that is actuated, to the inside brake beam, through the
bottom rod to the dead truck lever, and then to the outside brake beam. As the two brake beams move, they
apply braking pressure to the four wheels of the truck by forcing brakeshoes against the wheel treads; they
release the braking pressure when moved in the opposite direction.
The truck-mounted brake rigging is connected to the truck side frame by four brake hangers, one at each
end of both brake beams. The dead lever guide provides a connection for the dead truck lever. This guide is
connected to the truck bolster and anchors the dead lever guide at the end opposite the connection with the dead
truck lever.
3.7. SIX-WHEEL TRUCKS
As mentioned earlier, high-speed freight cars and passenger cars are equipped with trucks designed
especially for increased stresses and shocks. The six-wheel trucks give better performance at higher speeds than
four-wheel trucks and absorb more shock and vibration. The safer, smoother riding qualities are necessary for
passenger comfort. The six-wheel truck shown in figure 3.5 has many features common to all passenger car
trucks. Side frames are of much heavier construction than in four-wheel trucks; in addition to coil springs, the
truck is equipped with elliptical springs similar in design to those found on some automobiles and motor trucks.
With a system of equalizers, this combination of springs reduces the sidesway and vertical shocks that would
normally be transferred to the car body. The brake rigging of the six-wheel truck is also different from that of
the conventional four-wheel truck in that two brakeshoes, one on either side of each wheel, make contact with
the wheel tread as contrasted with the four-wheel types that have one shoe per wheel.
Another difference in the six-wheel truck is also shown in figure 3.5. Notice the brake cylinder mounted
on the side of the truck. Some heavy-duty freight cars have depressed centers or well-hole centers, or are
designed in a way that prevents mounting
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