(originally posted 1/19/2012. Updated 12/21/2022 with information from “The Cadillac Frame – A New design Concept For Lower Cars” a paper submitted to the SAE by GM engineers that was provided to me by George Ferencz)
GM’s X-Frame, upon which millions of GM full-size cars sat from the years 1957 through 1964 (Buick Riviera through 1970), has generated plenty of controversy, speculation, and accusations. Since there seems to be no complete survey of the X-Frame—at least any available on the web—let’s lift off all those handsome and finned GM bodies by Fisher, and take a closer look at what’s really under there.
Starting with a real stunner: The X-Frame first appeared in 1957, underpinning the new C-Body Cadillacs and Eldorado Brougham (pictured). It was conceived as a way to facilitate lowering the total vehicle height yet still allowing for reasonable leg room via deep floor wells for the passengers’ feet to drop essentially to the bottom of the car, unimpeded by frame rails. This was not possible with the ladder frames then in almost universal use, except unibodies, of course.
Placing ever-lower bodies on ladder frames created serious negative impacts in interior space efficiency, as Chrysler found out with its Forward-Look 1957 models. Both leg and head room were limited, and the seating position was close to the (high) floor. The solution at Chrysler was to convert their cars to unibodies in 1960, resulting in improved interior metrics, as shown in this comparison graphic. GM considered unibodies, and would use them on their compacts starting in 1960, but dismissed using them on their large cars for a number of reasons, of them being that it would be much more difficult to offer a wide variety of body lengths and styles. For instance, engineering unibodies for the extended length Cadillac 75 limo and commercial chassis would have been very expensive and difficult. Also, it was much easier to “tune” a frame to the corresponding body to minimize noise and maximize comfort. This undoubtedly explains (at least in part) why Chrysler continued with the full frame under the Imperial through 1966.
The 1957 Cadillac Eldorado Brougham was only 55.5″ high, and the other ’57 Cadillacs were also going to be lower than their predecessors, so the Cadillac engineers needed a new solution in regards to the body and frame. The existing ladder-type frame was simply not going to work. The height of ladder frames had already been reduced a few years earlier to allow lower bodies, by utilizing box sections and other stiffeners, but there was no further reduction possible.
Cadillac did build an experimental car in 1950 with something akin to the perimeter frame that would eventually supersede and replace the X-frame, but torsional rigidity was severely compromised. Adding X-members to the frame created the desired rigidity, but then there was the problem with intrusion into the leg room area.
The X-Frame was the result of a number of years of experiments between Cadillac engineers and A. O. Smith Corp., who actually built all of GM’s frames. It combines aspects of two very distinctive frame designs: the backbone frame and the X-braced ladder frame.
The backbone frame originates the 1908 Rover 8 h.p., which used a rigid steel tube as its primary member. Since it had a rigid rear axle, the suspension at the rear was by mounting the body on semi-elliptic springs.
Hans Ledwinka’s revolutionary Tatra T-11 of 1921 (full story here) took the central tube chassis and made it more effective by adding independent rear suspension via swing axles. The strong solid steel tube was the carrying member for the whole car and its (lightweight) body.
The Tatra tube frame evolved into a combination central backbone-platform frame, as seen here in the mid-thirties Tatra 97. Needless to say, a very similar route was also taken by others, including Porsche for the now very-familiar (and similar) VW platform frame. In these, the body was rigidly bolted to the platform, to create essentially a unitized structure from the two halves.
The pure backbone chassis was taken up by others, none more famously so than by Colin Chapman, with his brilliant Lotus Elan. With a very deep central section, which did not create problematic interior intrusion in a sports car, the Elan had unparalleled rigidity, the ultimate goal of any frame/body structure. Rigidity is the only way that a suspension system can be designed to optimize its function.
On the other end of the spectrum sits the ladder frame, here immortalized in the frame rails from a Ford Model T. A certain amount of flex was an intrinsic part of the equation. Its origins are obviously in the heavy timber frames underpinning wagons, but the seminal 1901 Mercedes was perhaps the first to sport something akin to what became this timeless approach to automotive frame building
Jumping ahead about a century, here is a modern ladder frame, as now used in pickups and BOF SUVs. Note: this is quite different than a perimeter frame as used in most American passenger cars. The ladder frame is still very much under the body, and provides almost all of the overall rigidity, unlike a perimeter frame.
The origins of using an X-member to reinforce a ladder-type frame has been credited to the fwd Cord L-29, and this excerpt from its brochure substantiates that claim.
But this 1939 Buick frame shows that its adoption had expanded by then, and for obvious reasons. It undoubtedly increased rigidity, at least in certain planes.
X frame centers were also widely used to stiffen ladder frames as needed, specifically for convertible or commercial car use. This is a sedan frame for a ’57 Chevy.
And here is the center section for the convertible version. It’s important to note that the bodies of BOF (body on frame) cars contribute to varying degrees to the overall vehicle rigidity, which is why convertibles require additional reinforcement to their frames.
The X-Frame that GM came up with involved a very strong center backbone section, which could be built in different lengths to accommodate varying wheelbase lengths. Converible and extended wheelbase frames used thicker steel in the center section as well as some other reinforcements. The 1957 convertible frame weighed somewhat less than the 1956 convertible frame, but had roughly equal torsional rigidity and 100% improved maximum beaming deflection. The non-convertible frames had improved torsional rigidity.
This ’61 Chevy X-frame shows the details of its design and construction. It did result in a somewhat larger central tunnel in the interior, a distinctive feature of all X frame cars and a trade-off for the deep foot wells on either side. Obviously those confined to sit in the center of the seat did not see any advantage.
In order to make the X-Frame work, Fisher Body increased the strength of the rocker sills of the bodies, as well as side-to-side stiffeners in the floor. These can be seen fairly well in this shot of a ’58 Chevy. In essence, GM was transferring a substantial amount of the overall structure’s strength to the body; certainly any side impact resistance that this intrinsically vulnerable design might have had. The issue is not only whether the body sills had enough strength for that purpose in the first place, but these rocker sills were notorious for collecting moisture and rusting prematurely.
But before we discuss the X-Frame’s safety weaknesses, real or perceived, let’s do a survey of what all the GM divisions were doing frame-wise during this period. Contrary to some assumptions, not all the divisions used the X frame, either at all, or at least not during some of the time.
Vehicle design and construction at GM then was almost the exact opposite of today. Now, numerous vehicles (and brands) with distinctly different bodies share a “platform”, generally the key underbody structure, suspension and/or floor platform. Back then, Fisher body engineered a common body to be used by various divisions, but each division engineered its own vehicle otherwise, including the frame, suspension, drive train, etc. It really was ass-backwards; or it certainly came to be so, given how increasingly little folks actually appreciated what went on under the floor, at least very technically speaking. And it was inevitable that GM would eventually centralize these aspects.
But this was not the case during the X-Frame’s reign. The ’57 and ’58 Buicks, which shared Cadillac’s big C-bodies, did not go with the X-Frame, keeping an X-strengthened ladder frame.
The result was…a high rear floor, right up to the bottom of the cushion. Of course the center tunnel was quite modest.
As a point of comparison, this picture of a ’58 Cadillac rear seat clearly shows the lower floor but larger center tunnel.
Rather curiously, for 1959 Buick even dropped the X center-reinforcement, going with a modified semi-perimeter frame, with a K-type front section. It looks very similar to Ford’s “cow belly” frame, in that it did offer room for rear seat foot wells, but not for the front seat area, as the frame narrowed down there.
But beginning in 1961, Buick fell in with the X crowd, even touting it as the “Safety-X-Frame”. Full-sized Buicks stayed with the X Frame through 1964.
The Riviera maintained its X-Frame all the way through the 1970 MY. Here’s a 1969 Riviera showing off its skeleton. And for those that live with the false assumption that X Frame cars were intrinsically poor handlers, the Riviera in GS guise was generally highly regarded as one of the most capable handlers in its size class. Even the base Riviera was considered to be quite good in this regard.
The X-Frame was plenty stiff, and the handling of the cars that used it was not due to anything about the frame, but was a matter of suspension geometry and tuning.
Olds was the only member of the GM family to not use the X-Frame at all. The ’57-’58 Olds frame looks quite similar to the same vintage Buick frame.
But for 1959, Olds came up with what is essentially a variation of the X-frame, incorporating wide side rails to do the work that the reinforced body sills were asked to do on the true X-frame cars. These side frame rails (or similar) have been widely adapted to high-performance X-frame cars, creating an overall stronger, more rigid frame. And that came without any sacrifice in the X-frame’s deep floor wells. Call it the improved X-Frame.
The other unique aspect about the ’57 – ’60 Olds chassis is that it had leaf springs in the rear suspension, the only GM full-sized rwd cars to do so during the whole modern era, except for the ’71 – ’76 “clamshell” wagons, which did so for space reasons. The ’57 Cadillac used leaf springs too.
For 1961 through 1964, Oldsmobile used a perimeter ladder frame. Note how much emphasis Olds places on the safety of “Steel Protection All Around”.
The frame Olds used those years (’63 in drawing above)…
very much predicts the frame all the GM full-sized cars went to in 1965 (Riviera excepted). This one is from a ’69 Cadillac. Olds’ reputation for engineering advancements among the GM divisions seems to have gone all the way down to frame design.
Interestingly, Pontiac did not show off its frames in its brochures, unlike the rest of the divisions. John DeLorean, who was then running Pontiac, was an engineer by training, but was also an excellent marketer. He thought GM was generally lacking in modern marketing techniques at the time, and perhaps that explains why Pontiac frames didn’t make it into brochures. Who cared? Folks were much more interested in how they looked, and even how they drove. Pontiac accentuated its very visible Wide Track stance, and left folks guessing about the frames.
But as the above frame spec chart shows, Pontiac followed Chevrolet and Cadillac with X frames for ’58 – ’60, but then went to a perimeter frame for ’61 – ’64 that looks very similar to the ’61 – ’64 Olds frame. (Canadian Pontiacs, essentially Chevrolets under the skin, did keep the X frame for ’61 – ’64)
Chevrolet’s “little brother” relationship to Cadillac was more than skin deep, inasmuch as the two of them were the most consistent users of the X-frame; from ’58 through the ’64 MY, in Chevrolet’s case. Here’s the ’59 version in full display. The ’58 was unique to that MY; the ’59 – ’60 frames were identical, as were the ’61 – ’64 frames.
The ’59 Chevy became famous in 2009 when it was crashed into a new Malibu, and (not surprisingly) fared rather poorly. The X frame played little or no part in that, given all the other aspects that were so different between these cars.
The X-frame is somehwat notorious for rusting, and there is a pretty brisk business in replacement frames, often reinforced. One wouldn’t want to start throwing a Chevy low-rider hydraulically four feet into the air with a rusty frame.
In Ralph Nader’s “Unsafe At Any Speed”, the X-Frame merits some less-than flattering attention. Here’s some excerpts from that:
A case in point is the “X” or “cruciform” type chassis frame. This frame was introduced in 1957, primarily to reduce the problem of restricted headroom and difficult entry into the “low-profile” automobiles that were becoming popular after the mid-fifties. The X frame construction does not have side rails along the passenger compartment, as did most previous conventional frame designs. From the time the cruciform type frame was introduced, it was widely used by General Motors on Chevrolet, Buick, and Cadillac. The Ford Motor Company continued to use frames with side rails, and it was evident that the two companies held strongly different opinions about the two designs.
In the fall of 1959, a photograph of a Chevrolet Impala that was broken in half after striking a tree broadside was widely circulated in newspapers throughout the country. The frame had severed at the intersection of the X. The report of the General Motors investigators who rushed to the scene attributed the severance of the frame to the semi-airborne position of the car as it struck the tree. This had apparently allowed the engine mass to act as the head of a sledge hammer. At the General Motors engineering center in Michigan the conclusion was that “automobiles are not designed to withstand such tremendous lateral forces – this would be extremely uneconomical.”
General Motors spokesmen continued to defend the cruciform type frame as offering substantial resistance to side impacts because of the rocker panel and floor pan underbracing members — even though by 1965 all General Motors models except the Buick Riviera had abandoned the design in favor of the perimeter type. In 1960 the General Motors technical center offered proof that a unitized structure with side rails can also split into two pieces. A picture of a Ford Thunderbird, torn in half after slamming against a telephone pole and tree, was offered as evidence to critics of the X type frame.
This comparison enraged Ford engineers. Fletcher N. Platt, a highly talented research engineer at Ford, retorted that the Thunderbird case involved a telephone guy-wire that had “acted as a knife on the entire body structure.” In contrast, he said, “the Chevrolet that broke in half failed at the center of the X frame after hitting a tree.” Platt said, “The X frame has no advantages from the standpoint of passenger protection. It requires less material to support the four comers of the car, but it is obviously less rigid and provides little lateral [side] protection to the passenger compartment.” He suggests consulting any “‘unbiased’ structural engineer regarding these two designs.” Mr. Platt might not consider Mr. Harry Barr, vice president for engineering of General Motors, qualified for the designation ‘unbiased,’ but Mr. Barr did admit grudgingly, under questioning, that the Oldsmobile perimeter type frame had some advantages over the Chevrolet X type frame in side-impact crashes at speeds of about fifteen miles per hour. Further proof that some General Motors engineers agreed with Ford’s Platt came in the form of an internal memorandum prepared by the Oldsmobile division in 1963 in which the Oldsmobile “guard-beam” frame was described as offering an “extra margin of protection” over the X type frames of Chevrolet, Buick, and Cadillac.
I was unable to find the picture of the broken-in-half ’59 Chevy cited here. Undoubtedly, a side impact, especially against something like a tree or pole, would be the X-frame’s most vulnerable aspect. There are other anecdotal negatives commonly cited on forums, such as cracking of the rear body sills, as well as other minor structural infirmities, especially with advanced age. The two-piece drive-shaft used with the X frame also comes for a lot of hate, especially the weakness of the center bearing, and the joys of replacing it.
But Ford clearly saw a marketing benefit to the X-Frame controversy, and touted their wide perimeter frame as a safety advantage over the X-Frame in their marketing materials, as in this on from 1960.
On the other hand, when a car T-bones another, the bumper and front body mass is almost invariably above the height of the frame side rails, so the resistance to impact is mostly in the body structure itself. It’s hard to make a very compelling argument against the safety of the X-Frame, considering that unibodies obviously don’t have frame side rails either. Passive safety is the result of numerous improvements that have taken place since then, and obviously modern car bodies are vastly stronger and safer.
Our exhaustive look at the X Frame is complete. If you made it this far, you’re now something of an expert. Hopefully, others will add further facts or insights.
Related CC reading:
Tech History: The Perimeter Frame – Body-And-Frame, Not Body-On-Frame
I’m wondering what the “magic bullet” is that allowed something relatively small, like that Civic, to sustain so little damage while utterly demolishing something larger and heavier like that 442. Is it the high strength steel? Is it the rigorous structural analysis allowed by CAD? Is it a “safety trumps all else” mentality when designing a new car? Or maybe there Is no magic bullet and it’s the cumulative effect of all these advances.
It also makes me wonder about the modern era safety of some cars that were considered paragons of safety in their era, like a W126 S-class or a Volvo 240. Still relatively safe, or does the simple fact that they are mild steel rather than high-strength consign them to the “death trap” category compared to most anything they might be unlucky enough to be involved in an accident with? I used to think that a logical next move from my current Crown Vic could be something like a Volvo 960 or v90 wagon, in that it’s old enough to be inexpensive, but was considered a safe car in its day. Maybe that’s a fool’s errand and even the thought of using something like that as occasional family transport is a sign of a mental deficiency.
I’m wondering what the “magic bullet” is that allowed something relatively small, like that Civic, to sustain so little damage while utterly demolishing something larger and heavier like that 442.
Decades of continual improvements. Sophisticated computer analysis, better materials and the accumulated know-how that can make even a Smart do quite well in head-on crashes against big and heavy cars.
You might want to do some research on your second question. Generally, the newer the design, the safer. Of course, some car/manufacturers were always a bit ahead of the mean at any time.
multiple things:
Modern car: front “subframe” and structure ahead of the firewall is designed to “crumple” in a controlled manner. This both dissipates energy via heat (bending metal rapidly makes it very hot) and reduces the acceleration the occupants feel by spreading the crash “impulse” over a longer period of time.
Old car: Who knows? The front frame horns could just buckle, or punch right into the opposing vehicle. This stuff wasn’t really tested back then.
Modern car: The passenger cage is designed to be as rigid as possible, so once the crumple zones have been, er, crumpled, the colliding vehicle should stop hard at the A-pillar/front of the door aperture. On some modern cars, the driver’s door could still be opened after an offset-frontal crash.
Old car: the passenger cage wasn’t very rigid, so once the colliding vehicle reached the A-pillar/door it just kept crushing the body structure. Note that the instrument panel bolts to the front of the passenger cage, so once that is compromised the driver was about to get a faceful of steering wheel.
Modern car: The power pack (engine/trans) is designed to drop down some and “submarine” under the floorpan to some extent.
Old car: The engine/trans just got pushed back, crushing the firewall and leading edge of the floorpan, which would break the front seat occupants’ legs and push the IP even harder into them.
Modern car: Seats remain firmly bolted to the structure, at least in a collision of any reasonably survivable severity.
Old car: not uncommon for the seat(s) to be torn free from their mounting points, especially if the floorpan is being deformed by the crash.
Modern car: Front and side airbags try to prevent the occupants’ heads from striking any hard surfaces, reducing head, neck, and spinal injuries.
Old car: hope you like your new wheelchair.
The Volvo 940 is “famous” for been demolished in a head on crash with a little Renault Modus here in Europa.
That beeing said, an american BOF, like the GM 77-91 B/C-body will demolish any Volvo 240/740/940 in an head on crash. I have even seen an 78 A-body total a 240 in a head on collision many years ago.
That beeing said, an american BOF, like the GM 77-91 B/C-body will demolish any Volvo 240/740/940 in an head on crash
First of all, the 740 and 940 are totally different cars than the 240. And second, I wouldn’t make assertions like that unless you can back them up. And any one crash isn’t going to tell the full story either; there’s lots of variables. This isn’t like rooting for your favorite football team to demolish another one.
Well, these old style BOF construction are very very rigid, not saying that’s a good thing in a collision, the point with the new cars is to absorb the forces, an old style american BOF don’t do so much of absorbing, and for it’s time it was regarded as a safe car. For many years in the 80s I remember the Caprice, or other B/C -bodies were the cars (on the statistics) with the least personal injury after a crash.
I’ve seen a Volvo 240 and a Malibu after a crash, the Volvo was totaled, the Malibu was able to drive from it. The 240 was around 1982 (it was Norways best selling car for years and they were everywhere…) and the Malibu an 80 model Wagon. Some years later I saw a 87 Volvo 740 who had run into a 81-82 Caprice (might have been a LeSabre, but a B-body), same story there, but bigger damage to the Volvo.
Like you wrote, there’s a lot of variables, but these collision was about head on, and at relatively low speed.
“Well, these old style BOF construction are very very rigid,”
you cannot say that with any certainty. just because the architecture didn’t have any “crumple zones” doesn’t mean it’s absolutely rigid. A straight frame rail can easily buckle in a collision.
“I’ve seen a Volvo 240 and a Malibu after a crash, the Volvo was totaled, the Malibu was able to drive from it.”
yes, and I’ve seen a Dodge Ram pickup rear-end a Honda Civic, and the Ram was the one totaled. why? because the driver of the Ram braked hard and late, and his truck’s bumper went under the Civic’s.
Also worth noting that the relative amount of damage sustained by a given car doesn’t necessarily mean it’s safer. Often times a car with a properly designed crumple zone will “look” more damaged after a crash, and will in fact be totaled, but the passenger cabin will still be intact and the occupants spared serious injury. This, opposed to a car that “looks” like it took less damage, and might even be driveable, but in which the passenger cabin has been compromised.
The video, on the other hand, is fairly damning. That 940 driver would be all kinds of dead, whereas the driver of the Modus would probably not have been injured.
These rigid(yes they are compared to other cars) BOF cars didn’t have very much crumple zones, a very short one is designed behined the bumper on 73 and newer cars. But the BOF cars will use the other cars crumple zones, and with its frame and weight it will fare ok compared with old school unibodies who collapses entirely (often) in a crash with a modern car.
The safest car is a new, big and heavy car who it not a SUV. If you want to drive an old car and safety is an issue, the oldschool BOF cars with it’s frame and weight is the safest of the old cars, for the most type of a crash, but again, there are a lot of variables.
In the video the Volvo is not very much heavyer than the Modus, and the new car demolish the old unibody Volvo. If the Volvo where a 1975 Lincoln Town car of 2,5 tons BOF construction the car would have been better of, but the passangers? I don’t know.
Keep in mind the seatbelts too. We had an 80 cutlass growing up and I always felt that the rear lap belts would allow my back to bend in half in an accident. I didn’t understand how it could be safe but I was a kid and didn’t question it. In ’88 we got a Volvo 740 and it had rear shoulder belts. I would much rather be in an accident in the Volvo than the cutlass!
Hi, first post. I just found the site and have had a great time reading recent articles and comments and so have decided to wade in on the shallow end. Please forgive my tendency to ramble. :^)
I owned a 240 wagon for a while. Bought with a lot of miles but a service history, typical of cars I buy. It was easy enough to work on, and good thing, it needed attention periodically. Some of the repair bills in the service history were astounding. Another 240 owner described it as understanding the difference between reliable and durable. I did all my own work with the exception of pressing the rear suspension bushings, so I got to know it well.
So I visited various parts yards regularly. On a particular sunny summer day this yielded an unexpected benefit: I visited a yard where a man was working with a lift, moving carcasses around. He stopped and watched as I began picking for whatever it was I needed that day.
As I walked around through the tall grass between cars, I saw some Japanese makes sitting there, some looked like they had come through their accidents with much more aplomb than some of the Volvos, which were pretty smashed.
The man got off the lift while I was examining a particularly nasty 700/900-series Volvo hulk and shaking my head. I turned to him and asked, if Volvo’s are so tough, why do they look like this after an accident?
So he opened the door of the Volvo (yep, it worked, would not have even tried it from appearances), we looked at the footwell. He pointed out how it was largely intact and in normal shape. We went over to one of the Japanese ones, the body looked better, almost like it would be worth fixing, but he pointed out a large intrusion into the front of the footwell, it had collapsed upward and inward pretty far, enough make me shudder a little. The door on that car was sprung and didn’t move far.
We agreed that the accidents probably weren’t the same, but he said in general the safe Euro makes had the best steel and passenger compartment integrity. We walked around and looked at examples of various brands and this held up, despite what the external appearance was.
He told me that Volvo, Saab, Mercedes, BMW, and Audi were the hardest to scrap, he hated cutting them up. While walking around we found a Volvo with its roof cut off and he showed me how the A-pillar was composed of intertwined folds of thick steel. Not much room left for air in that pillar. I realised why my wagon felt like such a heavy solid chunk.
So I looked around, still processing his info, and saw an Audi with its roof severely caved in. I asked why they were so vulnerable up top. He told me the wreck story of that car: It had slid on wet pavement, caught a wheel and ended up on its side on a railroad crossing. The roof had been hit by a train. The driver survived. At the time I was a locomotive engineer, it did look like a coupler had hit the roof. I nodded and thanked him for taking time. They didn’t have the parts I wanted, but I got something even better.
I had just sold a Camry wagon, which was more modern and smooth than the 240. Now I had some food for thought about why selling it might have actually been a good move, beyond indulging my mechanical curiosity about Volvos and wanting a 5-speed.
One new ritual about owning a 240 was meeting other owners. I’d come out of a shopping center and find other Volvos parked around mine. People would come up to me and tell me stories about how their 240 died to save their family’s lives. (One man spun on ice and and hit a bridge abutment backward at 70 and the worst that happened was spilled coffee. He and his family walked away, none of them harmed.) Some would be moved to make an offer, saying that they missed their 240, and they were driving newer models that I envied. They’d forgotten how the driver’s window stopped working at a tollbooth, or how it wouldn’t start on a rainy day. :^)
It was like being a member of a cult. It was probably also a little cheaper than Scientology… if I got my parts used. :^)
Just kidding IPD, I loved you guys!
Nice t’meet you all. Keep up the good work.
You are indeed correct about 240’s. The statements prior to yours about 240’s not being drivable after an accident compared to other vehicles do not tell the whole story. 240’s all had front and real crumple zones, also the engine was designed to be pushed under the firewall in the event of a frontal collision. Side impact door bars, 4 wheel disc brakes, 3 point seat belts, collapsible steering columns, split system brakes allowed braking in the event of any major failure (hard to explain). So yes, the 240 wasn’t drivable… Exactly, it is made to absorb the impact instead of the passengers. They were great cars. Many irritating things like the whole car being built around the blower motor, crummy ceramic Euro fuses (which are the cause of most failures) Flame trap PVC type system, being the ones that stand out. However, once you get these worked out, one will have many, many miles of dependable service. But, IF you don’t, or can’t do your own work, they will cost you a fortune
I’m all for making cars as safe as possible, but the driver is still the most important factor in avoiding automotive deaths. However, you probably should research whatever you buy, even if it’s from safety icons like Volvo and MB. I can still remember the time Volvo was caught flat footed when their 1980 240-series sedan failed the federal 35 MPH crash test quite badly, while the $3,500 Chevette did quite well. Apparently, Volvo allowed to much slack to build up in their shoulder straps to keep the driver away fro the wheel, while the Chevette’s torturously reclined driving position gave the belts plenty of chance to cushion the blow.
I`m not an expert,but it looks like the X Frame chassis needed more structural interity in the middle ,where the frame was it its narrowest part, but obviously this was a sucessful design because it served GM for many years.
Back in the 1970s, when he was his 20s, my boss at work was seriously injured when he got t-boned in an x frame Chevy. Got pinned between rocker panel and trans tunnel. Spent months in the hospital in traction. He is 60 now,and still feels the effect of it.
I find it amazing that GM Corporate allowed each division to design, develop and produce such an singularly important component as a body frame; being that it was essentially identically-sized variation of sameness that few customers would ever gain an appreciation for. That Fisher Body, a mandated and common resource for all divisions determined the more cosmetically and tangible body hardpoints (with the very visual consequences following on from that) but not the underlying frame as well seems to me to be an artifact left over from the days before the GM brands were collected together. It just seems to be such an obvious area for economy that GM accountants would have quickly zero-ed in on it well before the ’70s. I can understand each division wanting to maintain control over their engines and styling distinctions, but it really surprises me that something as baseline as a car’s frame would retain such a byzantine level of complexity for so long. I guess it also explains why GM held-off going to corporate-wide use of the modern monocoque/unibody for as long as they did poor things. What a waste.
when you own over half of the market, you can justify a lot of different things.
In retrospect, it was a strange state of affairs, especially for the company that essentially invented the annual styling change and focused so much on style to sell cars.
But it was mostly the product of tradition: automakers traditionally quite often didn’t make their own bodies at all, and if they did, it was from a separate operation. They were mostly in the business of building and assembling a chassis; that was the “real car” part of their operation.
Which is of course why the carmakers bought all those body suppliers, like Fisher. But they continued to design and build their own chassis, like they always had.
In retrospect (and I hinted at it in the post) it would have made more sense to standardize the chassis and spend more money on differentiating the bodies. But keep in mind that the bodies quite often really were changed extensively every year or two or so, which was a massive investment. That was a much bigger investment than having each division build their own frames.
Obviously, this all needed to change, and it did, starting in 1964 and 1965, when the A and B-C bodies all got common frames and suspensions.
“Obviously, this all needed to change, and it did…”
My opinion is it changed only because of increased competition.
The whole idea of changing everything every year across all branches of GM and doing so semi-independently of eachother worked well for GM. For awhile. It was probably the most impressive thing GM ever accomplished. It was probably the most powerful marketing ploy ever devised. It was probably the single greatest force in creating the world famous American car culture.
I am not a chevy fan. But I recognize the amazing thing GM accomplished in this time period.
Back to the topic of this thread…the X frame is one of the stupidest things GM ever did in my opinion. I say that with hindsight however. In the heat of the moment, for a temporary solution, maybe it was genius. I don’t know. After all, when it comes right down to it, in the grand scheme of things…every solution is a temporary solution.
Fascinating! If I ever buy a ’58 – 60 GM car, think it will be an Oldsmobile. Despite the Ford’s perimeter frame having better side impact protection, it would be interesting to see how unitized cars such as a 1958 – 60 Lincolns fared in the same side crash tests with a tree. For that matter, Chrysler’s later use of unitized construction from 1967 on. Were these more vulnerable than ladder frames from GM?Or were they reinforced sufficiently for a side impact? Just wondering. . .
I was wondering the same thing about Chrysler’s unit construction.
When looking underneath them, the main structures connecting the front and rear sections together, aside from the floor pan itself, are the door sills, which must have been super strong.
I haven’t looked under a convertible but I suspect they look the same ?
Many early unibody structures put most of their strength in the sills — the MGB and early unitized Jaguars are good examples. It tends to give you sills the size of an Alp, but it does make it easier to create convertibles (or custom bodywork) and helps keep the CG low, I suppose.
Those are not early examples, early would be the Morris Minor or 38/9 Vauxhall 10/12 or even a Velox or a Mk1 Ford Zephyr ans convertibles were created from all those.
I would think the convertible would have to have some kind of additional support. The long time Mopar afficionados here will probably know . . .
After reading this article and studying all the different kinds of frames that the Big Three have utilized, it leaves me imagining solutions to the side impact problem. It’s one thing for a car’s structure to succeed at surviving numerous low speed hits, as in a demolition derby, (Imperials and ’71-’76 GMs as everyone has already discussed), but even these cars don’t have the bracing for a side impact where the B-pillar and mid-section doesn’t bend in a strong, higher speed impact with a tree or a phone pole. Consider the possibilities with the advances of today’s technology. Why not extend the safety cage concept as it is now, to also have a central roll bar that is not only run through the ceiling, but also x-braced through the middle? Think of the lines of a Union Jack flag, but without the central vertical line (horizontal line through mid section would stay). Provided the front seats don’t get shoved into this frame structure during an accident and impale the occupants, and that is trusting someone’s earlier observation that modern day car seats are sufficiently mounted to the floor so as not to come loose – such a frame would at least provide a strong area around the center of the car that would keep the sides from caving in or wrapping around things so easily. In addition, up inside the roof, out of view, could be another frame of this same design, where the legs of the X come to the frame at the A and C pillars; this would meet up in the middle with the structure in the center to create a very strong roof, albeit perhaps making the car taller. The whole energy absorbing concept would go to hell with this scenario without adding additional side crumple zones beyond this Union Jack frame that would either make the car too wide (over 80 inches) or sacrifice shoulder and hip room to a degree. But in a modern vehicle with proportions similar to an Imperial LeBaron or Lincoln Town Car of the early 60’s, it would be interesting. One would imagine that fuel economy might not be so great in a car with all this bracing, though. Perhaps as good as a sherman tank :-p
WoodGrain… I think you answered your own question in part with your closing statement. Weight, Construction Costs, and Fuel Economy. The idea these days is trying to be light and strong. Another problem with adding a X with today’s designs is that there really is no way to do it with a unibody built car. The X was basically eliminated because of floor (leg room) clearance and lowering body profile that also improves center of gravity. A couple of convertibles such as C4 Corvette and the 2000-2005 Thunderbird, used X straps to help with sag and twist but they were not used for impact safety.
1990 Corvette Convertible seen below.
Paul, it’s interesting to see what the patent document (filed 1956, approved 1958) addresses–early on, there’s a discussion relating to the advantages of “unit construction” (which Ford was trying out with Lincoln & T-Bird for 1958):
“It is here proposed to introduce a vehicle construction which approaches the integral body-frame construction without entirely departing from the advantages of having the body and frame remain separate.”
The very curious can see the patent text/drawings here: http://www.google.com/patents/US2864647
Thank you; fascinating reading. It confirms what I have come to understand more and more: that the frames under most modern American cars increasingly became less of what they used to be before 1957 or so, and what they still are for trucks: a structure that can support various (or no bodies), without needing the structural interplay of the body.
Unibody construction was the hot new thing, and GM had already had quite a lot of experience with it in Europe, so developing a hybrid like this makes lots of sense.
A “unibody” is an aircraft monocoque space frame for a car. The concept was applied to houses soon after plywood was invented. Post and beam construction gave way to 2x4s and vertical siding. A modern house under construction is flimsy and fragile and perilously vulnerable to storms until after it is “sheeted”…which means the exterior covering is attached to the 2×4 exterior walls. A post and beam constructed house is as strong in the skeleton phase as it is when completed.
Sally, I know that GM was playing with the idea of going unibody for all Cadillac models except the new 1957 Eldorado Brougham. I think you may be misinterpreting the Patent though as it is for the floor pan design that matches up to the frame. If you look at the floor of a 1957 Cadillac sans interior you ill see the design matches.
A few things to compare with my old 70 C10 Chevy vs. my current 04 Nissan Titan. Steering column on Chevy is attached to steering box mounted about 1 foot back from front bumper, bolted to frame. It did have a type of telescopic column with shear pins to help prevent intrusion to some extant. The steering wheel was steel under hard plastic. The Nissan has a rack and pinon mounted to the firewall behind the engine, and also a universal joint type collapsible column with a padded wheel and 2 stage airbag. Gas tank (steel) in the Chevy was in the cab behind seat. Gas tank (plastic) in Nissan behind frame close to center of truck. Seat belts in Chevy, lap only although it did have threaded anchors for shoulder belts. Nissan 3 point belts for all except lap in front center. Front outboard belts have explosive charge to draw up slack in an accident. Chevy had no headrests. Nissan has 4. Nissan doors have side beams. Chevy has none. Nissan frame has collapsible points to allow crush space. Chevy has solid frame. Nissan has thick A pillars, so thick they can create blind spots. The Chevy pillars are thin, though with better vision as a result. The single cab in the Chevy with only A and B pillar vs. extended cab Nissan with thick A, B, and C pillar would be better in a rollover. The Chevy has 4 wheel drum brakes, the Nissan 4 wheel disc with ABS and EBD. I drove the Chevy 30 years without a major collision. And so far my luck has held out accident wise in the Nissan. I know which one I would want to be in if a major wreck happened. But damn it, I still miss my old Chevy. Thank you Paul for re-posting this well written informative article.
If trucks needed crumple zones, semi trucks and dump trucks would have them too.
Good summary ’67 conti. John, semis are so heavy that they don’t need crumble zones for minor collisions. But I bet you would find the death rate for single vehicle big rig accidents where they leave the road and hit trees or roll to be very high. They cabs are not very strong.
Small trucks are light and need crumble zones.
Until I saw this video, I had thought ALL GM full size car beginning in 1958 to the end of 1964 used the X frame.
When I was a teenager 50 years ago, I had car model kits of a 1957 Chevy, 1958 Chevy, 1964 Chevy, 1966 Chevy Impala SS, and a 1960 Pontiac Bonniville. Those models also had the frame details on the bottom, and from those model kits, I had assumed as a teenager that all GM full size cars from 1958 through 1964 had the x frame.
I also had a similar misnomer about Chrysler, Dodge and Plymouth cars back then.
My dad had a 1961 Desoto, and a 1957 Plymouth station wagon, both of which did not have full frames in which the body was the main part of the frame…I remember seeing that when ever my dad took those cars in for an oil change. From that, I had assumed that ALL Mopar cars went unibody in 1957…I recently saw a Wikipedia article that said all Mopar cars went unibody in 1960, except for the Imperial that went unibody in 1968. As for my dad’s 1957 Plymouth, Chrysler Corporation experimented building the 1957 Plymouth in unibody beginning in May of the 1957 production year (I have no idea if the 1958 and 1959 Plymouths went back to full frame until the 1960 models)…My dad’s ’57 Plymouth wagon was built in May or later in 1957.
This is the first I have ever heard of any sort of Unibody being associated with Chrysler Corp station wagons in 1957. Do you have anything to cite beyond your memory? As rushed as the 1957 models were in development I have a difficult time seeing how they might have worked some major unibody engineering into the schedule, and for a low-production body style, at that.
Just recently saw this article! Up until a few years ago, I assumed that all ’58-’64 full size GM cars used the X Frames! Then, after a little research, I found out that not all used it. This is the best article I’ve seen about this subject and clears up and answers all the questions I had in my mind! Thank You!!!!!!!!!!!!!!!!!!!!!!
I’m curious about the differences that may have existed between X-frames used by GM’s various divisions. Specifically, I recall reading somewhere that the Chevrolet X-frame was not very substantial, whereas the Buick X-frame was surprisingly robust – even though they looked very similar. Does anyone know if that recollection has anything to it? Or were the X-frames essentially the same at all divisions? I know similar debates have occurred over the GM V-8 engines of the 1960’s and early 70’s, and most would agree that each division seems to have developed its own unique engines, where almost nothing was interchangeable.
I found this on Pinterest. It’s safe to say both had engines. Though it’s not dated, the fact that so many guys have hats and ties, pretty safe to say rust should be minimal. Yet the damage to both the Brookwood and the Impala is pretty much the same as on the Bel Air. So I’d say the video is a fair representation of the real world back then.
However safe or unsafe these cars were, I’m sure that with enough bracing in the Fisher body (which, by that time, was not that different from structure a unibody car), the X-frame could have been as safe as any other frame design. But given that its mission was to preserve interior space under a lower roof line, the X-frame seems like a bit of a half-failure, at best. The floor in the front of a 1950 Cadillac looks at least 2 inches higher than the footwells in the rear, and with the roofline already down to 56″ (about the same as most Cadillac sedans from the 1960s to the 2000s, with the ’71-76 models being the lowest at 54.5″) , the front seating area looks a bit cramped from in the photos I’ve seen (although it seems that GM somehow managed to claim 43″ of legroom). Whatever the room in those cars, there would have been a lot more if GM had gone right to a full perimeter frame in 1957, instead of ’65, not to mention the gigantic transmission tunnel. The whole thing seems like a quiet fiasco.
Sorry, I meant to type “floor in the front of a 1959 Cadillac”; must have hit the wrong key. It’s so much easier to spot errors like that when you know that the whole world has already seen them.
Downstate N.Y. here. In the rust belt. Hated to put these cars on the frame contact lift back in the day when I worked at a service station. Bodies sagged. Had trouble opening and closing doors even on cars that were rust free. .
Andrew wrote: “They used a 1959 since that was the year this organization opened its doors.”
So, putting it cynically, this was a publicity stunt to show how much “good” this agency has done since? At least it is funded privately, by insurance companies, not by the Government.
Ehmmmm, when “private funding” is generated by selling a product that customers are government mandated to purchase, the distinction gets blurry.
I didn’t remember so many of the comments dealt with the 1959 Chevy Bel Air vs. 2009 Chevy Malibu frontal offset crash test conducted by the Insurance Institute for Highway Safety.
I retired from the IIHS a little over a year ago after a 40.5-year career with the organization. I witnessed the crash test in September 2009 as the main event of the Institute’s 50th anniversary celebration.
To set the record straight:
Because we were commemorating the 50th anniversary of the Institute’s founding, a 50-year-old car was a must to use in a crash test. The full-size Chevy was chosen because for nearly every year between about 1935 and 1979, the full-size Chevy was America’s most popular car. It was pitted against the most popular Chevy car in 2009, the Malibu (which was a newer design, although smaller and lighter than the old W-body Impala, and in fact, was smaller and lighter than the 1959).
The engine type wasn’t a criterion, but a 4-door sedan was a must because in 1959 as in 2009, that was the most popular body style. (How times have changed just since 2009!) An original, never restored 4-door Bel Air was found with essentially no rust. What you see flying out of the car in the video is dust, not rust. (It’s surprising how much hidden dust collects even in cars that are only a few years old, let alone one that is 50 years old.)
Back to the engine selection, it’s possible that in Chevy’s 1959 4-door sedans, the six may have outsold the V8. People mention Imperials, but other than in 1957 and ’64, they were barely a blip on the sales radar. We didn’t give any consideration to the possibility that the X-frame or inline six engine might affect the test results, but it seems highly unlikely.
I can assure you that the engine remained in the Bel Air for the test. However, we did conduct an earlier practice test using a 1960 Chevy Impala 2-door hardtop in very poor cosmetic condition but with a solid frame and inner structure. (I do not remember if this Impala had a 6 or V8.) We did have to weld in a new driver footwell and bolt in the front seat securely. The car was crashed against a flood-damaged 2009 Malibu. The results were were quite similar to those we saw in the publicized test and gave us the confidence to proceed with the latter.
And lot of discussion revolves around sheet metal thickness, but it’s not the exterior metal that determines a car’s crashworthiness, it’s the engineering of the inner structure that counts, as Paul mentioned in one of his comments. Also worth noting is that the driver dummy in the ’59 Bel Air recorded very high injury measures that likely would have been fatal to an actual person due to 3 factors: extensive crushing of the occupant compartment, severe rearward and upward displacement of the steering wheel and column, and lack of restraints (seat belts and airbags).
I’ve seen the 1959 Chevy crash test countless times. Yes I agree today’s cars are much safer, not only due to the crumple zones, better steel, better design, but also ABS, air bags, and the newer innovations such as lane assist, adaptive cruise, and so on.
I found this video of a 1962 Cadillac being crashed, for those who would want to see more automotive carnage.
https://www.dailymotion.com/video/x3t3or0
Tangent: There are comments from the original thread about the stregth of steel used for these X-frame cars v. modern.
Remember dent pullers? Am I correct in thinking that they’re not such a thing anymore for vehicles with modern crashworthiness compared to the BOF cars I grew up driving?
(I have been lucky enough to not do much in the way of field testing, but if I had to chose between pulling dents cheaply or much more survivable mishaps, I’ll take the latter.)
Wow, so many comments. Didn’t see mentioned that the X frame combines a unibody strength body shell, with a frame, in order to reduce noise, vibration and harshness. The combination together is pretty strong, and the isolated frame absorbs road impacts, noise, drivetrain vibrations, making for a much nicer car. All the compliments about late model cars ignores the fact that new cars all have unacceptable road noise. People probably don’t realize how bad the NVH is with new cars, until they drive an older model car, then jump into a new car and then realize the difference. Not sure how they did it, but even older unibody designs like AMC products and the Willys Aero cars don’t have this road noise like late model cars.
Steel-belted radial tires and stiff springs/sway bars are to blame. There was a mania in the Western world in the 70s that ordinary cars had to corner until your brain pressed against the inside of your skull, and to hell with ride and impact/vibration suppression, a fever which continues on common garden cars to this day.
I drove a RAV4 some years ago as a loaner car and every time it hit a bad bump my butt jumped off the leather seat (which was also hard). Rough bitumen vibrated the cabin. But it cornered. I couldn’t handle the rubber-band transmission either.
Let’s address the rust issue on the IIHS test. Here’s a newspaper report on an Impala and a Brookwood that hit head on. Don’t know exactly when or where, but we can tell from the clothes and the fact that both an Impala and Brookwood of the same year hit head on that it wasn’t too terribly long after production. We see much of the same damage on both that we saw on the Bel Air. I think this should clarify what the issue was for most people.
It’s interesting that Oldsmobile had used ‘improved X-Frame’ since 1933.
Source:
http://www.oldcarbrochures.com/static/NA/Oldsmobile/1933_Oldsmobile/1933%20Oldsmobile%20Brochure/image3.html
Thanks for drawing from the SAE/Cadillac info, Paul–it’s nice when we can precisely know “what were they thinking?” and don’t have to guess. This is a really fine essay!
(Hat-tip unnecessary but appreciated.)
It looks like the front footwells would much higher than the rear, or else have uneven floor under the pedals. We had a ’63 Impala until I was 8, and I don’t remember anything odd about the front floor, but I do remember the door sills being higher than the floor on our ’68 Buick.
Some of the ’57-8 Cadillacs had heating ducts for the rear compartment running through the bottom of the front doors and into the half B pillar. Took them four decades to do that again in the center.
I’m wondering if the complete change to console shift outside of pickups had anything to do with higher crash standards requiring a larger center hump for greater rigidity.
There are currently some EVs that have flat floors front and rear, as well as ICE-powered cars and crossovers with a flat rear floor, so I think not. I’m still confused though as to whether the floors in pre-1965 GM big cars are shaped differently to fit each division’s frame rails; i.e. a perimeter frame car having a distinct ledge at the outskirts, but a smaller center hump than in X-frame cars. The floor pans I’ve seen from this era don’t seem to be all that different from each other.
Don’t most EVs have the batteries in the floor, so they become part of the structure?
My FWD-only DTS has a small center hump in the rear, I guess for the exhaust pipe. It never made sense that when they could finally make the center seat flat and comfortable thanks to FWD, hardly anyone did. They sculpt them all for two occupants.
Pretty sure if my “tricycle” ((Hyundai)) , ans a “59 Chevy” crashed into one another, I’d be the “goner”.
Triumph used an X frame with light outriggers under their Herald/ Spitfire series of cars perhaps under a light car it worked better.
This got me remembering back to an accident my family was involved in 1962, where we were rear ended in a 1956 (?) Ford coupe, as we were stopped, my dad getting ready to make a right turn into our driveway.
The drunk drivers speed was estimated by police at 60 mph.
No seat belts, my mom had just handed my youngest sister (1yr) to my oldest sister (8yr) from the front seat, where my mom was holding her, to the back seat.
I can distinctly remember the impact, and both front doors flying open, and both my parents being launched out the open doors.
The drunk then tried to drive away, and was followed by other people, and I was told years later beat on the guy pretty good.
Us kids, all 4 of us were all ok, my dad was very lucky, thrown clear, but my mom had injuries, her head striking the curb, and was in the hospital around 3 weeks.
I was only 4 at the time, but I can still picture it, its like in slow motion.
I hadn’t thought about that in years.
Absolutely fascinating read, thank you!!! I googled the X-frame because I was consdering the purchase of a GM car of this era, and was pleased to read this history and explanation. Yes, the sacrifice of the 1959 Bel Air against the 2009 Malibu was memorable, but it was hardly surprising for anyone knowledgeable of the history of safety advancements in that interim between the manufacture dates of those vehicles. Personally, I think automobiles are be saddled with TOO much safety equipment that makes drivers feel “invincible” and drive poorly without any consideration of injury or death to themselves. On pet peeve is the size of the A-Pillars on a modern vehicle that seriously block views of traffic, especially at an intersection. I’d rather have a thinner roof pillar to avoid a crash as I am unlikely to flip a car.
But beyond the safety issues, the history is inriguing. I always associatd the X frame with Chevrolet and maybe Cadillac, but assumed all GM divisions used it. The details in this story set the record straight for me. Just a magnificent article for those of use interested in this period of design and engineering from the General.
Phil:
I wonder if the 1964-67 GM ‘A’s were cross frame. I remember riding in the
back of my grandfather’s 64 Skylark 2 door my parents inherited, and noticing
the front bucket seats in front of me either rocking back and forth depending on what we were going over, or even swaying inward toward each other and
outward! Maybe half an inch no more, but noticeable.
Not that those buckets of that time were particularly sturdy themselves –
my father was a tick under six feet and weighed maybe 150, and still the
driver bucket bottomed out under him. I’m over 190, and would probably
sit right through the floor board! lol
Was the X technique rigid enough, compared to box or ladder frame?