After an accident, many customers are worried that the frame is bent. The truth is there are two different types of “frame” structures on a vehicle and they are very different from each other.
For decades, almost all vehicles had frames that were basically two steel beams that ran the length of the vehicle. The suspension, engine and transmission were mounted to the front of the frame and the body of the vehicle was set on top of it. Frames like this are still used on full-sized pickups and some other types of full-sized cars and vans.
In the early 80s, the unibody type of structure became more popular. It’s basically a series of metal panels that are welded together to form a skeleton and all of the exterior panels are attached to it to form the body of the vehicle. Super high strength steel is used to form parts of this skeleton, making it very strong. Unibody vehicles usually have a sub-frame that is bolted to the unibody and the suspension, engine and transmission are attached to it. It’s usually made of thicker steel, so it has the strength to carry all of the weight and hold the suspension.
Whether it’s a full frame or a unibody, the structure of the vehicle can be damaged in an accident. But don’t worry, it can be repaired, though the techniques have changed over the years.
When a frame or unibody needs to be straightened, the vehicle goes on a frame machine. The vehicle is secured to the machine with either chains or clamps and the damaged area is carefully pulled back out. In the old days (when everything had a steel frame), you could warm the bent area with a flame to soften the metal and straighten the frame back into shape. But excessive heat cannot be used on newer frames and unibodies because the molecular makeup of the high strength steel will be ruined.
When a vehicle is on a frame machine, a measuring system is used by the tech to make sure that the structure is pulled back to factory specs. Targets are hung on various points on the vehicle and computer readouts let the tech know when the vehicle is back in line, down to the final millimeter.
Unibody structures are designed to absorb energy in a crash and sometimes parts of the “skeleton” need to be replaced if they are too badly damaged. But a tech using the right equipment can make your vehicle like new again.
One thing to be aware of though are vehicles with salvage titles that have been rebuilt after a bad crash. If the shop that repaired them heated and straightened out rails that should have been replaced, that vehicle is going to be unsafe. If you are thinking about buying a vehicle with a salvage title, get it inspected before you buy it.