183 Chapter 9 Nonstructural Panel Repair
Copyright Goodheart-Willcox Co., Inc.
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 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 direction of the movement and the
hammer taps as providing the vibration for the move-
ment. See Figure 9-22. 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 9-23. 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 9-24 has minor folds caused by longitudinal
force. The metal is pushed in at B and pushed out at 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
operation. There are several techniques used to raise
damage. One way to raise a low spot is to use a pry
Goodheart-Willcox Publisher
Figure 9-23. A high-crown hammer can be used to
level a reverse-crown area.
Goodheart-Willcox Publisher
Figure 9-21. This diagram shows how to stretch
metal to restore crown. Using the hammer-on-dolly
technique, start at the edges and work toward the
center.
Toyota
Figure 9-22. This diagram shows the leveling process
for a high-crown panel.
Normal contour
Damaged panel
Dolly
Panel
Dolly
Body
hammer