A car’s frame is more than a simple skeleton on which we hang the body and suspension parts, it is like the foundation of a house. If a car’s frame is bent, weakened, or not aligned properly, not only will the restoration be flawed, the car may well be dangerous to drive.
The tricky problem is that frame damage is a lot harder to identify than body damage. In most cases, the frame is concealed when you’re considering making a purchase. The seller may not know about old frame damage, especially on older cars, and the frame may have been repaired incorrectly.
Another challenge with older cars is that modern frame tools are computer-driven, and the alignment points of modern cars are held in a database, so that the technician need only attach the alignment lasers to specified chassis locations and the computer will reveal any misalignment. Data for classic cars is not generally included in these databases, so some very modern frame shops may not be equipped to detect frame damage on your car.
But the good news is that the frames on older cars are generally much simpler than on a modern multiple-stamping unibody design. Using simple tools and basic measurements, an experienced frame technician can detect bends, twists, warps, and general misalignment, and repair these faults with relative ease. Some commonly-used frames such as the Ford Model A, are being reproduced and can be purchased new. In extreme cases, some unobtrusive bracing can re-strengthen a damaged frame.
There are generally two types of chassis design: ladder frame and unibody. A ladder frame is so-called because it resembles a ladder. Two parallel longitudinal frame rails connected by lateral cross-members provide the basic structure of the vehicle. In a unibody design, the chassis is stamped from sheet steel and welded together with the main bodywork for structural stability. Some cars, such as General Motors products, use a hybrid form with a central unibody passenger compartment combined with separate front and rear ladder frame “clip” sections. Virtually all modern street cars smaller than the largest sedans are of unibody design.
Many older frames are made of simple C-shaped steel stampings, held together with cross-members of the same material. Many of these early frames were held together with hot rivets rather than welds, which allowed them to flex a great deal. While these frames are apt to be misaligned, the good news is that they can be re-aligned.
If there is rust damage, your frame needs to be carefully evaluated. If the rust is localized, you can have the rusty portion cut out and replaced with a new piece. “You have to remake a new piece. These frames are generally tapered; they’re not a rectangle, they’ve got shape to them. You weld it in and the grind the weld smooth,” says Russ Nyberg of Racetech Fabrication in Portland.
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While it is possible for an amateur to measure and repair frame damage, the critical nature of the component, the relative difficulty and expense of making repairs after the restoration is complete, and the relative ease and low cost of inspection and repair during the first stages of the restoration process all make the case to take your frame to a professional for inspection and repair. Since you will likely have your frame stripped and painted, this step is simple and easy insurance.
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Finally, when your frame is clean, straight, strong, and true, you’ll want to paint it as soon as possible to prevent rust from forming. For the purest restoration, paint it in the same color and with the same materials used by the original factory. To hide light rust pitting, signs of welding, and other repairs, some restorers will have a frame powder-coated, and then painted with the original color as a top coat. This provides maximum long-term protection and a great finish. “If it’s anything less than a 100 point show car, go for the process that will give you the best longevity. And that’s powder-coating,” says Bob Earls, owner of Webfoot Restorations in Portland.
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DO |
- Take the time to have your frame inspected and measured by a professional
- Check rivets and welds for structural integrity
- Have all repairs performed by an experienced frame technician
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DON’T |
- Don’t ignore buckles, broken welds, and other signs of previous damage
- Don’t use a frame that has been compromised and repaired incorrectly
- Don’t simply paint a frame and assume it is fit for use
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The previous owner of the Popular Restorations feature car said the car had never been in a significant accident. The disassembly process gave me no reason to doubt him. Although the frame is a whopping 18 feet long it is incredibly rigid, so I skipped checking its alignment.
Why is the frame so rigid? Take a look how it is reinforced with a huge x-brace that is welded and riveted to the side girders.
The x-brace is 3/16” thick as are the side-girders which are also boxed from the x-brace forward and back.
So I felt reasonably safe just having the frame sandblasted and powder coated. One lesson I learned was to take plenty of photos of all the small clips and other fasteners that hold the gas and brake lines, emergency brake cable, and wiring to the frame. I thought I had done a fairly thorough job in that regard but ended up needing to look at another Packard to figure it all out.
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Scott Olsen
Professional Frame Inspector & Certified Frame Repair Technician
Kelso, Washington
(Scott doesn’t take private clients)
Scott Olsen has 20 years of experience as a certified frame technician and is employed by Manheim Auctions as a frame inspector at the Portland Auto Auction. His experience includes many restorations of both traditional ladder frame and unibody design chassis. We asked him to talk about the details of frame inspection and repair.
PR: How can someone tell when a car’s frame has been bent or damaged?
SO: There are often clues that a car has had previous damage, such as a fender replacement or older body repairs. When you find a clue like that, you should take a look at the frame. A lot of times with much older cars, they’d be in an accident and they’d be repaired, and our ability to repair frames was not as good back then as it is today. They’d do the best they could, but they couldn’t fix a frame the way we can today.
Checking the body first for signs of previous repairs is the first thing you want to do. But if the car has already been dismantled and you don’t have the body, or if you just have a frame, you start with a visual inspection of the frame and you look for symmetry. Most frames are symmetrical -one side is exactly a mirror image of the other side. If something doesn’t look right, look for visual damage such as signs of buckling. Buckling happens when something has been bent and pulled back out. Especially with older repairs, they often didn’t take the time to do cosmetic repairs on the frames, so there’s visual evidence that a frame has been damaged and repaired.
Also, during a restoration, you might take the car apart and find a frame that has been damaged and repaired properly, but maybe you want to do a better job of that repair.
PR: What does frame damage look like?
SO: It depends on the type of damage. There are common types of damage and then damage that’s less common. Probably the most common damage I run across is sway damage. That happens when the front or rear of the vehicle is hit with a side blow. If there has been a side impact at the front bumper, it would sway the front frame rails over. In older vehicles, there was a lot of forgiveness and adjustability built in. So shops could adjust a little bit of side sway out in the sheet metal, but in a restoration you’ll want to fix it.
Another type of damage is a twist. That’s when one rail or the other goes up or down, that can cause the frame to twist. There are different degrees of severity of twist. Twist can be isolated to one end or the other, or it can be in the center of the frame, which affects both ends. That’s a severe twist. A lot of times with old repairs, the frame technician didn’t realize that the twist was in the center section, and they’d repair both ends and get the sheet metal in pretty good shape, but the damage is still there.
Another damage condition is diamond. That’s when one rail is moved forward or back in relation to the other. For example, if you hit something right on the end of a rail, like running into a phone pole, it will move that rail back in relation to the other. When that happens, it causes sway to occur in one direction at the front of the vehicle, and in the opposite direction at the rear. If a technician didn’t realize that there was a diamond condition, he would pull the sway out in the front and in the rear, so the frame rails are parallel, but one is further back than the other. That’s something you want to correct before you move forward with your restoration.
PR: How do you fix these problems?
SO: It’s all about analyzing the problem and using a proven repair to fix it. If you bring me a frame from any kind of restoration project and you’re suspicious about it, we determine if there’s a problem by measuring it. The old-fashioned way is to use tape measures and mechanical frame gauges. A tape measure or tram gauge can tell you if there’s diamond in the frame. You can measure the center torque box under the passenger area of the frame, the front torque box where the engine sits, and the rear torque box where the rear end and trunk are normally located. We cross-measure the center torque box and if the frame has diamond, it will show up in that measurement.
You can also cross-measure the front or rear torque box, looking for side sway. If there’s sway one way or the other, it will show up in a cross measurement. Twist won’t show up with a tape measure. You have to hang old-fashioned slider gauges on the frame, and then twist shows right up.
With an old frame and the older measuring equipment we have, it’s very possible to correct these conditions. You don’t have to have the very latest equipment to do a good job.
PR: Older cars are known for having weaker frames, should they be reinforced?
SO: Most of the restorations I’ve been involved in, the car will lead a very pampered life after the restoration, and people want the frames to be original, so it’s never come up.
PR: Tell me about the process of making the actual corrections?
SO: Let’s assume that we’re getting started on a frame project. The body’s been removed, but the frame still has the suspension and wheels on it. We know it has had damage because we can see a previous repair or a buckle in it. The first thing I do is put the frame up on the bench and completely measure it to the best of my ability. The best case is that we find that there’s no damage -just buckles left in from a previous repair and the technician did a perfect job of pulling the frame. Then we just do the cosmetic repair necessary to remove the buckles. That’s the best case scenario.
The worst case is that we find hidden damage such as diamond and twist in the center of the frame, and the front and rear torque boxes were pulled back into shape to get the car back into service. Now we have to repair the twist and diamond in the center, and we have to re-repair the front and rear ends of the vehicle as well.
So, if we determine that there’s diamond, we will chain one frame rail down to the bench and block it up with wooden blocks so it can’t move around. Then we pull the other frame rail forward or back until the center torque box measures square again. For twist, we’ll chain down all four corners of the center torque box and block it up with wood. So all four corners are up on blocks and chained down to the bench. If the car has twist, we leave a block out of the high corner, and we can pull on that frame rail and pull that corner down. That removes the twist from the frame.
PR: How about Unibody cars?
SO: On unibody cars, crash damage is generally more isolated. It doesn’t transmit through the vehicle as with a conventional frame, so there’s usually no twist or diamond throughout the entire vehicle. In these cases, you can use a laser system in absolute mode to detect damage, which you can then repair.
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| Click on any item below for more details at Amazon.com |
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Herb Adams
Chassis Engineering HP1055
HP Trade, Paperback, 1992-11-19 |
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Like most books on chassis construction, this one is aimed at the racing community rather than the restorer. However, if your restoration involves significant chassis fabrication, there is a lot of good technical detail in this book.
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Steve Smith
Advanced Race Car Suspension Development
Steve Smith Autosports, Paperback, 1994-10 |
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This well illustrated book explains the basics of race car suspension and chassis design. Weight transfer, roll couple, and structural stiffness are explained in-depth. It includes formulas and a math section in the back. Written from a circle track perspective.
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James E. Duffy
Collision Repair Fundamentals
Delmar Cengage Learning, Hardcover, 2007-03-21 |
This textbook was written and illustrated to introduce readers to automotive collision repair. Collision Repair Fundamentals stresses the repair of minor body damage and repainting, as well as advanced repairs such as frame straightening and structural panel replacement. Each service-oriented chapter is accompanied by a practice ASE test featuring numerous ASE-style questions.
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Jeffrey Zurschmeide, Russell Nyberg
Automotive Welding: A Practical Guide
S-A Design, Paperback, 2009-05-15 |
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This book was written by our contributor, Jeff Zurschmede. Besides being informative and comprehensive it is extremely well organized and illustrated. The following topics are presented in a straightforward manner with plenty of color photos: the kinds of welding and metalworking available, the tools required to perform welding tasks, the types of welders available, basic welding techniques, grinding and cutting, various forms of sheetmetal work, frame repair and reinforcement, filling body holes and rust repair, tube-steel projects, and more.
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