Frame terminology:

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 absorb the energy of a collision and protect the passengers.

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 is bolted to the frame. These full frames can be straighten if involve in a collision.

In an accident, the 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 on unibody vehicles that were collapsing in low speed crashes (30 mph) and killing the occupants. These vehicles were previously involved in a collision, and put back on the road again.  A unibody vehicle, with previous frame damage, will have substantially weaken or compromise the structural safety of the vehicle. The only way to determine the structural safety of a repaired frame vehicle, is to wreck the vehicle again, and see if it protect the passenger compartment. Also, there is a direct connection from vehicles with previous accident damage  and chronic mechanical problems. You may 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" estimated that 40% of all accident repairs are substandard. Frame inspections should be performed to determine previous collision damage such as rebuilt or damaged frame channels, frame rails, front and rear frame horns, subframes, floorpans, core supports, upper and lower control arms, valence panels, crossmembers, rust damage, non-factory welds, etc. A frame specialist will be able to tell the buyer if the frame is the same as when it came from the factory. 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 ASE Certified Frame Specialist. The #1 reason vehicles with existing problems are purchased is the buyers' inability to determine the current condition before purchase.