Collapse
The frame may appear out of alignment under certain conditions when another condition exists. Refer to Checking Frame Alignment .
The condition that occurs when buckles appear on more than one surface of the box section of the side rail. Collapse is the condition that occurs when a section of the underbody or the frame structure has been shortened in length.
Diamond
The condition where 1 side of the frame moves forward or rearward. The diamond then causes the frame structure to be out of square.
Sag
A vertical misalignment that results in an incorrect datum line. Kick-up occurs when both sides of the frame are equally misaligned.
Sidesway
A section of the frame positioned to the left or right of the centerline when compared to the rest of the vehicle.
Tracking
The alignment of the vehicle's axles with each other. A misaligned frame can cause improper tracking. All the axles will be parallel to each other and all the axles will be perpendicular to the centerline of the frame when the vehicle is tracking correctly.
Twist
The condition where the sides of the underbody plane, datum, are not parallel. 1 rail slopes up while the other rail slopes down.
