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Chapter 8 Nonstructural Panel Repair
Tight double folds caused by longitudinal force will
also need stretching. With the damaged panel under
tension, the folds can be stretched to restore length. Do
not hammer on the folds until the tension force begins
to unlock them. Hammering before tension unlocks the
folds will create additional damage, making the folds
even stronger.
An upset can cause false stretch, or “oil can,” in an
adjacent area. A false stretch is a bulge that pops in
when pressed and out when released. To demonstrate
false stretch, take a piece of paper and make a tear
perpendicular to one edge. Overlap the edges of the
tear. The overlap represents the upset, or decrease in
surface area. The overlap causes a bulge in the paper
adjacent to the overlap. On a vehicle, a decrease in
surface area causes a bulge, or false stretch, in the
adjacent low-crown area.
False stretch may be present before repairs begin
or may appear during straightening. If false stretch is
present, look for an upset in nearby metal. Removal of
the upset by stretching will relieve the false stretch. The
upset is often in an adjacent body line. If the back side
of the panel is accessible, place a body chisel on the
back of the body line and tap along the chisel’s face
from the outside of the panel. This will stretch the body
line, relieving the false stretch.
If false stretch is present but an upset cannot be
found, or if only the outside of the panel can be worked,
locate the nearest body line. Use a dinging hammer to
tap on the body line. This may relieve an upset that is
present in the body line, causing the false stretch to firm
up. If an upset cannot be located and tapping on the
nearest body line does not work, the false stretch can
be eliminated by shrinking. Shrinking techniques will be
covered in detail later in this chapter.
Leveling
When high areas and low areas are found next to each
other, leveling is used to raise the low areas and lower g
the high areas. If the damage did not cause a change in
surface area, leveling will restore the panel contour.
During leveling, a dolly with the same contour as the
undamaged panel is used under the low areas, while a
flat-faced dinging hammer is used on the high areas. The
dolly pushes up on the low areas as the hammer taps on
the high areas. Think of the dolly as providing the direc-
tion of the movement and the hammer taps as providing
the vibration for the movement. See Figure 8-22. The
hammer does not beat the high area down. Instead, it
vibrates the high area. This hammer-off-dolly technique
causes the dolly to rebound and raise the low area. The
tapping gradually lowers the high area.
A hammer-on-dolly technique with a dinging hammer
may also be used to raise low spots. Light taps, not bell-
ringing taps, will raise the metal without stretching. Light
hammer-on-dolly blows can be used to level a folded
flange. Reverse-crown areas can be leveled with a high-
crown hammer, as shown in Figure 8-23. The high-
crown hammer will fit into the reverse crown in order to
lower a ridge.
Leveling can also be done on a low-crown panel
during tension repairs. The damaged panel shown in
Figure 8-24 has minor folds caused by longitudinal
force. The metal is pushed in at B and pushed out at B
A. As corrective force is used to lengthen the panel, the
dolly is used to hold the metal out at B. As the metal
moves at B, A will move also. Tapping with a hammer
at A vibrates the metal and helps it move in to its proper
contour. Leveling a low-crown panel requires less force
than leveling a high-crown panel.
Raising
Low areas can be brought up with a raising opera- g
tion. There are several techniques used to raise damage.
Panel
Dolly
Body
hammer
Figure 8-22. This diagram shows the leveling process
for a high-crown panel. (Toyota)
Figure 8-23. A high-crown hammer can be used to
level a reverse-crown area.