Frame Fundamentals: When to Restore, When to Replace

It’s called a “frame-off restoration” for a reason. It signifies the ultimate rebuild. The car is taken apart as far as you can go—all the way down to the very frame. That’s where the car began when it was built, and a proper rebuild begins with the frame as well. This brings us to a fundamental question: When can—or should—you reuse, repair and or restore the original frame? When should you buy or build a new one? And how much frame do you need for the performance level you plan to build?

“Determining when to replace a frame depends on a variety of factors, one being the desired level of performance,” said Nick Gregson of Classic Industries in Huntington Beach, California. “If you’re building for high performance with an emphasis on handling, then the original parts may not be up for the job, even if they’re in perfect condition. However, if the builder’s intent is to maintain originality, this may not be the case."

The customer also plays a part.

“Sometimes it’s valid to rework an original frame and sometimes it isn’t,” said Brent VanDervort, president of Fatman Fabrications in Charlotte, North Carolina. “The answer depends on the question and the question depends on the customer. That’s the only honest way to look at it.”

Re-framing the Question

Less inscrutably, the question that depends on the customer is the customer’s intended use for the vehicle.

“Some frames are going to be just fine for a certain use,” VanDervort said. “The other major factor is condition, what Mother Nature did to it or what some hot-wrench butcher did to it. If it’s been cut up, or it’s just plain rusty, either way it’s beyond economical repair.”

VanDervort cited a recent experience at his shop as an example.

“A guy came in who was building a 1952 Chevy pickup and [he asked if he needed a new frame]," he said. "We asked what he wanted to do and how much he wanted to spend. And it turns out that all he wanted was a nice driver and that the frame he had was in good shape. It made perfect sense to modify the original frame. This customer didn’t care if it had pits in it, or if it was painted black with a rattle can."

“But then you have another customer who wants a car that looks as nice on the bottom as it does on the top,” VanDervort continued. “He’s going to put more horsepower in it and he’s going to drive it harder so it starts to make sense to consider a new frame.”

Gregson of Classic Industries advised builders to examine the condition of the welds, the amount of fatigue in the metal, how much rust is on it and how far it is out of alignment.

“If the labor cost to fix the original exceeds the cost of replacement, then replacement should be strongly considered,” he said.

Tony Bicknell of RideTech in Jasper, Indiana, pointed out another potential problem.

“Along with the obvious rust and collision damage, you have to pay attention to crossmember sag,” he said. “We hear from a lot of customers who have trouble getting a proper alignment, and in a lot of cases it’s because of sag. Years of driving can cause the crossmember to bow, pulling the frame rails in toward the motor."

“[That's not] the end of the trail for your crossmember,” Bicknell continued. “This is when you will find out how good your alignment shop is. If the materials are still in good, serviceable condition, you can put the car on a frame alignment machine, block it and pull it back down, then align it and you’re back on the road."

“But if the condition of the metal is in question, or if the car has sustained collision damage, it may be a good idea to consider replacing or even upgrading the frame or subframe,” he added. “There are several reputable companies that produce quality subframes that are engineered and equipped with modern brakes and suspension geometry.”

Justin Padfield, owner of Scott’s Hot Rod Shop in Oxnard, California, recommended replacing any frame from 1960 or earlier.

“By the time our customer gets the car, it has frequently passed through 20 other people and the frame has already been abused, neglected, modified or altered,” he said.

“When you start upgrading a stock frame with aftermarket suspension parts, body mounts, etc.,” you’re going to add up more cost in parts and labor than if you bought a complete new rolling chassis, Padfield said.

“The best deal for your dollar is a new tube chassis," he said. "We use boxed rails with .120-inch wall thickness and a 1-½-inch tubular X-member with a wall thickness of .125 inches. It’s all mandrel-bent and 100-percent TIG-welded. It’s strong enough to handle 1,600 horsepower [even though] you’ll never use 1,600 horsepower on the street."

Go for the Show

“If the customer wants a show car then we are not going to use a stock chassis at all,” said Padfield. “We’ll build a new, modernized chassis with frame rails that fit the body, so the gaps are all consistent, and it’s all laid out with precision and looks correct.”  

VanDervort of Fatman Fabrications agreed that a new chassis is almost essential for a show car build.

“If you are going to build a show car, it makes no sense to use an original frame,” he said. “A lot of things like sandblasting used to be pretty easy and inexpensive to get done, but not so much anymore. Probably half of it is [because of] environmental regulation. It used to be that you could get a pretty good sandblast for $100 or $200; now it’s more like $500 or $600.” 

For strictly stock (or stock-appearing) restorations, Classic Industries now offers reproduction front subframes for 1967–1969 Camaros and Firebirds, with individual part numbers for each model year.

Gregson called them “a cost-effective alternative to attempting to repair an original front subframe that may be internally compromised.”

The company’s new reproduction subframes feature factory-style welds for an OEM appearance, but have extra bracing hidden in the lower crossmember for added strength.

This added reinforcement is completely invisible from the exterior, said Gregson, who said that each subframe comes with all the same holes and brackets as the original.

Planning for Power

Heidts' PRO-G front subframes are complete, bolt-in replacements for the factory originals.

Perhaps the most compelling reason to replace an original frame or subframe is that you're building in more power and performance than it was designed to handle.

“Safety is the driving criteria,” said Kenny Brown, an engineer at Heidts Hot Rod & Muscle Car Parts in Wauconda, Illinois. “If you’re adding more horsepower, or even just installing a new motor, you almost have to upgrade everything.”

That applies, somewhat surprisingly, even to classic muscle cars, which we usually assume to be designed to handle high levels of horsepower.

“Actually they weren’t designed for high horsepower, just for a lot of torque,” said Brown. “The new engines available today are a lot more powerful, and the aftermarket is making them more powerful still. Almost any contemporary motor is going to make more power than a classic muscle car was designed for.”

How can you determine how much frame you need for how much horsepower?

“It’s not a calculation, it’s experience, and for someone trying to learn it, there is no easy guide," said Fatman Fabrications' VanDervort. "You want to look at cornering power, too, because that can put more stress on a frame than horsepower. Any new frame we build is going to be stronger than the original.”

More importantly, he added, strength can be achieved through good design, and just by “throwing locomotive weight at it," VanDervort said. “We build all our frames out of .188 wall steel, which is pretty much the industry standard whenever you’re worried about strength.”

“If the goal is Pro-Touring, then even a reproduction of the original isn’t ideal for high-performance cornering,” said Gregson of Classic Industries. “A custom-fabricated subframe is a better option.”

“If the car is being built as a legitimate hardcore track car, then upgrading the frame is a given,” said Bicknell of RideTech. “The largest benefits are additional roll stiffness, corrected and updated suspension geometry, and installing a structure that’s engineered specifically for high-performance steering, brakes and spring-shock combinations.”

However, a factory crossmember in good condition may be able to do the job, according to Bicknell.

“The OEM crossmember with the correct components has been, and can be, a very formidable component when set up properly,” he said.

What’s important, added Brown, is that the frame is stiff enough so it doesn’t act as fifth and unwanted suspension member. Heidts offers structural upgrades primarily for classic Camaros, Novas and Mustangs.

“The Camaro and Nova had bolt-on front subframes, so we make bolt-on replacements from 2- x 3-inch tubing, for the first- and second-generation Camaro, and for the first generation Nova” said Heidts engineer Owen Bassett.

On these same GM cars, “the rear frame rails are part of the body tub, so Heidts also offers frame connectors to link the front subframe to the forward attachment point of the rear leaf springs—essentially giving a Camaro or Nova a complete 'frame' from bumper to bumper," according to Bassett.

The Ford Mustang, on the other hand, was a true unit-body, with integral frame rails reaching forward from the front of the floor pan and rearward from under the rear seat.

“We make frame connectors to connect those pieces—and that will make a Mustang more rigid,” said Bassett, who added that Heidts will soon release a more radical kit for the early Mustang that will require cutting the original shock towers and welding in an all-new double crossmember with a contemporary suspension.

"We’re going back and revising all of our installation instructions [for all of Heidts' frame products]," Brown said. "Based on the feedback we’ve received, we’re trying to make things easier for the installer.”

Scott’s Hot Rod Shop also offers a complete front subframe that replaces the forward monocoque on a 1962–1967 Chevy II/Nova, plus a rear subframe and frame connectors that essentially convert an early Chevy II to a full-frame car.

“We just finished one for a customer who has an honest 720 horsepower,” said Padfield, who added that Scott’s also offers frame kits for cars dating back as far as the 1926–1927 Ford.

“If a customer wants, say, a 1965 Mustang to handle like a newer car, then there are a couple of things we can do,” he said. “Usually we build a front suspension that used the stock unit-body.” 

Fully Framed

Scott’s also builds high-performance full-length custom frames for cars that came with full-length frames from the factory, such as the 1965 Chevelle.

“The Chevelle frame was a poor design right from the factory, and this one had been goggled-up over the years by the who-knows-how-many hands it had passed through,” said Padfield.

This particular customer had some very specific ideas, which helped guide the design of the new frame. These specifications included a 900-horsepower engine, air suspension with a 4-inch ride height, 14-inch disc brakes at all four corners, and 9- x 18-inch wheels in front with 12- x 18-inch wheels in the rear.

“In the factory design, the frame actually sat under the rocker panels, so you could see the frame in the side profile,” said Padfield. “But this customer wanted a very low ride height, so we cut the floor pan out of the car and channeled the body over the frame rails so the floor was now flush with the bottom of the frame. That allows us to get that very nice, aggressive ride height, without any exposed edges of the frame being visible in the side-view profile. We also incorporated a tubular X-member. That adds a tremendous amount of strength to the chassis foundation.”

We’ve heard of even more radical surgeries, where full-length frames were installed under original unit-bodies, but VanDervort advised extreme caution whenever a frame conversion requires cutting the original body.

“Where do you put the frame rails?” he asked. “You can take 2 or 3 inches out of the footwells, but then where do you put your feet?"

“Or you can make it so it goes underneath the rockers, with no modifications to the body, but then it hangs underneath there and looks [ugly], so that’s not the way to go, either,” VanDervort added.

This is why subframe connectors of the kind that Brown and Bassett of Heidts described are so popular.

Gregson confirmed that adding a full-length frame to any unit-body car is not an option without major modifications.

"However, running a set of reinforcements or subframe connectors effectively marries the front subframe to the rear frame, strengthening the chassis for better overall handling and allowing it to deal with a higher level of horsepower,” he said.

3-D Visions

While allowing that it was probably “overkill” for a street car, VanDervort offered an alternative idea.

“If I were going to build a car like that  with front and rear subframes, instead of trying to beef it up from underneath, I’d give it some altitude with a cage,” he said. “Then you have a supported truss and not just a ladder frame."

“With any single-plane ladder frame, you’re limited by how much depth you can build into it," VanDervort continued. "They don’t build bridges that way, they build bridges with an arch over the top, so once you’re talking about more horsepower or cornering power than a unit-body can handle, you really should be talking about a roll cage—not only for safety, but also to save weight. If you’re building horsepower, weight is your number-one enemy. And you can get more strength out of 100 pounds of cage than you can out of 200 pounds of frame.”

VanDervort  recommended RideTech’s Tiger Cage line to do the job.

“Any time you are building a serious performance-oriented car, you want to seriously consider body stiffness,” said Bicknell of RideTech. “There is a myriad of aftermarket components that address this issue, from subframe connectors to our bolt-in Tiger Cage—and the great majority help one way or another.”

“A roll cage is a customer choice based on use,” said Brown. “The more cage you put inside a car, the more rigid the platform becomes—but it also starts to become restrictive.”

He agreed that a cage may be appropriate for racing but is probably unnecessary on any street-driven car. Padfield suggested testing the customer’s tolerance for horsepower before even thinking about the frame.

“A lot of customers come in and say, ‘I want 1,200 horsepower,’ and the question we always ask is, ‘Have you ever been in a car with that much horsepower?’” he said. “A few years back we built a car that has an honest 1,200 horsepower at the flywheel, and, on a chassis dyno, an honest 960 at the rear wheels. We built it for a drag racer who knew exactly what he was getting into.”

Padfield said that sometimes Scott's Hot Rod Shop will call on this individual to give these horsepower-hungry new customers a ride in his car so they can get an idea of what 1,200 horsepower actually feels like.

"And they come back to our shop and say, ‘I don’t need that much horsepower," he said. "They had no idea what 1,200 horsepower really felt like.”

Fins ‘n’ Frames

In any case, while other manufacturers emphasize muscle and pony cars, Fatman Fabrications is focusing increasingly on cars from the 1950s. Fatman debuted a complete rolling chassis for the 1949–1951 Ford at the 2011 Hotrod & Restoration Trade Show

The company didn't  design  the  chassis because of any particular problems with the car, VanDervort explained, “but because people were starting to build more of them, and investing enough in them that it justified a new frame, and that justified our investment.”

The frame rails on the Fatman chassis are 4-inch square, .188-wall tubing, with an added X-member.

“It’s patterned after the 1955–1957 Chevy frame that’s been very successful for us," VanDervort said. "Both original frames were open, but boxing the C-channel, adding that fourth side makes a big difference in strength.”

Reproduction frames for other popular collector and/or muscle cars are also available. But once you step outside that relatively narrow range of popular vehicles, the issue becomes more difficult. 

“We’re making a one-off reproduction frame for a 1934 Dodge right now because nobody else does,” said VanDervort. “Most of what’s available is for Ford and Chevy, and even that goes by supply and demand. No one offers a frame for a 1948 Chevy, for example, because they don’t seem to rust out, and because it’s usually not a first-choice car for a high-end build.”

Fatman does offer over 160 front stub frames for 1964 and earlier cars.

“We think that 1950s Buicks, Pontiacs, Cadillacs and Oldsmobiles are going to be the next big thing,” VanDervort continued. “There are a lot of those cars out there and people seem to really like them. You can build a 1962 Buick bubble top instead of a 1962 Chevy bubble top, and I think we’re going to see a lot more of that.”

One reason that hasn’t happened is that a lot of those cars have a front suspension that’s particularly difficult to work with, VanDervort said. 

That’s why he believes it’s easier to saw off the frame at that firewall and weld in one of Fatman’s vehicle-specific stubs.

“It’s pre-fitted with bumper and radiator mounts, so in one day you have modern suspension, steering and brakes on [any of a wide range of makes]," he said. “We tell people that if they already have a restored car that already has the brakes and front end rebuilt and the original engine, and they just want to set it down lower, then a set of drop spindles are a great way to go. But if you’re building a barn car, you are going to be further ahead just cutting all that stuff off, then put in modern brakes, a power rack and a front end that anyone will understand how to align.”

It all fits with VanDervort’s vision of making chassis work easier for the do-it-yourself builder.

Referring again to his 1949–1951 Ford chassis, VanDervort said that “the kind of customer who is building that car doesn’t want to be on his or her back for a month on a creeper," he said. "Age creeps up on us, and the less time we spend on a creeper, the better off we are. When you get into your 50s and 60s and beyond, an hour on the creeper means four hours of rehabilitation. It’s a big part of it.”