When the average person thinks of frame or unibody damage they may consider it as a single distinct thing. In reality there are almost countless ways a frame or unibody can be bent. There are also countless variations and combinations of damage.
Because of the variation, frame or unibody damage must be measured to show the extent
Proper frame measurement can reveal the extent of damage. It also allows an expert frame technician to map out a plan of repair. Once the full extent of the damage is thus learned, an accurate estimate of damage is usually possible. Refusing to quote prices before measuring the damage is a sign of a true professional.
A very limited example of frame and unibody damage types follow. You may have seen some of these and not recognized them as frame or unibody damage.
Frame Diamond
When the center box of a straight frame is measured diagonally, the measurements are equal. The center box forms a square. This provides accurate mounting for the suspension.
When one frame rail or the other is pushed out of position, fore or aft, the center box becomes distorted. A diagonal measurement is now uneven from one side to the other, like a diamond. Because the suspension is also affected, frames with a diamond will often show the characteristic "dog tracking." That is they appear to travel down the road at an angle.
Rarely will a pure diamond exist, that is a diamond without other damage. When frame rails move fore or aft, they normally also move out of parallel with the road surface.
Twist
Twist may be somewhat difficult to conceptualize in the mind. It is as if four giants each grabbed a corner of the vehicle. If the two giants at the right front and left rear each pull up and the other two each pull in the opposite direction, the vehicle would twist. This also often happens when vehicles are wrecked or run into a ditch. Looking from the rear, twist is obvious on this pickup truck.
The tailgate of the truck no longer lies in the same plane as the cab. This is because the center of the truck is twisted. The normal symptom is leaning, parts that don't fit and an unstable ride.
Sway
Often when vehicles are hit on one corner, they will suffer sway. This is when the frame rails no longer run parallel to the centerline of the vehicle. A common symptom is a hood overlapping the fender on one side of the opening. The other side will normally have a wide gap.
Very rarely will a vehicle have only one type of damage. For instance, sway, diamond and twist very often exist together. There are many other types of damage as well. For example, sag, bow and crush. The key to accurate frame repair is proper diagnosis. Knowing the full extent of the damage allows it to be reversed, in the order in which it occurs. The frame or unibody has a "memory." The metal wishes to return to the state in which it was form. Properly assisting the metal with hydraulic pressure makes a very clean repair.
When improper techniques are used in an attempt to straighten a frame or unibody, the memory is destroyed. Additional damage is also often caused. Once improper frame work is started, the damage becomes all but impossible to correct properly.
Selecting a frame professional that will measure before any work is attempted is a wise investment. In frame repair, doing it right the first time is not only desirable, it is mandatory. That's what the professionals at AGCO have done since 1974. AGCO will set you straight.
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