Chrysler moves to Unibody (unit-body construction): 1960
In 1960, most Chrysler Corporation cars moved from body-on-frame construction to a unit-body design; the rest, other than Imperial (1967), moved in 1961.
The move was unprecedented in scale: no company of Chrysler’s immense size had done this before, certainly not with all of its high-volume cars at once.
The move was also surprisingly uneventful. While simply changing body styling had resulted in a disaster for the 1957 cars, and changes to the Valiant (renamed Volare) brought about a similar disaster in reliability for 1976, the much more dramatic change to Unibody seemed like a quality non-event.
One reason for this was extensive testing. Pete Hagenbuch said, during a tour of the Walter P. Chrysler Museum:
This is a body model that they used to use in the stress lab. They used to build one of these for every body shell we ever tried to develop, and in clear plastic, it’s a very accurate model of that car. We used to see them all over. The stress lab was just one building north of the building I used to spend a lot of time in, and you used to see these things everywhere. They’re looking for the high stress point, something where they need to smooth it up or beef it up, or both. That is something the computer does today.
Chrysler was not the first company to make unit-body cars, by a long shot; but they were the first to mass-produce unit-body cars which had been designed with the help of computers, thanks partly to their extensive military work, which made electronics a “home strength.” They were also the first to use unit-body cars whose exterior sheet metal was not required to provide structural strength; that had been a major problem for Hudson’s early unit-body cars.
Chrysler was also the first to use a seven-step series of body structure rust proofing bathes using electrostatic charge to bond sealant to the metal. The latter was required partly by the need to keep the sheet metal solid for strength, but, one suspects, mainly because of the disastrous 1957 cars.
Overall, the system worked. To quote Curtis Redgap, “The new unibody made all the Chrysler lines ride solid, rigid, and silent, with no rattles or squeaks. To achieve this in a fleet car was truly astounding.” Critics noted that the Chryslers had superior cornering (compared with their American counterparts) without sacrificing ride.
1960 was not the first time Chrysler launched unitized bodies; the 1934 Airflow had a sort of unitized body, with a weaker than usual frame, and body framework welded to the chassis to provide stiffness. That said, the 1941 Nash 600, according to historian Bill Watson, the earliest predecessor of the modern unit-body car; Nash, incidentally, later merged with Hudson to form American Motors, which was acquired by Chrysler in 1987.
Lanny Knutson wrote for the Plymouth Bulletin:
There was a frame, however - a subframe, bearing the engine and "Torsion-Aire" front suspension, that was bolted to unitized body. This arrangement allowed the front fenders to be more easily removed for repair or replacement than those of the completely unitized Rambler. ... One of unitized construction's drawbacks is that no sound insulating material can isolate the body from the frame, bringing road noise into the cabin. To counter this problem, Plymouth developed extra large rear spring bushings, a new exhaust system hanger, and a driveshaft designed to reduce high-speed hum. Special sound deadening fiber matting and liquid-applied coating contributed to making what could have been “riding in a tin can” into a pleasurable experience of traveling in a car far quieter than those of then-conventional construction. And, of course, the engine was mounted on its own frame, separated from the body by the usual sound deadeners.
With its 1957 models already rusting out, Plymouth had to confront the rust problem in a big way. The spectre of a rusting-out unibody with no frame to hold it together was simply too scary to contemplate. A series of six chemical sprays and seven dips into chemical baths plus four coats of paint prevented rust where its damage could be worst - on all those structural inner beams. The wheel wells, exposed as they were to road salt, still proved to be subject to rust, however.
Plymouth advertised its Dura-Quiet Unibody with over 5,400 welds. The other divisions simply called it “Unibody.” Dodge claimed that the 1960 Dodge’s unibody construction was “twice as strong and twice as tight as ordinary body-and-frame construction. Braced in every direction with rugged box-section crossmembers, the Dodge Unibody enclosed the passengers inside a rigid framework of steel.”
The modern unibody construction was, according to his obituary, created by James Murie Callison; he fought as a Marine in World War II, then worked for Ford and then Chrysler. Jim Callison retired in 1981, and died at the age of 91 on March 13, 2009.
1960 DeSoto brochure boasting of Unibody achievements
(Via J.P. Joan’s Chrysler Literature group): Engineers have known for years the virtues of unit-body construction. With frame and body a single unit, rattle-causing nuts, bolts and washers could be eliminated . . . frame side rails could disappear with no loss of protection . . . interior roominess, comfort and road-ability could all be greatly increased. Perhaps most important of all, a welded single-piece body-frame unit resulted in tremendously increased strength for the entire car. And the car stayed strong, silent and rattle-free for years. It was a better, safer car when it was new and for as long as anyone would drive it.
It took years of research and development to make such a system both practical and acceptable to the tough quality standards of Chrysler Corporation engineers. For 1960, De Soto introduces the Unibody, exclusive in our price class. It has 40% greater resistance to up-and-down stresses and 100% greater resistance to twist. It is everything we hoped for—and more!
You will notice the difference the moment the car begins to move. There is a new sureness and steadiness. You will feel the great strength and safety in the firm, solid way it smooths the bumps — the flat, ground-gripping way it glides around sharp curves. Unibody has helped make this possible—but it's more than that . .. it's Unibody in combination with Torsion-Aire Ride that has worked this miracle.
Other cars (mostly small cars) have unit bodies. Other cars (mostly European cars) have torsion bar suspension. But only DeSoto in its field combines Unibody, torsion bars and extended rear leaf springs to bring you a totally new experience in automobile riding . . . a ride you couldn't have had before at any price. You simply must drive the new De Soto to appreciate it.
Head room and leg room have both been increased. This alone would make the car more comfortable. But that's only part of the story. The additional room has allowed us to make your seating posture more natural and more comfortable. To make getting in and out easier than ever, door pillars have been redesigned and repositioned, and the doors open wider.
Some of our engineers think the thing you'll notice most in the '60 De Soto is the almost complete lack of noise, even at cruising speeds. The new Unibody itself plays a part in this, along with more insulation in more places which is now possible with Unibody. This is important to you for more reasons than you may think. It is a fact that noise is nerve-racking. Noise from the engine and the road in an ordinary car is one of the most important causes of fatigue. The lack of noise in a 1960 De Soto means you can drive further and arrive feeling fresher.
Tighter seating of windows and doors is now possible, to keep your new De Soto warmer in winter and dry in the most driving rain. Sealers and weatherstrip ping have been improved in quality, too. And Unibody is easier to inspect, simpler to repair. This saves you time and money.
Protection against rust and corrosion has been revolutionized. Each underbody is dipped seven times in rustproofing chemicals and protective coatings. This means longer life for your new DeSoto.
Feature for feature, the 1960 De Soto Unibody offers you a new quality combination that simply cannot be equaled. And it's standard equipment on every new De Soto at no extra cost.
The Chrysler unit-body press release (published on September 18, 1959)
Science and electronics telescoped years of design computations in new Chrysler products to produce best bodies in the Company's history
An “electronic proving ground” furnished design engineers with the structural strength secrets of the 1960 Plymouth, Dodge Dart, Dodge, DeSoto, and Chrysler while they were still on the drafting boards.
Electronic computers handled in a matter of months millions of design calculations that would have taken years to solve by slide-rule methods. This electronic assistance made it possible to evaluate countless different advanced design features and select the best ones for incorporation in the new cars.
The new 1960 body designs resulted in measurable gains in overall strength. In static structural tests conducted in the engineering laboratories, the new four-door sedans show a 100% improvement over conventional body-and-frame construction in torsional rigidity (resistance to twist) and a 40% increased beam strength. Combine the inherent strength of the unit body, increased room for passengers, superior entry and exit space, and new heights in silencing and sealing, Chrysler’s exclusive new rustproofing treatment, and the result is body engineering progress equivalent to that brought to chassis design by the TorsionAire suspension.
Chrysler’s Unibody construction imparts an extremely solid feeling to these new products. During extensive torture tests on the roughest roads at the company's proving grounds, prototype models surpassed all previous durability records. The new car structures withstood a gruelling night and day pounding from three to four times as long as predecessor models.
Unibody is a text-book picture of design efficiency at work — minimum weight with maximum strength, encased in modern low-silhouette styling.
Constructed Like a Bridge
The body is framed like a bridge truss, with sturdy box sections of heavy steel extending upward from the sills, along the roof over the window openings, and downward again at the rear to a solid foundation in the rear wheel housings. Connecting these two structural trusses are rugged transverse members, spanning the unit body at the floor pan, cowl and at the upper and lower edges of the windshield and rear window.
The front structure and the radiator, fenders, shields and panels are integrated into an effective unit.
At the rear, fully boxed longitudinal framing members and transverse channel sections support the drive and rear suspension elements, adding to general body rigidity. Chrysler’s construction features heavier sills — in many cases two to three times thicker in underbody areas — than the previous models. Bulkheads are welded into the sills to provide even greater strength.
Door pillars, too, are much stronger in this body. Windshield corner posts are slightly arched with no “dogleg” to impair their load carrying ability. Nor is there any obtrusive projection of the lower windshield corner into the front door opening on Chrysler Corporation cars.
New, stronger hinges assure proper door alignment for the life of the car. The entire cowl area is exceptionally rigid, rear pillars are stronger and there is additional reinforcing in the rear quarter areas.
Computers Widely Used
Development at the superior new bodies was greatly accelerated by using electronic computers to determine the inherent vibrations of the engine and the road-induced vibrations which had been transnlitted to the unit body. After millions of electronic calculations, they arrived at a system of engine mountings — using soft rubber and coil springs so that the engine vibrations cancel body vibrations. This, then, is the new Chrysler “tuned” body structure which banishes shake, rattle and squeak from automobiles.
To develop even further the strength of the Unibody, plastic miniature prototypes, scale replicas of the 1960 cars were built. In each clear plastic prototype, some 5,300 spot and seam welds and 61 feet of gas and arc welds were simulated, representing the strength characteristics of a full-scale body. Use of these models made it possible to measure stresses set up in the unit body under various conditions and full-scale steel bodies were designed to meet these stresses.
To this concept of automobile construction, Chrysler has added an anti-corrosion process that involves seven external and internal body dip sequences with six spray operations, and seven external paint finishing operations. This provides the unit body with the finest corrosion protection to combat the costly, persistent problem of rust.
Similar anti-corrosion procedures, chemicals and paints are used to rustproof Imperial bodies, but craftsmen at the Imperial plant use an even greater number of spraying operations in the rustproofing and body finishing process.
As a final rust preventive measure on all 1960 Chrysler Corporation cars, a special lance is used to spray-coat the interior surfaces of panels below the doors with a high melting point wax that forms an additional, permanent protective layer in this critical area.
New Sealing Techniques
Chrysler engineers also did something about bad weather. They sealed it out of the 1960 cars. Seams and joints are redesigned in the new bodies to do a complete job of keeping water out. A newly-developed rubber-base sealer expands under the heat of welding and subsequent enamel baking operations and is forced into the most remote points of the body where it remains for the life of the car.
Exclusive this year with Chrysler Corporation cars is a single "key-hole" opening to carry all wires and cables through the front firewall. This single keyhole, sealed by a vinyl collar, eliminates noise and dust admitted by usual Swiss-cheese arrangements of holes in the wall between the engine and passenger compartments.
The engineers also took a design cue from jet plane instrument mountings to set the rear portion of the new engines on rubber and coil springs to reduce vibrations.
Generous use of the latest and most effective types of sound insulating and weatherproofing materials, combined with the advances in the body structures make the new Chrysler-built cars the quietest, most solid feeling and best riding ever produced.