Proper body alignment is critical in order to ensure normal
life and function of many parts on the vehicle. Check the body alignment if
the vehicle has been involved in a fire, collision, or has
been overloaded. If you suspect poor alignment for any other
reason, check the body alignment. Refer to
Alignment Checking
.
Certain conditions may make the body appear to be out of alignment when,
in fact, the body is aligned. For specific conditions, refer to
Alignment Checking
.
Terms used in this section are briefly defined as follows:
| • | Section Modulus is a measure of the strength of a frame based
on height, width, thickness, and shape of the side rails. Section Modulus
does not account for the strength of the material used. |
| • | Collapse refers to the
condition that occurs when buckles appear on one or more than
one surface of the box section of the side rails (1and 2), or when a section
of the underbody or the structure has been shortened in length. |
| • | Diamond refers to the
condition where one side of the underbody structure has been moved forward
or rearward causing the underbody structure to be out of square. |
| • | Sag refers to a vertical
misalignment resulting in an incorrect datum line. When both sides are equally
misaligned, this condition is known as kick-up. |
| • | Sidesway refers to a section
of the frame that is positioned to the left or the right of centerline, when
compared to the rest of the vehicle. |
| • | Tracking refers to the alignment of the vehicle axles with each
other. A misaligned frame can cause improper tracking. If the vehicle is tracking
correctly, all axles will be parallel to each other and perpendicular
to the centerline of the body. |
| • | Twist refers to the condition
where the sides of the underbody plane (the datum) are not parallel. One
rail will slope up while the other rail will slope down. |
| • | Datum refers to an imaginary horizontal plane that runs below
and parallel to the vehicle. Height dimensions are calculated at right angles
from the datum to given control or reference points on the underbody. |
| • | Tram Length refers to measurements that are 2-dimensional and
parallel to the datum line. |
