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Chapter 3 Vehicle Construction
mounted to the inner wheel house. The rear body panel
is welded between the quarter panels and forms the rear
portion of the vehicle below the deck lid. The taillights
and the license plates may cover up the rear body panel.
On full-frame vehicles, such as a pickup truck, the
front section is the portion of the vehicle under the hood,
the center section is the cab, and the rear section is the
bed. A full frame, Figure 3-21, provides support for the
vehicle’s body and drive train components. A damaged
full frame can be replaced. The side rails may be boxed
in one area for added strength. Some full frames are
made so that the damaged portion can be replaced as a
section. In some frames, front sections can be replaced.
The frame consists of two side rails joined by cross
members. Some cross members are replaceable. Cross
members may be riveted or welded to the side rails.
Vehicle Production
While it is not within the scope of this textbook to
explain in detail how a vehicle is manufactured, this
section will provide a brief overview of the manufacturing
process. A general understanding of how a vehicle is
made will help you understand how to repair damage.
During vehicle production, sheet metal panels are
stamped by large machines called presses. The presses
form the sheet metal into the desired shapes, such as
single-piece fenders. Complex parts such as doors,
unibodies, and pickup truck cabs are made from several
stamped panels that are welded together. The panels are
fitted into a jig. The jig holds the panels in the proper align-
ment for welding. The parts are spot welded together by
an electric welder. See Figure 3-22. Weld bonding is also
used to join component panels together. In weld bonding,
an adhesive is applied to the panels, the panels are fitted
together, and then they are electric spot welded together.
Some structural parts are joined by a continuous MIG
weld. The MIG weld is usually not longer than 1".
Laser welding joins panels together. This method
allows panels of different thicknesses and strengths to
be joined without any overlap. The laser weld looks like
thin line where the two panels meet. An example of a
laser welded panel is the one-piece door opening panel
on an extended cab pickup truck. The door opening
panel extends from the A pillar to the cab corner and
includes the outer rocker panel and part of the roof. The
door opening panel is made of several differently shaped
pieces laser welded together. The roof piece is thinner
than the A pillar piece. Laser welding allows the manufac-
turer to vary the design strength within one panel.
Welding is not the only way that panels, even struc-
tural panels, can be joined. Aluminum panels together
are sometimes joined by riveting. The rivets are self-
piercing, so no hole is required for insertion. The rivets
eliminate the need for welds.
Full frames can be made by stamping a flat sheet of
steel into a C shape. Two stamped C shapes can be welded
together to form a box. Another way to form a full frame box
is by hydroforming. In hydroforming, a rectangular steel tube
is formed into a complex shape using hydraulic pressure.
Figure 3-20. The rear section of a unibody vehicle
is formed by the rear pillars, rear frame rails, wheel
houses, floor, and rear body panel. (Ford)
Figure 3-21. This steel frame is typical of those used in
late-model pickup trucks. (Ford)
Inner wheel
house house
Rear body Rear body
panel
O O O Ou Ou Ou Ou O t t te r wheel
house
Rear frame
rails
