21 - 4. FRAME INSPECTION AND REPAIR (Cont' )
Diagonal (skew) Measurement
The following two steps are alternate procedures to determine if
frame rails are skewed.
Measure diagonally from one point on right or left string to adjacent point on opposite
side string. Compare to the opposite diagonal measurement. If these two measure-
ments differ by more than 1/4 in. (6 mm), the two frame rails are skewed. Repeat this
procedure at other sets of four measuring points to confirm skew. Record deviations.
Position a string across two plumb bob points at corresponding (or end) points of frame
rail string. Place a square with one leg coincident with frame rail string. Run a line or
string along other leg of square as far as opposite frame rail string. Measure deviation
of end string and square leg line at opposite frame rail string. Any deviation means the
two frame rails are skewed and, consequently, the crossmembers are not at square
angles to frame rails. A deviation of 1/2 in. (12.7 mm) makes a vehicle "dog track" and
it is difficult to align wheels. Record deviations.
If measured frame rails are out of tolerance, notify supervisor. If
frame rails are verified to be out of tolerance, truck will be
classified as unserviceable.