Body-on-Frame Construction: Most heavy duty trucks and a few premium full-size cars are still manufactured with a body-on-frame construction. This is a manufacturing process which a weight-bearing frame is welded together and then the engine, driveline, suspension, and body are bolted to the frame.
Unibody Construction: Most vehicles today are manufactured with a Unitized Body/Frame (Unibody) construction. This is a manufacturing process where sheet metal is bent and formed then spot welded together to create a box which makes up the structural frame and functional body of the car. These vehicles have "crumple Zones" to protect the passengers in case of a collision.
In an accident, a unibody frame is designed to "crumple" and absorb the energy of an impact better than a Body-on-Frame construction. However, the unibody frame was not designed to take more than one accident
The news magazine "60 Minutes" reported vehicles with unibody frames that were collapsing in low speed accidents (30 mph). After an investigation, these vehicles were shown to have had previously frame damage. A unibody frame vehicle, with previous frame damage, will have had substantially weaken or compromise the structural integrity of the vehicle's frame. The only way to determine the structural safety of a repaired frame vehicle, is to wreck the vehicle again, and see if it survives.
Also, there is a direct connection from vehicles with previous accident damage and chronic mechanical problems. We hear of people complaining that their car (Ford, Chevy, Honda, Toyota, etc...) has chronic mechanical problems. Many times these chronic mechanical problems can be attributed to some past accident and un-repaired or un-repairable frame damage. Farmers Insurance Corp. estimated that 40% of all frame repairs are substandard.
In addition to the structural and mechanical concerns listed above, a previous wrecked vehicle will be worth less then a non-wrecked vehicle of the same type. This is called "Diminished Value"
A pre-purchase inspection should include a frame inspection performed by Certified Frame expert. An inspection should determine any previous collision damage such as rebuilt or damaged frame channels, frame rails, front and rear frame horns, sub-frames, floor pans, core supports, upper and lower control arms, valence panels, cross members, rust damage, frame alterations, non-factory welds, etc. A Certified Frame expert will be able to tell the buyer if the frame is the same as when it came from the factory or, the the extent of any previous accident damage and the quality of any repairs.
Most automotive technicians have little or no experience in frame analysis or repair. There is big difference between a mechanical technician and a body technician. Rarely will you find a shop that has ASE Master Technicians and ASE Certified Body and Frame Technicians under one roof. Before purchasing, be sure to have the vehicle's frame professionally inspected by a Certified Frame Specialist.
Every Auto P. I. Inspector is a ASE Certified Master Technician for the mechanical and electrical systems and is also certified in Body and Frame Analysis. This combination of Master Technician and Frame Analysis make our Inspectors some of the best qualified technicians to perform pre-purchase inspections.