four main paragraphs. As you study them, refer to figure 3.2 where the
parts of a typical truck assembly are labeled. Maintenance of safety
appliances is discussed briefly in paragraph 3.13.
3.9. GENERAL TRUCK ASSEMBLY
The general truck assembly should be inspected overall for defective,
cracked, or broken parts. Other than the journal boxes, the only part of
this assembly that needs lubrication is the wearing area of the center
plate. The truck center plate provides a recess for the center pin and a
wearing surface to match the wearing surface of the body center plate. This
connection between the truck and the car underframe allows the truck to
swivel beneath the rigid car underframe to permit the car to negotiate
curves properly. The center plate should always be well lubricated with a
heavy, tacky, or graphited lubricant applied with a paddle. Normally, no
grease fittings are provided for lubricating the center plate.
3.10. BRAKE RIGGING
Although not all of the brake rigging is located on the truck, most of
the mechanical parts are attached to it. Generally the same kinds of brake
parts are used on all trucks, and they should be inspected closely to
prevent the necessity for heavy maintenance and increase the performance of
the equipment. The following subparagraphs discuss preventive maintenance
indicators on the truck brake rigging.
a. Brakeshoe. The part of the brake rigging that actually performs the
braking action is the brakeshoe. When the brakes are applied, the shoe is
pushed against the wheel tread causing a great increase in the friction
resistance to the roll of the wheel. Until recently, brakeshoes were made
of cast iron, and many of them are still in use. However, since they cause
sparking, they are gradually being replaced by composition shoes that last
longer and eliminate the danger of causing fires. The shoe is made of a
softer material than the wheel so that wear occurs on the shoe instead of
the wheel tread. The brakeshoes should be checked to see that they are
tightly attached to the brake hangers and that they seat perfectly against
the wheel treads without binding on or against the wheel flanges. When the
brakes are released, the brakeshoes should separate from the wheel treads at
least 1/8 inch. The shoes should be replaced when their thickness is less
than 1/2 inch.
b. Brake hangers. The alinement of the brake hangers is important
because they hold and position the brakeshoes. The hangers should keep the
brakeshoes in proper alinement with the wheel tread.