The Apex of full-sized Mercedes coupés.
During the 1970s, when the engineers at Daimler-Benz’s Sindelfingen nerve centre were in the driving seat, Mercedes could be relied upon to do things properly. For if their cars were mostly on the large side – often somewhat heavy-jowled – they were mostly fit for their purpose, whether intended for the commercial trades, for plutocratic conveyance, or simply chariots of the indulgent.
Research and development was key to the three pointed star’s pre-eminence. Mercedes engineers not only worked through what ever technical challenge they were attempting to overcome, but also considered all of the alternatives – frequently going so far as to build an exhaustive array of prototypes to eliminate from their deliberations the merely plausible.
The 126 series was the result of one such engineering research programme, initiated in 1971, and gaining particular impetus following the shock to the ecosystem that followed the 1973 oil embargo. In its aftermath the watchword at Stuttgart Untertürkheim became one of efficiency. If the once intemperate luxury car was to survive into the following decade, it was going to have to study frugality, cleave the air in a less restrictive fashion and jettison those corpulent excess kilogrammes.
But a more compact car was out of the question for a host of reasons, as outlined to journalists in 1979 by head of development, Friedrich van Winsen, not least the fact that Mercedes’ customer data at the time illustrated that S-Class customers covered twice the annual mileage of the average German, while conveying a greater number of passengers. No, smaller was not a viable option; the answer had to lie with a more intelligently engineered car.
The W126 programme would achieve fruition in Autumn 1979 with the debut of the second-generation S-Class. To those established qualities of active and passive safety, user convenience and driver-focus, Mercedes’ engineering team, overseen by Professor Werner Breitschwerdt, melded those principles of efficiency and social responsibility which so defined its genesis. Much as intended, the W126, in true Sindelfingen fashion, reset the luxury saloon benchmark, just as its W116 predecessor had done seven years earlier.
Mercedes-Benz outlined the W126 concept to the world’s press in typically understated terms: “to further improve in a sensible manner those features which had characterised all previous top-class Mercedes cars; a maximum of comfort and performance, based on the latest findings in engineering, safety and reliability, complemented by a level of quality in manufacture and styling that sets the standards“.
Continuity, while simultaneously embracing radical change was very much the order of play when it came to the 1979 Sonderklasse, but for its more indulgent two-door equivalent, a slightly different set of priorities would come to the fore. Its direct predecessor, the C107 SLC series, had been based on the equivalent SL; and while the outgoing SLC had its proponents, it was something of an anomaly in Untertürkheim terms, being the first, and as it would prove, only example of a full-sized Mercedes coupé to be twinned with the more sporting SL line.
Even if it looked a good deal lighter on its feet than its forebears – or indeed its successor for that matter – the 1971 SLC was no lightweight. But despite healthy sales over its lifespan, the Mercedes supervisory board concluded that this approach was no longer the preferred direction of travel. The C-126 therefore would mark a return to business as usual, closer to the highly regarded W111 coupés of yore in scale and ‘presence’.
By consequence, and for sound cost and marketing reasons, the SEC was twinned with W126, both in engineering and stylistic terms. Sharing running gear and technical hardware with the saloon, the C126’s bodyshell employed a short-wheelbase (3″ less) version of the saloon floorpan. A coupé in the dictionary sense of the word, its roofline was an inch lower, for a more rakish profile. To save weight, aluminium was employed to skin the bonnet, boot lid and rear bulkhead.
Having ascended to the design leader role, the W126/C126 programme was to mark the first model line to be wholly overseen by Bruno Sacco; his brief being to reflect the styling of the saloon, but to subtly shift the emphasis from stiff formality towards something at least approaching a more relaxed demeanour. Central to this was the nose treatment – for the first time on a full-size Mercedes coupé, a horizontal grille motif would reflect that of the SL model line rather than the more formal, vertical arrangement which had been the norm.
In terms of surfacing and overall body architecture, the SEC cleaved closely to the W126, but the second and most profound departure lay in the treatment of the canopy. The lower roofline lent the silhouette an element of almost Italianate grace, culminating in the beautiful sweep of the C-pillar towards the rear deck line. Like all Mercedes coupés, there was a pillarless arrangement to the side glazing, the glass retracting to create an seamless, unimpeded opening. Elegance reigned.
In the arrangement of the car’s volumes, forms and intersections, the SEC was a masterclass. But there was science too behind the beauty. The SEC’s coefficient of drag was 7 % lower than that of its W126 saloon stablemate; its Cd at 0.34 an improvement of 15% over its SLC forebear (which appeared lower slung) while its CdA was 7% less.
The cabin was also derived from that of the saloon, the dashboard and instrument panel being shared and identical in layout. The seats however were of a different, more enveloping design with increased side bolstering. The rear seats too were of the individual type. A neat touch was an arm which extended to offer the seatbelt to front seat occupants as soon as they key was inserted into the ignition. Typical Mercedes insofar as this could be termed as both a safety and convenience feature. Otherwise, all was as logically laid out and superbly assembled from quality materials as any Daimler-Benz product of the era.
While most of its technical hardware was shared with the saloon, the SEC marked the debut of Mercedes ‘Energy Concept’ series of V8 engines. Based upon the existing power units, the two V8s offered were essentially redesigned, the 3.8 litre employing a longer stroke length, and a lower compression ratio, providing more torque at lower crankshaft speeds, improving driveability and economy, especially in its high-geared top ratio. This was no idle boast either. In a July 1982 test report, Autocar described the economy figures obtained from their subject 380 SEC as being “outstandingly good”.
The W126’s road behaviour was lauded by all who drove it for the thoroughness of Mercedes’ chassis engineering and the car’s imperious capabilities in all road conditions. The SEC further improved upon this, motor journalists citing the coupé’s improved steering response, more surefooted handling and of course its superb braking capability, bolstered considerably by the (highly desirable) option of the Bosch ABS anti-lock system.
During this period, the major European carmakers maintained something of an unofficial non-compete agreement, where the likes of Mercedes, BMW and Jaguar agreed not tread upon one another’s toes, instead playing to their respective marque-specific qualities. But even allowing for this, and acknowledging that the SEC played very much to Mercedes’ core strengths, the big Swabian coupé, like its saloon sibling existed very much in a class of one. While others such as Porsche or BMW might have fielded cars which nipped at the SEC’s heels, none could really offer anything close to the sheer breadth of talent the big Mercedes coupé embodied.
Just over 73,000 SECs were built over a ten year production run, the final example leaving Sindelfingen’s tracks in August 1991. The C140 that replaced it was a fine car, but one that suffered to a certain extent from the same excess of ambition and mission creep that afflicted its saloon donor, and while there have been S-Class coupés of various stripes on sale up to 2021, none of the generations that followed came close to the essential rightness, patrician grace, calm and sheer rigor of the SEC.
Some stars just shine that much brighter.
 Bruno Sacco: “Of all the Mercedes-Benz models I was responsible for designing, the C 126 has the most beautiful front end.”
 With the possible exception of the front wings (fenders), it is unlikely that a single external pressing was shared with the W126 saloon.
 Amongst the styling studies for C126, was one whose C-pillar and rear screen treatment reflected that of the W111 Coupé from the 1960s. While elegant, it’s clear Sacco and the Mercedes Supervisory board made the correct choice.
 The distinctive external door handles were cleverly designed to resist road grime, but looked unsightly. Sacco and his design team loathed them, but Engineering would not be moved.
 The eminent Italian former design chief retains a 1989 560 SEC in his personal garage.
 In its 1981 Car review, it stated, “There is no on-board computer, and Daimler-Benz say, there won’t be one. Mercedes’ owners, they say, want to drive their cars, not play games with them“. Oh, has the world changed or have I changed?
 The SEC was only available with Mercedes’ own 4-speed automatic transmission. There was no manual option.
 Initially, US market SECs were only offered in 380 form to comply with CAFE restrictions. With full emissions equipment it was no ball of fire. This was remedied in 1984, with the introduction of the 5ooSEC.
 This was retained by the Daimler Museum.
 The S-Class coupé is no more, the C222 being the final iteration of the line.
 The combination of Prof. Werner Breitschwerdt in Research & Development and Bruno Sacco in design was to prove an unsurpassed combination of talents at Sindelfingen. So much so that few to this day can quite grasp just how far ahead of their rivals Mercedes were at this time. Tellingly, Mercedes-Benz’s current styling imperator has since derided Sacco’s work, the stable genius of Carlsbad describing it as “forced”. This is wrong on so many levels that it’s almost laughable – not least that the correct usage of the term suggests an involuntary act – which in Sacco’s case may well have been the case. After all, Sacco couldn’t help being gifted, just as his Gordenness can’t help being distinctly mediocre.
For 1986, both W126 and C126 received a minor cosmetic facelift, while for the SEC, engine capacities encompassed 420, 500 (in some markets) and 560 designations.
In 1983, Breitschwerdt became Chairman of the Board of Management of Daimler-Benz AG, a position he was ousted from in 1987, much to Mercedes-Benz’s detriment.
Sources: Car magazine – December 1979/ Autocar – 17 July 1982/ Car magazine – December 1981/ Mercedes-Benz.com