Section III. FRAME DAMAGE AND MAINTENANCE EXPENDITURE LIMITS

TB 9-2510-242-40

Section III. FRAME DAMAGE AND MAINTENANCE EXPENDITURE LIMITS

3-1

Frame Damage. There are two principal types of frame damage: frame deformation and local damage.

a. Frame Deformation. Frame deformation damages generally are categorized into four types of defects: sway,

sags, twist, and diamond. Often a damaged frame will have all four of the deformation defects. A graphic representation

of each defect is shown in Figure 6. The frames may be checked for straightness per procedure in 3-1(a) 1 through 4.

(1) Sway. Sway is the frame being bent within the horizontal plane. When looking down on a trailer frame it will

show a definite bow. Depending on the direction-of the bow, by sighting vertically along a side rail either its front and

rear corners will be readily visible or the rear corner will not be visible.

(2) Sags and Humps. Sags and humps occur when the frame is bent within the vertical plane. A sag results

when the frame ends have an upward bend. Conversely, a hump occurs when the frame ends bend in a downward

direction. When viewing a frame from the side, in a horizontal plane, a hump will show an upward bow, and a sag will

show a downward bow between the ends.

(3) Twist. A twist occurs when either the left and right sides or front and rear ends of the frame are bent in

different vertical directions. A twist can be easily detected on a flat bed trailer by sighting along the frame horizontally

and seeing all four corners; one front and opposite rear corner are bent up, and one front and opposite rear corner are

bent down. However, twist is not readily visible on SEMITRAILERS fitted with equipment that prevents a horizontal

sighting of all four corners of the bed at the same time. A difference of more than 1 inch between the heights at the front

and rear corners indicates twist.

(4) Diamond. The diamond defect, also called rack, results when one side of a trailer's frame has been pushed

further forward than the other side, and the frame's crossmembers are displaced out of right angles. Use a builder's

square to check all corners. Two or more corners which are not square suggest diamond displacement. A condition of

out-of square 0 more than 1/8 inch per foot of semitrailer length confirms that the frame has diamond displacement

damage. Generally, when diamond displacement occurs, other damage, such as a bent front crossmember or bent

upper coupler supports, exists.

b. Local Damage Cracks and broken welds are categorized as local damage. Cracks are less apparent to the eye

than larger deformations of the frame. Close inspection is often required to find cracks, especially if the frame is dirty.

Broken welds usually start with a crack and eventually turn into a complete separation.

Minor cracks in non-critical areas can be repaired with no detrimental effects on the frame. Repair a cracked or

broken member of a frame by preparing and welding the crack/break and