In a previous post, I talked about the unit body structure of the early Ford Falcon, Comet, and intermediate Fairlane. The 1965–1973 Ford Mustang, the early Mercury Cougar, and Ford Maverick were clearly related to the Falcon and Fairlane, but they departed from the formula in a number of ways with what Ford called “platform construction.” Let’s take a closer look at the structural design of the early Mustang, the original Cougar, and the ’70s Maverick/Comet.
Ford Mustang
As many Ford fans know, the very successful 1965 Mustang was preceded by the not-so-successful Falcon Sprint, a V-8 hardtop and convertible version of the compact Falcon, which was added to the Falcon line in mid-1963. (The V-8 also became optional on the Falcon Futura and Mercury Comet at that time, even on sedans.)
Preparing the lightweight Falcon and its Mercury Comet sibling for V-8 power, particularly in hardtop or convertible form, had demanded a lot of structural reinforcement, and required borrowing many pieces from the bigger, heavier Fairlane. This brought a substantial weight penalty (a Sprint convertible was 671 lb heavier than a basic six-cylinder Falcon 2-door sedan) and a lot of costly additional production complexity, which hadn’t paid off in sales. Falcon buyers weren’t terribly interested in the V-8, and the Falcon Sprint was a slow-selling commercial flop.
During the development of what became the Mustang, several early prototypes were cobbled together out of modified Falcon Sprints. Ford Division general manager Lee Iacocca and product planning manager Hal Sperlich were determined that their new car not share any sheet metal with the Falcon, but for a while, the thinking was that the Sprint could somehow be reskinned in a more appealing form. By the latter part of 1963, it was becoming clear that this was not going to work. According to chassis engineer Bob Negstad:
The first Mustangs were put together and sent out on “durability” — potholes. And they destroyed themselves. The body structure was terrible. There was a relatively small group of people who did this development part, the Make-a-Mustang-Out-of-the-Falcon-Sprint group. When the car started to have trouble, everybody scattered, disappeared. They said, “Oh my God. Here’s a disaster.” The few people who were the real movers and shakers behind the car, Hal Sperlich and Lee Iacocca, and the people who were stuck with this Mustang, we knew we had to fix it, do the development work.
The original Falcon had been optimized for minimum weight, and because its structure wasn’t originally designed to be a convertible, it was ill-suited even to a hardtop roof, much less a ragtop. Each new set of structural demands had involved more belt-and-braces fixes, so it’s not surprising that these test mules kept breaking.
Since the existing Falcon structure was not up to the task, even in Sprint form, this crisis led Ford engineers to evolve a new version of the Falcon structure, which they dubbed “platform construction.”
According to Jack Prendergast, the executive engineer for Light Vehicles during the Mustang’s development, “The platform-type frame, evolved from previous light-car experience, was designed to be really in the middle. All the various chassis components were attached to the underside, and all the body components were installed topside.” Negstad explained it like this:
The plan was very simple. We would make a convertible [prototype]. We added the structure to make a convertible, did all the testing, evaluating, twisting, and the durability. We fixed the convertible. When it came down to the coupe? … Piece of cake, put a top on a convertible and you’ve got even more stiffness. The Mustang coupe was too stiff. And that was a cost reduction … remove some parts [on the hardtop].
There were a number of precedents for this kind of platform construction strategy, but an interesting contemporary example was the Tipo 105 Alfa Romeo Giulia:
Like the Mustang, the Tipo 105 was unitized, but Alfa Romeo built the two-door version as a more or less driveable platform chassis-cowl structure to which the body was then welded. Alfa adopted this approach to make it easier for outside coachbuilders to add coupe or convertible bodies without needing to first cut away everything they didn’t need, while still giving the completed car the structural strength of a welded unit body shell.
If you looked at the underside of an early Mustang, its basic kinship with the Falcon was still evident, including the welded front rails and the rear torque boxes that tied the rear side rails to the sills. However, the underbody members seemed to have begun to melt together. This reflected the re-stressing of the structure so that the underbody would take on more of the load-bearing work, aided by the cowl and the lower sections of the body structure. (In particular, the rear wheel arches played a big role in tying the rear structure together.)
Even more than in the Falcon, the driveshaft tunnel in the floorpan provided a “backbone” for the Mustang platform. Note also the deep rear footwells, which served to further stiffen the floorpan. (The particular car whose floorpan is pictured above was originally a hardtop that was made into a convertible prior to its restoration, so it had the narrower hardtop sills; factory convertible sills were considerably wider.)
Where the six-cylinder Falcon had used a narrow crossmember just behind the transmission, the Mustang had a big heavy-gauge hat section beneath the front seats.
As Negstad said, a major benefit of this re-stressed structure was reducing the amount of additional reinforcement needed for the convertible. Convertibles still needed some, of course, but when the Mustang launched, the Ford press kit claimed:
Both the hardtop and convertible bodies are essentially the same, except that certain underbody members on convertibles use heavier-gage steel to compensate for absence of the roof structure.
The word “essentially” was doing a lot of work there, since the convertibles had significant underbody reinforcement, not just heavier-gauge steel, but a 1965 six-cylinder Mustang convertible added only 170 to 175 lb over a six-cylinder hardtop, much less than the 290 lb weight penalty suffered by a 1964 Falcon convertible.
The early Mustang convertible’s reinforcement turned out to be not quite adequate — from about November 1964, convertibles got additional tubular braces to reduce cowl shake.
The Mustang chassis was very similar to the Falcon in various respects, including the high-mounted front coil springs and the lower control arms located by diagonal drag struts.
As in the Falcon and Fairlane, the Mustang front end was a box-like engine compartment structure with steel side aprons welded to the front rails and the front suspension spring towers. The top of each side apron was folded over to form a stiff upper ridge, and the leading edges of the aprons and front crossmember were welded to the rectangular radiator support. (The front fenders bolted on over this structure.)
As in the Falcon and Fairlane, the spring towers were quite bulky: They had to be stout enough to absorb spring loads and braking torque and transfer them back to the body structure. The towers added strength to the front end, but as you can see from the above photo, they took up a lot of space in the engine bay, and they had diagonal braces (already removed from the car pictured above) to tie each spring tower to the cowl.
Even with a six-cylinder engine, the Mustang engine bay was somewhat cramped and obstructed, but using the diagonal braces to triangulate the spring towers against the cowl helped to stiffen the front end and absorb the braking forces exerted on the suspension towers in a panic stop.
Underneath, another set of diagonal braces between the front rails and the front crossmember strengthened the front end structure while also providing attachment points for the drag struts that formed part of the front suspension’s lower wishbones. The Falcon and early Comet used substantially the same layout.
As in the Falcon and Comet, the top of the fuel tank still formed the bottom of the trunk floor. The fuel tank was bolted in place, not welded, but the tank cell helped to stiffen the rear end.
Rear suspension was similar to the Falcon, although the Mustang used shorter four-leaf springs. There were compression shackles at the trailing ends of the springs, with rubber bushings that were supposed to soften the blow if the rear suspension bottomed out.
Like V-8 Falcons and Comets, an early V-8 Mustang was over 250 lb heavier than a six — the six-cylinder Mustang used a lot of Falcon parts, while V-8 cars substituted beefier Fairlane brakes, running gear, and suspension components. However, there were fewer structural differences between six- and eight-cylinder cars than had been required with the Falcon and Comet.
One area where Ford hedged on the early Mustang was front torque boxes. Both the Fairlane and the V-8 Falcon/Comet used torque boxes at all four corners, joining the front and rear underbody rails with the body sills and helping to absorb bending and twisting forces without transmitting them into the cabin. The early Mustang had rear torque boxes, like the six-cylinder Falcon and Comet, but only the early Mustang convertible had them in front. Ford claimed at launch that front torque boxes would make the hardtop too stiff, which was nonsensical; the real reason was almost certainly cost.
Closed Mustangs belatedly got a left-hand front torque box for 1967, but didn’t get a right-hand one until 1968.
Mercury Cougar
The original 1967 Mercury Cougar was a plusher, pricier version of the Mustang hardtop, which Lincoln-Mercury pitched as bridging the gap between the Mustang and the Thunderbird.
Although it had different sheet metal, an early Cougar differed little from a 1967 Mustang hardtop in its platform structure, down to the left-hand-only front torque box. (Cougar got a right-hand front torque box for 1968.) Unlike the Mustang, the original Cougar was not offered as a convertible, or with six-cylinder engines.
The biggest structural difference between the Cougar and the contemporary Mustang was a 3-inch-long wheelbase. Unlike the early Comet, which had put its extra 4.5 inches of wheelbase behind the rear seat and had no more interior room than a contemporary Falcon, the Cougar added the extra space within the cabin, providing a bit more front legroom and an additional 2 inches between the front and rear seats. I think the reason Lincoln-Mercury was willing to do this for the Cougar and not for the Comet was that the Cougar was only offered in two-door form — there was no need to tool for unique rear doors for a four-door sedan or wagon, which would have been a lot more expensive.
Aside from additional sound insulation, the Cougar had a few suspension tweaks for greater isolation. In back, the axle was attached to the springs by flexible “iso-clamps” (something Ford had previously developed for the Lincoln Continental and then the Fairlane). The rubber bushings at the leading end of each rear leaf spring were now “voided” (with small holes in the rubber) to make them even softer, helping to absorb spring harshness.
In front, the drag strut that located each lower control arm now had an articulated joint, giving the front suspension more ability to shift fore and aft in response to vertical bumps.
These features were really more in the realm of suspension modifications than structural changes, but they made the Cougar feel more solid by reducing the amount of noise, vibration, and harshness transmitted through the structure.
Both the Mustang and the Cougar continued to use this platform through 1973. There were some additional changes in subsequent years, many of them prompted by federal safety regulations, and the Cougar spent 1971 through 1973 on a slightly longer 112.1-inch wheelbase. I’m not going to try to get into all those changes here, since some of them would also require explaining the related motor vehicle safety standards.
Ford Maverick and Mercury Comet
In April 1969, Ford introduced the compact Maverick, which would shortly take over for the moribund Ford Falcon in the U.S. Ford lineup. As I’ve discussed in a previous post, the Maverick was a fairly dismal penalty box of a car, although it sold very well on the strength of its sleek styling and low price.
Contemporary car magazines found nothing very interesting to talk about when it came to the engineering of the Maverick, and I had to dig up an analysis from the British journal Automobile Engineer to find many more details than were in the brochure.
American buff books generally dismissed the Maverick as an early Ford Falcon in a Mustang-ish new outfit. In fact, Ford considered the Maverick a new variation on the platform construction concept developed for the Mustang. Like the Mustang and early Cougar, the Maverick carried much of its structural strength in the underbody, in particular in the unusually thick side sills. Automobile Engineer, examining Ford data on the roof structure, remarked that it “seems to suit methods of assembly rather than afford rigidity.”
While I doubt that a Maverick convertible was ever on the table, even as a proposal, the platform construction concept probably provided greater styling flexibility — sporty styling was one of the Maverick’s few non-price-related virtues.
As with 1968 and later Mustangs and Cougars, the Maverick had torque boxes at all four corners, with no more nonsense about their making the car “too stiff.” It also had an asymmetrical rear powertrain mount (which you can see above), allowing space for the exhaust pipe to be tucked close to the driveshaft. Unlike the later Falcon/Comet and Fairlane, which hung this mount on “boomerangs” hung off the front torque boxes, the Maverick rear mount was bolted onto the U-shaped crossmember that connected the front rails.
Strictly speaking, the Maverick wasn’t a scaled-down Mustang any more than it was a restyled 1960 Falcon, but in a structural sense, it was closer to the Mustang than the Falcon. This isn’t to say the Maverick shared any sheet metal or significant structural components with the Mustang — I doubt that it did, although the cars shared various other components — but the ability to share production facilities and tooling would have been worthwhile. Ford was still making Mustangs in substantial numbers, whereas the original Falcon had expired in 1965. (The 1966–1969 Falcon had really been a truncated Fairlane/Torino, as I discussed in my earlier post.) The platform construction approach had also benefited from a decade or so of additional Ford experience in unit body engineering, plus the availability of new computer tools for structural analysis.
Despite all that, the Maverick set no new records for packaging efficiency — the low roof and semi-fastback shape saw to that — and it wasn’t outstandingly light for its size. The body in white was 21.5 lb lighter than that of a 1960 Falcon, which had been somewhat bigger and had a longer wheelbase, but the Maverick’s base shipping weight was 242 lb heavier. Admittedly, the Maverick did have a standard heater and emissions controls (and its front end was designed with an eye towards controlled crush in a frontal impact, not something Ford considered when the Falcon was designed a decade earlier), but its interior and features were spartan. The original Falcon was not a particularly nice car as cars went, but it had been impressively efficient and impressively cheap; the Maverick was mostly just cheap.
As with the original Falcon, everything Ford subsequently did with the Maverick seemed to make it heavier. By 1977, its final year, a basic six-cylinder Maverick had gained over 300 lb, only part of which was due to its heavier 5-mph bumpers.
From 1971 through 1977, there was also a Mercury version of the Maverick, the Mercury Comet. It had no significant structural variations that I know of, differing from the Maverick mostly in its hood, grille, and taillight treatment.
At some future date, I might try to dig up some more technical information on how Ford transformed this platform into its final iteration, the Ford Granada, Mercury Monarch, and Lincoln Versailles, but I think I’ve already kicked the Versailles around enough for the time being.
The thing to take away from all this is that these different unit-body compact Fords were not so much a single common platform as sets of related concepts of structural and chassis engineering. Ford actually regarded these cars as several distinct platforms — Falcon/Comet, Fairlane/Meteor, Mustang/Cougar, and Maverick/Comet. They were very similar in chassis design, and they shared a lot of mechanical components (and probably a fair bit of basic tooling), but in terms of structure, they were cousins rather than siblings.
Related Reading
CC Tech: Ford Falcon, Comet, and Fairlane – How These Unit-Body Fords Were Alike (And Different) (by me)
What sort of structural difference was there between the Maverick coupe and 4-door sedan? In the latter case it was stretched *back* to the original Falcon wheelbase, but no doubt was heavier yet.
“As in the Falcon, the top of the fuel tank still formed the bottom of the trunk floor”. I seem to remember that part of the Pinto’s fire problems were blamed on the fuel tank/trunk floor. Ford had been doing it since 1960? I don’t remember that being brought up (retroactively) at the time, but I’m not a Ford fan.
That combination fuel tank/trunk floor was a really bad idea from a safety standpoint. Granted it’s all a matter of degree and it only happens in extreme circumstances, but there is a big difference between a ruptured fuel tank spraying gasoline on the outside of the body structure vs. spraying it on the inside of the body structure in a heavy rear-end impact.
A fairly common upgrade to early Mustangs is a steel firewall that goes between the trunk support brackets under the back seat and the rear seat backrest.
It’s a well-known “little known fact” that Pinto wagons didn’t have the coupes’ safety problems. I wonder if part of that is due to a separate load floor.
The Pinto platform was VERY different structurally from the Mustang, Maverick, or Falcon, and its fuel system vulnerability is not comparable.
If you were talking to me, I was thinking of how long they were able to “get away with it”. It looks horrible to me but it took a decade and a Pinto (designed post-Nader) to actually make it dangerous. Structurally it looks better than a hung tank. Still…
The drop-in fuel tank in the Mustang (which was also used in the Falcon and Comet) has gotten lots of criticism over the years for safety and fire danger. However, it was NOT the same design, or the same issues, as the Pinto, which had a completely different structural design and a DIFFERENT set of safety problems related to its fuel tank. The two problems were not related except philosophically (insofar as they illustrate Ford’s callous attitude toward fuel tank safety).
This is interesting – I had never been aware of how different the structure of the early Mustang was from the Falcon. The one thing I remember from my 68 Mustang hardtop was how Ford routed the steel fuel line through the front torque box on the drivers side. The holes front and rear probably contributed to extra fast corrosion in that box, and was probably why the hidden part of the fuel line started leaking on my 11-year-old car.
I’ll always choose the Cougar. It’s practically a perfect car.
Superb article, especially appreciate the images that are really on point.
The fuel tank seems to be in a quite exposed position; I imagine in case of a rear hit, the bolts would fail and the tank drop?Seems to be a high risk of a leak (certainly not the only car of the time with this “characteristic”)
On a separate note, I have always preferred the first gen Cougars to the same-period Mustangs: more refined for a very reasonable price increase, and if one wanted, it could have the Boss 302 or the CJ
A big difference in the early Mustang convertible structure is that the rocker panel protruded into the passenger compartment. I learned this when a Mustang supplier accidentally sent me convertible kick panels when I ordered them for my coupe, and they were significantly shorter. The seat hats are also different between the two bodystyles, with the convertible’s being welded all the way across the floor.
Nice discussion, Aaron. I’m not sure I’ve seen anyone get into this topic as thoroughly.
Yes, and those substantial sill reinforcements essentially negate the quote by Negstad in the article:
Both the hardtop and convertible bodies are essentially the same, except that certain underbody members on convertibles use heavier-gage steel to compensate for absence of the roof structure.
That’s clearly not exactly the case. Those are substantial sill additions added to the platform. Seems like Negsted should have known that.
The quote is not from Negstad, nor did I say it was — it’s from the engineering press kit that Ford issued in April 1964 for the Mustang launch.
Ah yes, I see. But the earlier quote from Nested still seems to be contradictory:
The plan was very simple. We would make a convertible. We added the structure to make a convertible, did all the testing, evaluating, twisting, and the durability. We fixed the convertible. When it came down to the coupe? … Piece of cake, put a top on a convertible and you’ve got even more stiffness.
Adding sill reinforcements was the most common (almost universal) way to reinforce an existing roofed body for use as a convertible. This rather contradicts his quote and claim.
He went on to say that they decided the coupe was too stiff and they removed some things from the hardtop for cost reduction. I truncated it because the way he described it made it sound like it was a change made between the “1964½” cars and the 1965 model year; THAT part was incorrect, and misleading.
In any event, what Negstad was saying was that they developed the PROTOTYPE for the Mustang convertible first and then scaled back some of the structure for the hardtop.
Are you suggesting that these large sill reinforcements were part of the original hardtop body and then removed? I find that hard to believe. Those look like classic convertible reinforcements.
No, I’m saying that Negstad was talking about the development of the Mustang PROTOTYPE, and said that they started with the convertible and then looked at what they could scale down, scale back, or remove for the hardtop.
Well, seems like something fairly significant changed along the way then from prototype to production. These look like they were added to the coupe floor. But enough of that. I’ve long learned that there’s often a difference between the verbal historical record and the photographic one. I’ve learned to lean on the photographic one a bit more as it doesn’t tend to suffer from human interpretation or memory shifts.
My ’64 Corvair convertible also had much wider rockers than my neighbor’s ’62 coupe. They also served as heater ducts so if I turned the heat on during a rainstorm water would pour onto the floor.
Upon further examination of the restoration shop project description, the car in those pictures was a strange hybrid: It rolled into the Metalworks shop as a convertible, but it had actually been previously converted from a 1965 hardtop, so its original sill and floorpan structure was the hardtop version. (The floorpan and much of the underbody structure was replaced in the process.)
I confess it hadn’t occurred to me to think it might be a converted hardtop, since the extensive and obviously very costly restoration it received is way beyond anything I would think someone would want to give to an old aftermarket conversion, but that’s why the original floorpan looks like the hardtop, not the convertible.
Having owned a number of those cars, a 1964 Falcon with a factory 260 V8, fully synchronised 3 speed and factory AC, a 1966 Shelby GT350 (Mustang body with both engine and chassis upgrades for racing). Last was a 1970 1/2 Falcon station wagon. Prior to January 1st 1970, it would have been sold as a Fairlane, same body, just had Falcon on it.
The 1964 Falcon was built July 27th 1964, nearly 4 months after the Mustang came out. It had a number of Mustang parts on it, the 260 V8 had 289 cylinder heads, all the gauges had Mustang part number prefixes, I went to replace the lower ball joints, had to buy Mustang lower control arms.
Here is what replaced the 64 Falcon, picture was at an autocross (gymkhana) behind a now long gone Montgomery Wards on a Sunday afternoon.
A bit off topic, but anyone notice how out of alignment the left front tire is on the Cougar in the top photo.
Lots of negative camber.
VW used a platform frame with tunnel for reinforcement, but of course the body was bolted on as opposed to being welded.
I’m sure there was a platform frame prior to that but I can’t say what it was.
We stand on the shoulders of giants, or at least a number of like-sized individuals.
Aaron, great analysis..but in working to save a few cents (and increase profits) making the gas tank a structural member and the floor of the trunk of first gen Mustangs cost many lives. Watching the FMC period film footage of fuel sloshing into the passenger compartment in a rear end collision is sickening.
Enjoy the technical engineering details and really getting into the weeds on stuff like this, and especially chassis and engine design that’s usually hard to find in typical car mags and brochures.
This two part series on the Falcon and it successors has been wonderful. Thank you Mr. Severson.
For me the key sentence is: “The platform construction approach had also benefited from a decade or so of additional Ford experience in unit body engineering, plus the availability of new computer tools for structural analysis.”
An entire article (or a series) could be written on how computers revolutionized automotive design in the 1960s. Design work on the Falcon probably began around 1956 or so and would have been done with slide rules, hand drawn charts and graphs, and lots of tril and error testing.
Faster computers with improved storage were the norm throughout the 60s. The IBM 360 system came out in 1964. At that point engineers would have had enough computing capacity to do meaningful design analysis. Also, numerous other vendors were selling good quality computers that seemed almost purpose built for structural analysis.
Also, lets not forget NASA. The Apollo program was in full swing and millions were poured into mathematics and computer programs for the dynamic analysis of complex structures. Since one of NASAs stated goals was technology transfer to the private sector I am sure that Ford and all other manufacturers made good use of the latest developments.
I expect that a structural design engineer who went to work for Ford in 1970 probably owned a slide rule I’ll bet that he never used it. I’ll also bet that he could write Fortran code like nobody’s business.
Ford (and Chrysler and GM) already had computers to perform suspension geometry and certain structural analysis problems in 1958–1959, when the Falcon was designed. I was just looking at a 1960 Ford technical paper talking about it, although it doesn’t say anything about the computer hardware, just that it was programmed to extrapolate coordinates and compute camber, caster, and spring length throughout the range of suspension travel (outputting on punch cards, naturally). Compared to what they were able to do later in the ’60s, the computer analysis was rudimentary, but the U.S. automakers had already started using it.