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. Mercedes-Benz was caught flat-footed by Munich’s boldness, and by how much ground BMW covered in a single move.
With the W140’s development nearly finished, Stuttgart abruptly shifted into crisis mode. Deadlines slipped by a year or more, and the planned 1989 debut was pushed all the way to 1991. The reason was obvious: Mercedes refused to arrive without a direct counter to BMW’s Zwölfzylinder. The scramble was total, with an all-new 6.0-liter M120 V12 and rapid reengineering of almost every major system. Costs surged past 1.5 billion Deutsche Marks.
The consequences were immediate. Instead of launching in 1989 alongside the Lexus LS400, whose design hinted at corporate espionage, the new S-Class appeared five years after the E32 and four years after the 750iL. For Mercedes dealers, it was painful to watch rival innovations pass them by: Toyota’s obsessive refinement, BMW’s headline-grabbing technology, Jaguar’s XJ40, and even incremental advances from Cadillac and Lincoln. The S-Class had always been the future. For the first time, it was playing catch-up.
The brief had shifted only slightly. The goal was now to retake the crown, not simply defend 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. It was built to make Munich’s breakthrough feel like old news.
Some of the wildest ideas never made it past prototype testing. Engineers tried a “dual chassis” design, with a secondary frame to isolate the passenger cabin from the main structure. The concept was inspired by old coachbuilt limousines that floated their bodies on leather straps. After 18 months of development, it proved too complex to finish. The ambition was clear.
The engine experiments were just as ambitious. Rumors of a BMW V16 “Goldfisch” spurred Mercedes to create its own 7.3-liter V16, an elongated M120 with more than 550 horsepower. As many as 85 test mules were built. Even more radical was the unbuilt M216 W18, a compact 8.0-liter with three banks of six cylinders in a 75-degree triangular layout. It was designed for 490 horsepower in standard form and 680 in a performance variant. The size matched a conventional inline-six. After what was essentially a disarmament pact with BMW, both engines were shelved. They became relics of a cylinder-count Cold War, proof of how uncompromising the W140’s engineering brief had been.
Early sketches had a lower roofline and a sportier stance, essentially a “Germanic Jaguar.” That ended when chief engineer Wolfgang Peter and program manager Rudolf Hornig tried a full-size mockup and both bumped their heads. Someone forgot to tell them that Jaguars, like Rolls-Royces and Bentleys, were known for tight quarters. The car now had to fit two adults six-foot-three, one behind the other, without compromise.
The team raised the roof by 50 millimeters, despite Bruno Sacco’s protests that it made the car look “top-hatted.” Mercedes-Benz boss Werner Niefer sided with the engineers, choosing headroom over styling. The taller profile upset the handling balance, and the entire car was widened to compensate.
The final car was big, though not as oversized as legend suggests. The short-wheelbase W140 measured 5.11 meters, and the long-wheelbase 5.21 meters, only five centimeters longer than the outgoing W126 560 SEL. The real difference was in mass and stance. It was taller, wider, and visually denser, with curb weights from 4,167 pounds for the 300 SE to 4,828 pounds for the 600 SEL, several hundred more than its predecessor. By comparison, the contemporary BMW 750iL was a size class smaller at 5.01 meters and sat noticeably lower.
He even considered exaggerating the height with an ultra-tall glasshouse before abandoning the idea. Sacco later said the production W140 looked better suited to “monarchs and dictators on parade” than the dynamic express he had envisioned. Mercedes pressed on, confident that technical supremacy would outweigh stylistic dissent.
The W140 debuted at the March 1991 Geneva Motor Show in dramatic fashion. A giant wooden crate was lifted from the stage to reveal the car, emphasizing its scale and presence. Mercedes had spent nearly a decade and a fortune on the new Sonderklasse. Had they built the greatest luxury car in the world, or a monument to excess 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. Built entirely from aluminum, it produced 408 hp and 580 Nm, putting the 600 SEL well ahead of the BMW 750iL’s 300 hp. Designed for both refinement and longevity, it had 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 range also included a 4.2-liter V8 with 286 hp, a 5.0-liter V8 with 320, and a 3.5-liter inline-six diesel. Variable intake cam timing and four-valve heads were standard on all gasoline engines, a first for the S-Class. From 1992, a 2.8-liter 24-valve inline-six with 193 hp joined the lineup. V12 and V8 models launched with a four-speed automatic, while six-cylinders offered a five-speed manual or automatic. An upgraded five-speed automatic with locking torque converter arrived for V8s in 1996, improving both performance and economy.
Chassis technology was equally advanced. A new double-wishbone front suspension replaced the W126’s simpler setup, while the rear kept Mercedes’ proven multi-link design from the W201 and W124. Ride quality improved further with the optional Adaptive Damping System (ADS), an electronically controlled hydropneumatic setup that varied damping in real time using “skyhook” logic. ADS was standard on V12s, optional on V8s, and later added rear load-leveling. The result was uncanny composure, smooth like a magic carpet yet surprisingly agile. Auto Motor und Sport called the 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, eliminating wind and road noise, preventing fogging, and improving thermal insulation. At 200 km/h on the autobahn it was whisper-quiet. At 130 km/h, as one journalist noted, “passengers hear nothing. Absolutely nothing.” Silence came from flush windows, triple door seals, optimized wipers, and more than 30 separate insulation measures, from firewall padding to acoustic foams in body cavities. Body panels were double-layer galvanized steel, built to last decades. Even the 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, taking Mercedes’ old philosophy to its absolute limit.
The W140 was among the first cars with a networked electronic architecture, debuting a multi-node CAN (Controller Area Network) bus that linked major control systems. Five separate modules for the engine, transmission, chassis, body, and instrumentation communicated over shared data lines, which eliminated redundant wiring and let subsystems work together. Climate control, for example, could raise idle speed when the air conditioning compressor engaged, all managed electronically. This was cutting-edge in the early 1990s and set the pattern for modern automotive electronics.
The W140 introduced a suite of new electronic features. Memory systems stored not only seat positions but also steering column and mirror settings. Power-folding mirrors were standard. Automatic rain-sensing wipers made their debut, using a windshield sensor to detect moisture. The climate control was fully automatic with dual zones, with four-zone available on long-wheelbase models, and could continue running after the engine was switched off to maintain cabin temperature.
One 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, with bumper-mounted sensors that beeped 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 navigation. 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 the first car in the world with a yaw-based Electronic Stability Program (ESP), co-developed with Bosch. ESP debuted on the 1995 S600 Coupe and then spread across the range. It could brake individual wheels and cut engine power to prevent a skid. Brake Assist (BAS) followed in 1996, detecting emergency braking and instantly applying full pressure. Both systems are now mandatory in most markets.
Passive safety was equally advanced. All W140s came with dual airbags and ABS. From 1996, door-mounted side airbags were 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 both simulated and real crashes, even ramming it into the lighter W126 to ensure its mass would not turn it into a battering ram. Crumple zones were tuned to deform more gently in low-speed impacts 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.