I. Defending the Throne
By the late 1980s, Mercedes-Benz had little to prove. The W126 S-Class was the standard. No rival matched its presence, durability, or numbers. The idea that Stuttgart could be blindsided seemed far-fetched—until BMW changed everything.
BMW’s E32 7 Series arrived in 1986. A year later, the 750iL dropped: Germany’s first postwar V12 sedan, and a shot straight at Stuttgart. The effect was immediate and deeply personal. The head of Mercedes-Benz was furious—caught flat-footed by Munich’s boldness, and by how much ground BMW covered in a single move.
Mercedes, with the W140’s development nearing completion, went into crisis mode. Deadlines were pushed back a year or more. Mercedes delayed its new S-Class by nearly two years, pushing a 1989 debut all the way to 1991. The reason was clear: Stuttgart refused to show up without an answer to BMW’s Zwölfzylinder. The response was all-hands: an all-new 6.0-liter M120 V12, plus hasty reengineering of nearly every major system. The cost ballooned past 1.5 billion Deutsche Marks. Frustrations mounted. The chief architect was forced out before the car even launched.
The consequences were real. Instead of launching in 1989—alongside the Lexus LS400, whose design practically whispered corporate espionage—the new S-Class arrived five years after the E32 and four years after the 750iL. For Mercedes dealers, it was agonizing to watch rival innovations pass them by: Toyota’s obsessive refinement, BMW’s headline-grabbing technology, Jaguar’s XJ40, even incremental advances from Cadillac and Lincoln. The S-Class had always been the future; now, for the first time, it was playing catch-up.
But the brief had only subtly changed: retake the crown instead of just keeping it. By late 1987, the design was locked. When the W140 debuted in 1991, it was heavier, more complex, and more expensive than any Mercedes before it—engineered to make even Munich’s breakthrough feel like old news.
Some of the wildest ideas didn’t survive prototype testing. Mercedes engineers experimented with a “dual chassis” design: a secondary internal frame isolating the passenger cabin from the primary structure, inspired by coachbuilt limousines that once used leather straps to float the body. For 18 months, the team pursued the concept, but it proved too complex to realize in time. Still, the ambition spoke volumes.
So did the engine experiments. Rumors that BMW was testing a V16 “Goldfisch” prompted Mercedes to develop its own 7.3-liter V16, essentially an elongated M120 producing over 550 hp. As many as 85 test mules were reportedly built. Even more radical was the proposed M216 W18, a compact 8.0-liter engine with three banks of six cylinders arranged in a 75-degree triangular “W” layout. It was designed to produce 490 hp in standard form, with a mooted 680 hp performance variant. Thanks to its geometry, it would have been no longer than a conventional inline-six. But after what amounted to a de facto disarmament treaty with BMW, both engines were quietly shelved. They were destined for the history books as figments of the two makes’ cylinder Cold War. Their existence nonetheless underscored how uncompromising the W140’s engineering brief truly was.
Early sketches featured a lower roofline and a sportier stance – essentially a “Germanic Jaguar.” However, this vision was soon compromised by an ergonomic mandate: the car had to comfortably accommodate two 6′3″ adults sitting one behind the other (even wearing hats). Mercedes board members (chief engineer Wolfgang Peter and program manager Rudolf Hornig) sat in a full-size interior mockup and both promptly bumped their heads on the headliner.
In response, the development team raised the roof by about 50 mm (2 inches), despite Sacco’s protests that it made the car look “top-hatted” . Mercedes-Benz boss Werner Niefer sided with the engineers, prioritizing headroom over styling. This seemingly small change cascaded into bigger issues: the taller profile upset the handling balance, so the entire car was widened to compensate.
The final car was big, but not as outsized as legend suggests. The short-wheelbase W140 measured 5.11 meters (201.38 inches). The long-wheelbase version stretched to 5.21 meters (205.24 inches), just five centimeters longer than the outgoing W126 560 SEL at 5.16 meters (203.15 inches). The real difference was in mass and stance. The W140 was taller, wider, and visually denser, with curb weight ranging from 4,167 lb for the 300 SE to 4,828 lb for the 600 SEL. This was several hundred pounds heavier than its predecessor. For context, the contemporary BMW 750iL (E32) was in another size class altogether. It measured just 5.01 meters (197.24 inches) in length and sat noticeably lower.
He even considered exaggerating the verticality with an ultra-tall glasshouse before abandoning the idea. In Sacco’s words, the production W140 looked better suited to “monarchs and dictators on parade” than the dynamic express he had once envisioned. But Mercedes pressed forward, convinced that technical supremacy would override stylistic dissent.
The W140 finally debuted at the March 1991 Geneva Motor Show, unveiled in dramatic fashion. A giant wooden crate was lifted from the stage to reveal the car, underscoring its scale, presence, and gravity. Mercedes had spent nearly a decade and a fortune developing its new Sonderklasse. But one question remained. Had they created the greatest luxury car in the world, or a monument to excess, arriving just as the world began to turn? Could it be both?
The flagship engine was the new M120 6.0-liter V12, Mercedes’ first production V12 and a technical showpiece. All aluminum, it delivered 408 hp and 580 Nm, vaulting the 600 SEL well past the BMW 750iL’s 300 hp. The M120 was engineered for both refinement and longevity, with a 60-degree vee, quad cams, four valves per cylinder, sequential injection, and full electronic ignition. Its modular layout shared architecture with the new V8s and sixes. The W140 lineup also included a 4.2-liter V8 (286 hp), 5.0-liter V8 (320 hp), and a 3.5-liter inline-six diesel, all with four-valve heads and modern management. Variable intake cam timing was standard on all gasoline engines, a first for the S-Class. From 1992, a 2.8-liter 24-valve inline-six (193 hp) filled out the range. V12 and V8 models launched with a 4-speed automatic, while six-cylinders offered a 5-speed manual or auto. An upgraded 5-speed automatic with locking torque converter replaced the older unit on V8s in 1996, improving both acceleration and fuel economy.
Chassis technology was equally advanced. Up front, a new double-wishbone suspension replaced the W126’s simpler setup. In the rear, Mercedes used its proven multi-link independent suspension, refined from the W201 and W124. Ride quality was elevated by the optional Adaptive Damping System (ADS), an electronically controlled hydropneumatic suspension that actively varied damping in real time using “skyhook” logic. ADS came standard on V12s and optional on V8s, and later included rear load-leveling. The result was uncanny composure—magic-carpet smooth yet surprisingly agile. Auto Motor und Sport called the W140’s suspension “outstanding” and the handling “amazingly nimble for a car of this size and weight.” The dynamics defied its mass.
Mercedes went to obsessive lengths to make the W140 the quietest, most refined car on the road. It was the first production car with double-pane insulating glass in every side window. This twin-pane glass all but erased wind and road noise, eliminated fogging, and improved thermal insulation. Autobahn travel at 200 km/h was whisper-quiet; at 130 km/h, as one journalist noted, “passengers hear nothing. Absolutely nothing.” Silence was enforced by flush windows, triple door seals, optimized wipers, and over 30 distinct insulation measures, from firewall padding to acoustic foams in body cavities. Body panels were double-layer galvanized steel, built for decades of use. Even the car’s weight was deliberate. Jürgen Hubbert, head of Mercedes-Benz passenger cars, said, “The weight is the price to be paid for the comfort the car offers.” Mass itself became an insulator, pushing Mercedes’ old philosophy to its absolute limit.
The W140 was one of the first cars with a networked electronic architecture, debuting a multi-node CAN (Controller Area Network) bus linking major control systems. Five separate modules—engine, transmission, chassis, body, instrumentation—communicated over shared data lines, eliminating redundant wiring and allowing subsystems to work in concert. Climate control, for example, could seamlessly raise idle speed when the air conditioning compressor engaged, all coordinated electronically. This was cutting-edge in the early 1990s and set the pattern for modern automotive electronics.
The car introduced a suite of new electronic features. Memory systems stored not just seat positions, but steering column and mirror settings as well. Power-folding mirrors were standard. Automatic rain-sensing wipers debuted, using a windshield sensor to detect moisture. The climate control was fully automatic with dual zones, and four-zone available on long-wheelbase models, even running after engine-off to maintain cabin temperature.
One particularly memorable feature was the dual rear parking guides. Early W140s had thin guide rods that rose from the rear fenders when reverse was engaged, giving the driver a visual reference for the car’s far corners. In 1995, these were replaced by the industry’s first ultrasonic Parktronic system—sensors in the bumper, beeping faster as you neared an obstacle. That same year, the S600 Coupé for Japan introduced a GPS navigation system with a color screen and CD-ROM mapping, making the W140 one of the first production cars with factory nav. Linguatronic voice control followed in 1996 for phone and audio functions. TeleAid, an early telematics and emergency call system, appeared in the U.S. in 1997, paving the way for GM’s OnStar.
The W140 was also the first car in the world with a yaw-based Electronic Stability Program (ESP), co-developed with Bosch. ESP arrived on the 1995 S600 Coupé, then spread across the range. It could brake individual wheels and cut engine power to prevent a skid. Brake Assist (BAS) debuted in 1996, detecting emergency braking and instantly applying full pressure. Today, both systems are mandatory almost everywhere.
Passive safety was just as advanced. All W140s came with dual airbags and ABS. From 1996, door-mounted side airbags became available up front. Seat occupancy sensors could disable the passenger airbag for an empty or child seat. Pretensioners and load limiters were standard on the front belts. Mercedes tested the W140 in simulated and real crashes, even crashing it into the lighter W126 to make sure the new car’s mass wouldn’t turn it into a battering ram. Engineers tuned the crumple zones to deform more gently in low-speed collisions with smaller cars.
The W140 was saturated with innovation, a reflection of Mercedes’ engineer-driven mindset at its zenith. Comfort, performance, safety—every system was the best that could be done, with no regard for compromise.