Don’t you just love it when you get your car insurance bill? Have you noticed that the collision part of it can be half the total? If you’ve had an accident recently you’re probably still in shock at the $4000 bill for what you thought was a little fender bender. And what about all those seemingly repairable cars that are "totaled" because the cost of repairing them exceeds their wholesale value?

Modern cars are designed to look good, handle and ride well, and protect their occupants in a serious crash. Believe it or not, all these positives make for one big negative; high cost of repair for accident damage. No one would debate that slick design adds to the cost of repair. Plastic bumpers integrated into the body, streamlined headlights, and curvaceous contours are more easily damaged and certainly cost more than the old steel bumpers, sealed beam headlights, and slab sides of the 60’s. But how does good ride and handling, and crash worthiness, translate to higher repair costs?

In a word: unit construction. Modern cars don't have a separate frame to which the body is mounted. The body is the frame, just like an airplane. This allows the car to be lighter and at the same time stiffer so that the doors don’t squeak and rattle and the dashboard doesn’t shake when the road is rough. The stiff body also allows for better handling. With the movements of the body predictable, the suspension can be tuned for any type of ride and handling desired, even while the car is charging through a corner.

The downside to a stiffer body, besides transmitting more road vibration, is that a stiff body is a killer in a high speed crash.

As Ak Miller, an old Mexican Road Racer, liked to say, "It’s not the speed that kills, it’s those sudden stops."

Ak had it right. If a car hits something at 60 mph it stops, but the occupants keep on going until they hit something. Even if they only hit the safety belt that is a few millimeters away g-forces can be so high that they are killed or seriously injured. The solution, besides the dreaded airbag which in itself can cause serious injury, is to have the car’s body deform on impact, absorbing most of the energy of the crash and lowering the g-forces to levels the human body can tolerate.

I visited Dave Ferguson at Images Autobody recently to see and learn about the latest in unibody straightening equipment. Dave has the CHIEF S21 Pulling System, known in the industry as the "Towers of Power". A picture is worth a thousand words so look carefully at the accompanying photos. Each one of those vertical posts can exert 10 tons of pull. If necessary, Dave can pull in 5 directions at once, precisely reversing the deformation of almost any section of a car. He does it all with that single, hand held control, $40,000 worth of equipment at his fingertips (now you know one more reason your insurance rates are so high). Dave at the button

As Dave worked on the Mercedes 300SL  300SL you see in the pictures (hit on three corners and with a twisted unibody structure) I asked him questions. Some of the answers below were supplied by Adolf Cosio, the CHIEF factory rep who was training Dave on some new equipment.

Jerry Why do you need such an elaborate machine? Why not just cut all the bent panels out and weld in new?

Dave I’ve always straightened cars. I used to use the Kansas jack, a puller hooked to the floor. Everything had a tendency to move. With this machine the basic points of the car are locked and everything can be aligned to them. On the floor you can only pull in one direction. On this machine you can pull in 3, 4, even 6 directions at once. This allows a lower force to be used, which is better because you don’t distort metal you don’t want to.

Jerry So this machine makes it possible to repair cars you couldn’t otherwise repair?

Dave Right.

Jerry Does the CHIEF also work on bent frames like a Chevy Tahoe and bent solid axles like a Land Rover has?

Adolf Yes. It was originally designed for perimeter frame vehicles, back in ‘72. That’s why it has 188 holes in the platform. ramp

Dave I never straighten any suspension parts, including solid axles. I always replace them with new parts. They are under a lot of stress and many have internal parts that must be perfectly aligned.

Ed note: Steel, in addition to being really strong and really cheap for its weight, has wonderful elastic properties and fatigue properties, and great energy absorption properties beyond its elastic limit. That’s why it’s the material of choice for springs. It’s relatively easy to make a car body of steel that is rigid where it has to be, yet easily deformable. All you have to do is put a convex curve in it in the direction in which you want rigidity. You can demonstrate this to yourself with a piece of paper. Hold the paper flat and push it against the corner of a table. It bends with no effort. Now curve the paper away from you in a half circle. Push the peak of the curve against that same corner. Much more resistance. Ribbed panels in station wagon roofs and corrugated roofing are examples of how a thin material can be made very rigid in one direction. By logical extension, if you put a compound curve in that flat sheet it should be strong in multiple directions. Note the arched rooflines and deep side creases on most modern cars. They’re not just for looks.

Jerry How do you start with a car that’s bent 6 ways from Sunday?  Ed note:  Take a look at Dave Klabunde's XK8 that Dave rebuilt better than new Klabunde#1  Klabunde#2  Klabunde#3

Dave You lock the car to the platform with special adapters   clamped  and you measure it. I have a computerized program that has the precise measurements for every recent make and model of car. chart for XJ6 I measure from point to point in every direction measuring front   The dimensions are all in millimeters and each one has a tolerance set by the manufacturer. Usually it’s plus or minus 5 mm. I record all the measurements.

Jerry How do you know how much to pull and in what combination? These charts say nothing about where to hook on and how much to pull.

Dave Based on my measurements I work out a pulling strategy, starting from the center and working to all corners of the car. This is where the science leaves off and the art comes in. After each pull I measure.  diagram from CHIEF of examples of setups for different kinds of damage

Jerry Do you take off all the damaged outer panels first?

Dave No, they stay on until all the pulling is done. I only take off what I need to to get to the pulling points.

Jerry Do you still need to hammer or is everything done hydraulically?  hydraulic tools

Dave No big hammers needed, but you still have to hammer to stress relieve to help the metal back into place. I also use heat, typically 900° F, sometimes as much as 1200° . At this temperature the metal is just breaking its zinc coating, not glowing yet.

Jerry How do you measure this temperature if there’s no glow?

Adolf There are special heat crayons you mark the spot you’re heating. Once the mark starts to melt you’ve got it at that heat range.

Jerry So the main purpose of this machine is to save time and reduce labor costs?

Dave That, and it’s more accurate. Because the car is 30 inches off the floor you can get under it and measure and pull much more accurately.

Jerry Explain some of these accessories that are hanging on the wall. anchor tools  spring compressor

Dave On this board are all the attaching brackets necessary to hook the car to the platform. Some cars have special points put on by the factory. This Mercedes doesn’t, so I have to work from the chart. On this board are all types of hooks and brackets to hook onto the car for pulling. There’s a winch here to pull the car up on the rack and a bellows jack to lift the car

Jerry What kind of training did you have to go through to learn how to use this machine?

Dave I’ve been doing this type of work for 16 years. I go to periodic training courses put on by the factory when I add new equipment to make the work faster and better. My technicians also attend. Adolf is here right now training me on the upper body Universal Measuring System  universal measuring jig  and the resistance welder  over there that duplicates the welds made on the factory assembly line.    spot welder  There is a 24 hour hotline to the factory if I have any questions. If the machine breaks down they’re here immediately to repair it. The whole idea is to make the car exactly as it was built in the first place. Sometimes it turns out straighter than the factory built it. In the future I’ll probably go to a laser measuring system that’s hooked to a computer. That way I’ll get a continuous readout as I pull and I won’t have to stop to make measurements.

Jerry Will this make it more accurate?

Dave No, it just speeds up the work. People get their car back faster and I can do more cars in a given time period.  final step

Jerry Tough question. Can a straightened car ever be considered as good as the original? If the car is in another crash will the occupants still have the same level of protection as a car that has never been repaired?

Dave If the work is done properly, to factory specs, the answer is yes. Some cars, like GM’s, have marks on the structural panels. If the panel is bent beyond the mark it must be replaced. Just because all the outer panels are in perfect alignment it doesn’t mean the car has been correctly repaired. All those panels are adjustable and a "good" body man can move mounting holes, add filler and do any number of tricks to make the outside look right. The only way you can tell is by putting the car on this machine and measuring all the critical dimensions that are specified by the factory. You have to examine all the structural panels that carry the suspension and the suspension itself.

Jerry Is there any law in California or the U.S. that requires a car or its registration certificate be marked if it has had structural repairs?

Adolf No. If a car has been "totaled" by an insurance company that will show up on the registration as "salvage". Some states don’t even require this. Be very careful when buying an out of state car. There is a law in California now that requires any body shop that does structural repairs to have a three dimensional measuring system like Dave has and a four-point anchoring system capable of holding the vehicle stationary during pulls (CA Code of Regs 3351.5). If you’re considering buying a used car, in addition to having a mechanic check it out, you should have it put on a rack like the CHIEF to check its dimensional accuracy and look for any improperly done repairs. Ed note: Carfax Vehicle History Service (www.carfax.com) claims to have a database of over a billion vehicle transaction records. By cross-referencing a vehicle’s VIN they might be able to detect a laundered title, or even a rolled back speedo. Has anyone used their service?

In conclusion So there you have it. It ain’t easy and it ain’t cheap to repair a modern car. But as expensive as it is it’s nothing compared to what it would cost to repair a car with an aluminum or "plastic" unibody.

We all wonder why aluminum and plastic cars have been so long in coming to market. The main answer is that steel is just too good. At a huge increase in expense you can at best save 200 lbs by going to aluminum or plastic and still retain the same crash integrity. And you should check out what it costs to repair an Audi A8 or a McLaren!

Aluminum has lousy elastic and deformation properties and can’t be welded into a unibody that retains its integrity over time. Aluminum fatigues and tears easily. Rivets and adhesives are used to overcome some of these inadequacies. So now we can wonder about the useful working life of the adhesives. The military’s experience with fighter aircraft should give some hints.

I’ve often wondered what the useful life of a unibody made out of carbon fiber and resin is. The long chain molecules of plastics tend to break and unravel over time. Exposure to heat and ultraviolet radiation speeds up this process. Take a look at a fiberglass patio roof that’s been exposed to the weather for a number of years, or the Plexiglas back window of an old Jag factory hardtop and you’ll see what I mean. Some years ago I read a quote from a Lamborghini engineer that in his opinion a carbon tub was only good for 10 years. Wish I could find that article again. I also wonder about old Lotus Elites with their fiberglass unibodies. I know they need continuous repair at the suspension pickup points, but I wonder how badly they’ve deteriorated between those points. Carbon fiber, which is stronger than fiberglass, requires elaborate lay-up techniques and huge baking ovens to produce a crashworthy structure. The costs are astronomical.

I think we’ll see steel unibodies for a long time to come. Check out the Tech Briefs for the month of April 2000 in the S.A.E.’s online magazine, Automobile Engineering International, at their website, www.sae.org. Go to the sitemap to locate the magazine. Read the article, "Automotive Dieting"