54 Section 1 Introduction to Collision Repair
Introduction
This chapter explains the various vehicle classifi ca-
tions, describes the materials used to construct a vehi-
cle’s body, and identifi es typical body components. It also
provides a brief overview of the automobile manufacturing
process. An understanding of the material presented in this
chapter will help prepare you for the chapters that follow.
Vehicle Classifi cations
There are several ways to classify vehicles. In addi-
tion to the obvious classifi cations of year, make, and
model, vehicles are often classifi ed by construction type,
body type, and drive train confi guration. The following
sections detail the most common vehicle classifi cations.
Vehicle Construction
One common way to classify vehicles is by the way
they are constructed. Vehicles are commonly classi-
fi ed as either full-frame vehicles or unibody vehicles.
A full-frame vehicle has a body and a separate
frame. See Figure 3-1. The frame is made from steel
or aluminum that ranges in thickness from 1/8"–1/4".
The main body structure is made from 18–22 gauge
sheet metal panels that are spot welded together. The
body is mounted on rubber isolators and bolted to the
frame. External panels are bolted in place on the main
body structure and the frame. External panels include
bumpers, fenders, doors, hoods and deck lids. These
panels are made from steel, aluminum, or plastic.
A damaged welded panel on a full-frame vehicle
can be replaced by drilling out the spot welds, removing
the damaged panel, and welding a new panel in place.
Damaged bolted panels can be replaced by unbolting
and removing the damaged panel and bolting on a new
panel. Full-frame vehicles include pickup trucks, as well
as some sport utility vehicles, vans, and full-size cars.
One drawback to vehicles with a full steel frame is that
the frame is heavy. This weight reduces fuel economy.
Aluminum frames weigh less than steel frames.
Unibody construction is used on most passenger
cars. A unibody vehicle is constructed of sheet metal
panels that are spot welded together to form the main
body structure. See Figure 3-2. These panels provide
the structural support for the vehicle, eliminating the
need for a separate frame. Therefore, a unibody vehicle
weighs less than a comparable full-frame vehicle,
making it more fuel effi cient. Unibody vehicles also
have bolted-on external panels, such as fenders, hood,
deck lid, doors and bumpers. Damaged panels on a
unibody vehicle can be replaced in the same way they
are replaced on the body portion of a full-frame vehicle.
Most unibody vehicles are made of steel, but a few are
made of aluminum.
Body
Frame
Figure 3-1. This phantom view shows the body and frame
of a full-frame sport-utility vehicle. The body is bolted to the
frame. Isolators between the frame and body help minimize
vibration transferred to the passenger compartment. (Ford)
Figure 3-2. The unibody consists of sheet metal
panels that are welded together. (Ford)