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4 Structural Repair Laws to Live By

Many of us still rely on the might of the hammer and the sweat of the brow to return a twisted pile of sheet metal back to a safe and serviceable vehicle. But you can reduce that sweat by using a little common sense and applying a few laws of physics.

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Contributing Editor Keith Combs is the body shop manager at Bill Roberts Chevrolet, where he’s been employed for more than 25 years. He was named GM/ASE Master Collision Repair/Refinish Technician of the year in 2000 and was one of the first to achieve GM’s World Class Technician status in 2002.

When you hear the phrase “structural repair,” what do you think of? Elaborate laser measuring systems? Frame repair racks that incorporate multiple towers and are computer controlled from a safe distance? Racks that are so easy to use, they’re as simple as playing a video game or loading a program?

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Point, click and the damage is gone.

People with thoughts like those probably have never repaired automobiles like you and I have. Even I’ll admit that I’ve entertained daydreams of manufacturing a machine that simplifies the tedious chore of returning a twisted pile of sheet metal back to a safe and serviceable transportation unit. Then I realize I’d be more productive if I’d think about how to repair the job at hand.

Still, such advanced equipment may not be so far from reality. A few of you reading this may even be asking “Where has this guy been? I have such a machine.” If you possess equipment that eliminates the thought process and common errors, this article isn’t for you. (However, I bow to your superior equipment and promise to send all of my frame repair work to you.)

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This article is intended to educate those who still have to use the might of a hammer and the sweat of the brow to repair these modern chariots. The good news is, you can lessen the sweat by using a little common sense and by applying a few of laws of physics.


Law No. 1: Measuring is the basis that all good structural repairs are based on.

I’m not proposing that we go back to the days of using a plumb bob and chalk on the floor to plot out the damage, but using that method to train a novice isn’t such a bad idea. Using primitive methods sometimes illustrates the actual process more effectively, giving us a better understanding of the damage. And that’s the key to repairing structural damage: understanding what’s wrong.

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To determine what’s wrong, you need good measuring skills. I’ve seen inexperienced (I use the term inexperienced because it’s the nicest word I can think of) technicians pulling the pointers of a tram gauge out of shape to reach a hole instead of pulling the hole to the point it belongs. Obviously, these technicians have little grasp of why we measure.

I keep stressing the obvious because I’ve seen too many occasions where the obvious seemed just out of reach. I’ve had inexperienced technicians come to me and ask, “I can’t get that car to pull, what do I do?” I usually ask them what the frame gauges indicate, and they often shrug and tell me, “I haven’t hung them yet.”

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Some people think you don’t need to bother with the gauges and measurements until you get “close,” but I feel the opposite is true. If you make a pull without finding the problem first, you’re wasting your time. I won’t dwell on this subject too long, but I must add that most mistakes in structural repair are made by not dwelling on measuring long enough.

When I say measure, that incorporates many things. When you make your preliminary inspection, you’re visually measuring the gaps for unevenness. When you open and shut the doors, you measure the force required to operate the doors for any abnormalities. When you stand back and observe the stance and attitude of the vehicle, you’re visually measuring sag and sway. These are just a few of the so-called “seat of the pants” measurements that lead you in the direction to actually put the tape (or laser) to the car where it needs it.

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Keep in mind that you probably won’t be measuring every measurable point on the vehicle, although that would be ideal. If you did, you wouldn’t need a hobby because this process would occupy all your spare time. You’ll probably never find anyone who’ll pay you to check every point either, so you must determine the priority spots to maximize your time.

Sometimes, even when you think you’ve measured and repaired everything, something still isn’t quite right. Such a problem was illustrated to me recently when a customer brought in a used vehicle he’d purchased and pointed out that it didn’t sit level. The full-frame vehicle showed signs of previous body and frame repair of respectable quality. We started a systematic approach by first putting the vehicle’s center box on stands to eliminate the chance of a weak spring causing the awkward-looking stance. We then installed the centerline gauges, which showed nothing suspicious. Thinking the springs must be the culprit, we eliminated that variable by switching the front and rear springs from side to side – still no change. Determined not to let this vehicle get the best of us, we investigated further.

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The technician working on the vehicle had initially thought the left front spring pocket might be suspect. After measuring the heights, he determined it to be within tolerances. But a more thorough inspection yielded a clue. The left front control-arm adjustment cam had reached its outermost position. We checked the camber, finding it to be barely within tolerance with no adjustment left. That indicated to us that the frame rail was rolled in at the top (given that the bottom of the rail had previously measured true). After correcting the roll in the frame and doing a proper alignment, the vehicle sat square and true again.

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Although we hadn’t performed the original repair, I felt just a hint of egg on my face because I hadn’t looked hard enough for that adjustment cam that was abnormally to the end of the adjustment slot. This situation shows that common sense is a measuring tool that does as much good as anything else we have hanging on the wall. Use yourt common sense liberally, along with determination and the best tools your budget allows, and you’re assured success every time.

Law No. 2: Pulling and stress relief are two different things you need to do simultaneously.

When I say pulling and stress relief are things you do simultaneously, I don’t mean pulling out your hair to relieve your stress. (Although to look at me you can tell I’ve done my share of that.) What I mean is that while you have pulling pressure on the vehicle, find the buckles with damage locked in and relieve the stress by tapping the high spots to help flatten down the buckles. I said tap, not crush. Use judicious force – you can do more damage than good if you get carried away.

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If you’ve set up a pull and it seems like you’re beating your head against the wall, you probably are. I’ve often seen pulls set up without regard to the simple laws of physics. If there’s a buckle in the side rail, the rail is probably also shorter. A buckle in a rail may appear to need a pull straight from the side. Evaluate the possibility of setting up a pull that will effectively lengthen the rail as you pull the buckle outward, giving you the advantage of leverage as well as the brute strength of hydraulics. Remember, for every action there’s an equal and opposite reaction. That rule will always be a constant.

You’d do well to imagine a pull set up like the opening break shot on a pool table. When you put pressure on the buckle, where do those forces spread from the direct point of pressure? When you “break” in pool, that force spreads balls in different directions, depending on the placement of force. Change the direction of the force, and the balls radiate in a different direction. Change the direction of a pull, and the same applies to frame repair.

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Think of angles and effects of angles on the pull. The rail wants to go back to its original shape, so if you’re helping with the proper angle of pull, the rail will cooperate. If the angle of the pull is incorrect, you’ll find an undue amount of pressure is needed to see any change. When the angle of pull is correct, it’s surprising what little pressure is needed to persuade things to come back to where they belong.

One last thing in reference to pulling is to spread the force out to keep from tearing or crushing. If you think one chain (or clamp) is “good enough,” see if two won’t work better. The more attachments you make, the more leverage you can control and distribute to help the vehicle go back into shape. There’s a saying that we often use in our shop: Less is more and more is less, which reminds us that a little extra effort sometimes saves a lot of effort in the long run. On the same token, sometimes doing less effort can necessitate more effort in the end.

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That saying also applies to attachment points when pulling. Even on minor pulls, I’ll try to hook to as many points as possible to minimize distortion from too much localized pressure. Not only are you pulling with the chains from the posts, but the chains and blocks used to hold the vehicle are also making pulls. The chains act as levers to pry the damage our way, while the blocks (or stands) act as the fulcrum point to change our leverage multiplication effect.

Law No. 3: Welding is the glue that holds it all together.

When doing structural repair, you’ll need to do more than an occasional weld. Welds should be performed to duplicate as closely as possible the original strength that was designed into the vehicle. I don’t recommend you try “out-engineering” the engineers. They design these vehicles with the protection of the passenger in mind.

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When you see five welds in a flange, you should make sure five welds are put back in that flange. Just about all of us understand that we don’t want to make a vehicle weaker, but some of us don’t understand that we don’t want to make it stronger either. Crumple zones are built into vehicles to control crash forces. Don’t change their characteristics by adding or doing away with welds. Always try to replace any parts at the original factory seams, using welds that simulate the integrity designed into the structure at hand.

The quality of the weld is also a major consideration. Practice on similar scrap steel before moving on to the vehicle. It doesn’t matter how many or how few welds you have; if you don’t have quality welds, it’s all in vain.

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I used the word glue earlier in this article, but we don’t rely on glue when we talk about structural repair. Some day, glue may be the only accepted method of attaching unibody panels together. For now, welding is the only method that should be used in structural repairs.


Law No. 4: Common sense is the key to it all.

As you read this, you’ve probably noticed that I have simple thoughts. I don’t consider myself overly smart, yet things seem to go well for me when doing the day-to-day duties required of today’s collision technician. Common sense and dedication are your first and foremost friends in all you do here. If you have those, the rest comes easy.

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Measure and understand what the measurements indicate. Pull and stress relieve the unibody back into its original shape. Duplicate the strength of the factory welds when replacing or repairing the unibody. After you’ve measured twice to ensure all things are in proper relationship with everything else concerned, tack weld your parts and measure once more to ensure no chance of error.

You will, no doubt, work with many people who tell you if they only had the right “tools,” they could fix a certain problem on a car. Granted, you do need a minimal amount of tools, but you should first rely on your God-given ones. I can recall individuals who were masters of this trade in our area. They were always placed on an almost mythical pedestal, heroes in my mind so to speak. Tales of their abilities to repair frames with a rock and a string were grossly exaggerated because of their superior abilities to use their most valuable tool: the mind. We all can only hope to achieve such reverence these local heroes have acquired. I’ve met many of these men, and none had any real physical attributes that set them apart from the rest of us. Their only real advantage was their ability to think at the same level as the damage.

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I’ve worked with many technicians over the years, and I have yet to recall a single one who hasn’t added to my education of the trade in at least some minor way. The thoughts compiled in this article are a cross-section of things they’ve taught me, along with experience and knowledge shared from teachers and authors of previous articles. I realize the content here is simple, but that’s the point.

Writer Keith Combs is the body shop manager at Bill Roberts Chevrolet in Bolivar, Mo., and a GM/ASE Master Collision Repair/Refinish Technician of the Year. He’s been in the collision repair industry for 23 years.

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