More and more vehicle owners are hitting the roads in their 4x4s, so it's important for technicians to understand the basics when it comes to repairing these vehicles.
While repairing all-wheel drive vehicles, such as light trucks, full-size trucks and SUVs, entail many of the same procedures as their car counterparts, you must heed certain procedures and precautions unique to 4x4s when returning these vehicles to pre-accident condition.As with any vehicle, damage assessment is the first step in ensuring a quality repair. A technician can see how far back or far forward the damage occurred by visually checking the sheet metal, says Bob Meinert, advertising director and spokesperson for Alexandria, Minn.-based Chassis Liner, which manufactures frame racks and other repair equipment. For example, a Chevrolet Suburban is a full-frame, six-door vehicle with many body and door gaps. From the factory, these gaps are uniform and can signify how the impact has affected other parts of the vehicle if there is a variance. "Often times, comparing an undamaged side of the vehicle to the damaged side is a tell-tale sign of where frame damage has occurred," Meinert says.These gaps are just the obvious visual references, but when the underside of a 4x4 vehicle is examined, much more can be determined. Wrinkles, buckles and diamonds in the rail are obvious damage points, but using measuring gauges or a 3-D measuring system helps determine the damage along a vehicle's structure, Meinert says. "Comparing the length, width and height measurements of the damaged truck against measurement data sheets tells you exactly where the structure needs to be pulled to correct the damage," he says.Full Frame vs. Unibody in 4x4 RepairIn addition to keeping in mind that there are two types of construction- unibody and full-frame (perimeter frame) -that must be considered when repairing 4x4, or all-wheel drive, vehicles technicians must understand the difference.The I-CAR Tech Centre makes several suggestions for the repair of full-frame vehicles, specifically focusing on crush initiators, sectioning recommendations and straightening issues, as well as the use of heat in repairs and the reinforcement of cracks.Crush initiators, which help manage collision energy, are designed within collapse zones that absorb some of the energy during a frontal collision. The initiators, which combine with such in-frame features as kick-up areas or offsets, are made to direct the energy of a collision around the passenger compartment.On full-frame vehicles, such as 1996 and newer Ford Explorers and Ford F-150s, the crush initiators do not have near the same physical appearance as the more exaggerated convolutions found on earlier frames, according to I-CAR. I-CAR stands by this rule on the repair of these 4x4s: Do not repair crush initiators. "This area is from the front to about 600 mm (24 in.) back," I-CAR full-frame repair material states. "If the frame is bent in this area, straightening is not an option."General Motors (GM) introduced a new full-frame design for its 1999 and newer 1500- and 2500-series pickup trucks and for 2000 model full-size SUVs, and all of them have crush caps that must be replaced if the crush zone portion of the caps has collapsed. The looped-out portion in the front on the bumper bracket and the raised portion between two step flanges are the crush zones on these parts, according to I-CAR. If these parts are only scratched or nicked, it is not necessary to replace them.Ensuring a Good FitIt's also imperative when working on 4x4 vehicles to make sure the vehicle will fit on the frame-straightening machine. This is especially important because these vehicles have larger frames than typical cars and because there is such a variety on the market. "Modern day frame racks need to be versatile enough to handle all types of vehicles, regardless of their design, unibody or full frame," Meinert says. "Body shops find that the frames of current trucks and SUVs are more difficult to pull than ever before. Steel is more rigid, and frames are more complex." Pulling a full frame on a 4x4 vehicle takes much more force than when pulling a 4x4-unibody vehicle, Meinert says."Some of the pulling machines are not long enough to pull full-frame SUVs and full-size pickups," says Rhody Hayes, an autobody technology instructor at Pasco, Wash.-based Columbia Basin College and a former autobody shop owner. Attempting to fix the vehicle on a pulling machine that is not large enough will only hinder the repair process, and could cause safety problems. "There are a lot more safety-related problems when you're dealing with a full-frame vehicle," he says, explaining that repairers run the risk of dealing with breaking clamps, problems with chains loosening, etc.This is why multiple pulling, as well as having the ability to pull 10 tons, is essential when repairing these full-frame vehicles. Making multiple pulls simultaneously puts less stress on the metal, Meinert says. Back anchoring is also important. "When using more force to correct damage, localizing the pull to a specific area allows for less movement away from the pulling area, making for a better repair," he says.AnchoringBecause accident energy is designed to travel through the vehicle, technicians must use a frame-anchoring system designed to repair the five main types of damage-diamond, side-sway, mash, twist and sag-to ensure proper repairs, says Susan Hoffmann, marketing manager for Blackhawk-KJ. "The frame-anchoring system should have positive jaw holding power that mounts directly to the vehicle rail," she says. "Plus, you want to look for a frame-anchoring system with a three-way adjustment-length, width and height-to swiftly position the system and secure the vehicle."Hoffmann says this type of frame-anchoring system is easier for the technician because he or she doesn't have to do miscellaneous work, such as removing tires.Ken Olesen, product specialist and instructor for Chief Automotive Systems, echoes her advice, adding that "anchoring is important to make it easier to pull [the vehicle]." He also says that using a positive anchoring system, or solid anchor system, should be used instead of chains and blocks. This type of system attaches directly to the vehicle. A fast anchoring system may also be used. This system attaches to the machine, as well as directly to the vehicle, to make a positive link between the two.It's also adjustable. This aids in the repair process if a vehicle has a diamond-when the center section of the vehicle is out of square and one rail has been pushed back further than the other-because repairs can be made more accurately.Frame StraighteningA misaligned frame can be fixed by straightening the out-of-line parts or by replacing the crossmembers, braces or brackets if they are badly damaged. Straightening should be attempted on frames that do not meet specifications of the diagonal checking method or where damage is visible, according to I-CAR. But only parts that are not severely bent should be straightened. This is to prevent internal stresses in the metal.GM advises keeping the temperature below 1,200Latest in Operations
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