185 Chapter 9 Nonstructural Panel Repair Copyright Goodheart-Willcox Co., Inc. 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 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 pick. Pry pricks are often used in confined areas or areas with limited-access, such as the inside of a door or fender. The pry pick is inserted from behind the Toyota Figure 9-22. This diagram shows the leveling process for a high-crown panel. Panel Dolly Body hammer Goodheart-Willcox Publisher Figure 9-23. A high-crown hammer can be used to level a reverse-crown area.