Around the beginning of March a cost estimate was submitted to Opel who by the end of April contracted Brissoneau & Lotz for the actual study work on production methods and tooling and for the building of the first two prototypes. Since the onset of the contract it was agreed that Brissoneau & Lotz would deliver the bodies in painted and trimmed condition, ready for the installation of mechanical components.
In July 1966 Brissoneau & Lotz sub-contracted Chausson to develop the body-in-white and relevant dies and assembly fixtures. The rest of the year was spent on program refinements while Opel was at work on deciding the modifications to be introduced on the Kadett underbody assembly. Among others, one decision was to back up the engine 40cm to improve the load distribution ratio and, another, the adoption of rotary headlamps instead of the pop-up units used on the prototype.
In this agreed layout, the body started its active design phase in January 1967. Opel's job was to modify and finalize the underbody assembly, or better, the "platform chassis" to which an additional cross rail and longitudinal beams were added, also because of the backed-up engine location.
The estimated delivery time for the first body prototype was the end of May 1967. To save time, the development of some accessory items was assigned to Chausson, for the broad concepts at least. These included the glazings, window lifts, heating system, and the headlamp rotation mechanism whose finalization was intimately bound to the configuration of the body itself.
This stage gave rise to a close and effective cooperation among the engineers from the three firms involved. Since the very beginning, the main obstacle was represented by the dashboard/instrument panel design; the need of having it accommodate the heater with its ductings, windshield wiper mechanism, instrumentation, radio housing, air distribution ducts and outlets, implied a high degree of concentration (further enhanced by the bulk of the backed-up engine) such as would certainly not facilitate the task of designers.
The instrument panel resulting from the above requirements could not possibly be plain and simple, and was designed for one-piece molding by the ABS skin with incorporated metal inserts technique. Also, the wealth of on-board equipment with its many variants involved a rather complex electric system which was designed by the Engineering Center of Brissoneau & Lotz.
As to sheet metal paneling, some problems had to be solved for the unitized body manufacturing schemes. After breaking down its entire surface into panels, using the first plaster mock-up, it became evident that the extremely "pure" body lines would not have tolerated any in-view welds. The presswork and assembly specialists then decided to adopt inert gas (Argon) welding; this, of course, meant the unavoidable shortening of weld seams as far as practicable and compatibly with the pressing requirements.
At the same time, the true scale projections of underbody and the ones of the body shell were traced on mylar sheets (a stable and undeformable plastic paper). All the aprons and panels of the dashboard and firewall, front wheelboxes, radiator support, etc. were defined on the first drawings and all the other boxed-section elements on the second ones.
The outlines needed for the preparation of master models for prototype parts production were obtained by placing the Mylar sheets in contact with previously sensitized metal sheets, using the direct transfer technique. Generally speaking, the performance figures laid down for the car and its possible use in sports events had imposed on Chausson, since the early design stages, the need for painstaking care in establishing the body shell strength factor. True as it was that the lack of apertures in the rear deck represented an advantage in this sense, the thinness of windshield pillars—a design "must" with no exceptions—led to complications in the body shell development stage.
As mentioned earlier, the accommodation of accessory equipment items resulted in three main problems of difficult solution: the heating system with its considerable bulk (because of performance demands), the windshield wipers with concealed linkage, and the rotary headlamps which had to meet the American safety standards requirements.
The heater—developed in cooperation with Sofica—was finally mounted on the right hand side, behind the instrument panel, with air intake in the cowl cavity.
For the windshield wipers the requirement was twofold; meet American standards on sweep area and the styling demand for concealment of wiper arm pivots under the hood. The one-piece drive gear and control linkage, also housed in the cowl cavity at the foot of the windshield, facilitates wiper installation on the assembly line and any subsequent action if needed.
Regarding the headlamps, although their rotation about a longitudinal axis had proven to be the best solution as to proper photometric and aiming performance, it was necessary to keep in due account also the American standard which required an operation time of less than 3 seconds and positive locking in the "open" and "closed" positions.
The control system designed (and patented) consists of two pinions made integral with the revolving "cases" and in mesh with two toothed sectors coupled to a cross bar in turn operated, through a cable, from a hand control lever fitted on the transmission tunnel. The headlamp rotary case is provided with a detent which, at end of travel, engages two latches of the automatic clearance take-up type, one for the "open" and one for the "closed" position. When the headlamps lock in "open" position, the hand lever actuates a microswitch which turns the lights on. It is thus impossible to switch on the headlamp beams during rotation and in case something goes wrong in the maneuver a tell-tale light on facia will glow to warn the driver.
Some difficulties have also been encountered from the manufacturing standpoint. The front fenders, in particular, though not having any extensions, were characterized by a rather unusual depth and bulginess of wheelboxes. The apertures for the two air intakes in the nose have complicated the pressing of a single panel whose configuration, after all, was not too complex. The marked curvature and wide area of the body side panels have imposed extremely careful attention to presswork cycle details.
The door panels, and window frames, had to be made from three pieces. To facilitate the body shell pressing and assembly operations, the Chausson engineers have had to ask Opel for reconsideration of the quarter window recessing depth, the design of the air intakes added to the front end panel and the adoption of a garnish plate to conceal the jointing around the rear transom panel.
Following is a detailed description of the assembly sequence:
Under body or platform chassis:
Components in common with the Kadett underbody are supplied separately, except the frame consisting of rear side rails, seat cross rail, and shock absorber anchoring brace. Floor assembly starts with the front side rails and central beams, rear frame, tunnel, front cross rail and seat supports. Next, this sub-frame is fitted with the different aprons, cowl-dashboard-firewall assembly, front wheelboxes pre-assembled to the fender cross ribbings, radiator support panel and air intake ducting, forming an assembly incorporating the whole fore section framework.
The body side framework, pre-assembled on jig away from the line, includes the rear wheelbox inner side panellings, outer wheelbox panel, rocker panel, front post, windshield pillar with reinforcement and hardware, and roof cant rail.
Main Assembly Jig No. 1:
On the under body are fitted the two body side frameworks, interconnected by the back window and windshield upper and lower cross rails and the rear window sill panel. This jig is equipped with numerous tiltable gauges for checking the proper location of the different components, particularly the opening contours.
Body Outer Paneling:
They are divided into two subassemblies which call for specially designed jigs for the inert-gas welded area trimmings. The fore-section includes the two fenders and front end panel whose cross rail and the two headlamp housing shells in turn incorporate the lamp front swing pivots and control mechanism attachments. The aft-section consist of the side, roof and transom panels. All welds are sanded and filed smoothly until they are "invisible."
Main Assembly Jig No. 2:
Practically identical to No. 1, this jig is intended mainly for the "dressing" of the shell with the fore and aft paneling assemblies, and is fitted with the necessary provisions to ensure the perfect alignment of the headlamp orientation pivots.
Upon leaving assembly jig No. 2, the body shell is mounted on a turnover platform on which the front end paneling application and weld trimming operations are carried out under optimum accessibility conditions.
Opel has always devoted great attention to corrosion protective treatments and although the body will later be dipped completely in a solvent bath, many component parts are coated with a zinc-based paint in the welding areas and a chromate-based paint in unwelded areas. This protective treatment is made on a special line where the overhung elements are first degreased and dried, then painted and dried in oven.
Hinged Panels Fitting:
After the weld finish stations where the tin brazings are made, the body passes onto the hinged panels fitting lines for installation of the doors and engine hood, the whole body being checked once again.
The above presswork operations are performed at the Chausson plants at Gennevilliers. The in-white bodies, suitably oiled for added protection, are fitted on dollies and carried on to special trailers (eight to each) to the Creil plant where Brissonneau & Lotz will take care of the body surface treatment, paintwork, ,trimming and finishing.
Surface Preparation Treatment:
After going through the acceptance inspection line, the bodies are hooked up onto the surface preparation treatment line conveyor system. They are first automatically cleaned, then degreased, rinsed and iron phosphate coated; next, they are dried and completely immersed in a solvent bath. The entire surface of the bodies—both internally and externally—is protected by a rust-inhibiting compound coat.
Priming and Sealing:
Following the above preliminary processing of the metal surfaces, the bodies receive a first coat of primer which is dried in an 80-meter long overhead oven kept at an average temperature of 180 degrees Celsius throughout. On coming out of this oven the underbody panelling receives a sound deadener coat serving also as further protection against corrosion. The next step is the application of the sealant "Strings" intended to ensure the perfect water-proofing of the body. The sealant strings are then polymerized at 100 degrees Celsius in a special curing engine.
At this stage the preparatory treatment of body external surfaces for the enamel finish painting. To this end, the bodies are first cleaned and sanded, then dried in oven. Next, the bodies move on and pass through two paint booths equipped with specially designed "silhouettes" surrounding the bodies to create the around same an area of pressures higher than normal booth environmental pressure: this is obtained by repeatedly pumping filtered air. The paint spray guns operate on filtered compressed air. In the first 24-meter long booth the paintwork is applied to body internal surfaces and a first enamel coat is deposited on exterior surfaces. In the second 12.5 meter long booth the second coat of enamel is sprayed on.
The GT paint range covers 9 different colors, of which 4 are metalized finishes. After the application of the finish coat, the bodies are conveyed through a 140 degree Celsius paint baking line oven. On the terminal end of this line a 100 percent inspection is carried out on all bodies; any flaw will be corrected by suitable touch-up operations.
The bodies which pass the extremely severe paint inspection stations are moved on to the final trimming and assembly lines. On entering the line, the body is tagged with a data processing card giving all the necessary details on the type of trim chosen by the buyer.
Due account being taken of the color range, various trim and equipment versions, as far as Brissoneau & Lotz are concerned the GT may be produced in 740 different combinations. Along this line, at present producing 85 completely finished and trimmed bodies daily, more than 800 odd parts are fitted.
Sub-assembled in specially provided bays along the main assembly line are some of the equipment for the fuel tank, instrument panel, windshield wipers, rear bumpers, etc. (including the windshield and back window weatherstrips), all of which will be installed later on the body.
Worthy of note is that all the electrical system wiring and harnesses for the GTs trimmed at Creil are produced in a special Brissonneau & Lotz shop. Also the seats trimmed at Creil in an upholstery shop where about 250 people handle the cutting to size and installation of foams and imitation leather coverings intended for the seats and interior trimming (headlinings, door inner panels, windshield pillar trims, etc). 20 percent of the parts fitted on the bodies comes from supply sources abroad. All the operations performed along this trimming and finishing line are systematically checked by specially trained inspectors.
Utmost care is therefore devoted to the installation of the so-called "safety items." At the end of the line a 100 percent inspection is made of the entire electric system. Next is the "rain" test to check all bodies for absolute water tightness. At this stage a point-by-point inspection of the complete bodies is performed by the Quality Control men who check all the essential components, one by one. If the result is satisfactory, the bodies are ready for sale but before shipment they are submitted to a last painstaking check for conformity to safety standards, the United States Motor Vehicle Safety Standards in particular.
All bodies which pass this severe inspection schedule and the numerous spot checks along the line are shipped to Bochum, Germany, where they will receive their mechanical components. Carried on specially designed dollies the bodies are loaded onto the wagons of trains that transport 85 units per day. Also shipped are the trimming components (80 sets daily) intended for the completion of bodies at Bochum to meet the ever increasing demand for GTs on the international market.
The commencement of the production series, slated for September 1968, was respected as a date in spite of the known May labor troubles in France and the technical problems raised by some complex body components.
At the onset of 1969, the daily output had already reached the 80 units rate. The importance of the rigorous checks performed systematically on the parts coming from external supply sources as well as along the flow lines of the production process cannot be overemphasized.