METAL BODY REPAIR - OD1653 - LESSON 1/TASK I
rectangles may be laid within them which provide good diagonal tests.
(14) The measuring device, called a tram (figure 17), is a telescoping
tube equipped with an extension clamp which fixes it as the measurement of
one diagonal for comparison with another.
FIGURE 17. TRAM.
(15) Since most severe collisions distort the frame as well as the body
of the motor vehicle, the frame must be checked and straightened first.
Divide it into three rectangles, using as corners the front and rear spring
shackles as in figure 18 (on the following page).
Then lay the tram at diagonal AB'; clamping it at the exact length of the
diagonal. Remove the tram and check A'B to see whether this length is the
same. In the same way check BC' against B'C and CD' against C'D. If there
is any deviation of measurements, do not check body alignment until
corrective forces have been applied to bring the frame into line.