182 Section 2 Nonstructural Repairs
Copyright Goodheart-Willcox Co., Inc.
placed on the wheel house and the base of the jack
to spread out the force. At the damage correction
end, a narrow attachment is installed. The narrow
attachment can be used because the quarter panel
overlaps the rear body panel. Because the damaged
area is made of two overlapping panels, it is stronger
and less likely to stretch than a single layer area. If
the metal were a single layer, a broader tip would
be used to prevent stretch. Once the body jack is
in place, the pump is hooked up. Pumping the jack
handle causes the ram is extend and push on the
damage.
A body jack can be used to push out lateral
damage, such as damage to a body line. A piece of
angle iron can be used to concentrate the push on
the body line. When using a body jack, remember
that the base and the attachment must be broad
enough to prevent additional damage.
The duckbill attachment can be used in confined
areas to push out damage. For example, if a door
is hit from the side, the duckbill attachment can be
used inside the door to raise the damage. The duck-
bill consists of a stationary jaw and a movable jaw,
Figure 9-20. The stationary jaw is placed against a
strong base. The movable jaw contacts the damage.
The movable jaw must contact the damaged area
squarely. If only a corner of the jaw contacts the
area to be pushed, stretch damage may result. If
the jaw cannot be positioned to contact the damage
squarely, spread out the force with a block of wood.
There will not be much travel in the movable jaw.
It may be necessary to place wood blocks between
the jaw and the damage to provide sufficient reach.
Stretching
When metal is upset, its surface area is reduced
and its thickness is increased. Stretching restores the
metal to its correct dimensions. To stretch metal, place
a dolly on the inside surface of the damaged panel
and use a stretching hammer on the outside surface.
Hammering on the dolly causes the upset metal
between the dolly and the hammer to thin out. This
thinning is a rearrangement of the metal grains. As the
metal gets thinner, its surface area is increased. The
increase in surface area restores the proper dimen-
sions to the upset metal. The dolly used for stretching
must match the shape of the undamaged panel. Hold
the dolly tightly against the upset metal. Hammer
rapidly, with at least one blow per second. With each
blow, the dolly should ring like a bell. Push the dolly
out to meet each blow. When restoring the crown to an
upset panel, stretch the panel starting from the ends
and working toward the center. See Figure 9-21. If the
center of the damage is raised first, the crown will not
be restored.
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
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Figure 9-20. The stationary jaw is located at the
bottom on this duckbill attachment. The movable jaw
is at the top.
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Figure 9-19. This hydraulic ram rests on a block of
wood positioned between the ram and the wheel
house.
Wood block Hydraulic ram