Mercedes-Benz S-Class, W 140 series (1991 to 1998)

In March 1991 the new S-Class generation (W 140 series) made its debut at the Geneva Motor Show. The body design incorporated the typical traditional Mercedes-Benz stylistic elements and thus fitted unobtrusively into the homogenous design of the passenger car model series. As had already been the case with the SL models in the R 129 series, with the new S-Class the distinctive trademark radiator grille was given a new stylistic interpretation while retaining the traditional basic shape. This variation on a classic theme was designated the “integrated radiator” and with its much narrower chrome frame the radiator shell was organically integrated into the engine lid. For the first time, the Mercedes star was positioned not on top of the radiator grille, but slightly to the rear on the engine hood. The overall aim of the design concept of the new S-Class generation was to achieve a high degree of aerodynamic quality while at the same time respecting a maximum of everyday practicality.
As with the predecessor models of the W 126 series and generations of Mercedes-Benz premium-class series before them, the normal version was also accompanied by a long-wheelbase variant, in which the additional 100 millimetres served exclusively to increase legroom in the rear. As far as the engine was concerned, initially four units were available on the domestic market, of which only the 5.0-liter V8 four-valve M 119 was an old and familiar friend. As with the 500 E of the mid-range W 124 series, the engine used here was the so-called Einheitsdeckmotor (standard engine) – a crankcase for both the 4.2 and 5.0-litre assemblies – whose fully-electronic Bosch “LH Jetronic” injection system was controlled via a hot-wire air mass sensor. The other three engines were newly developed: Like the 5.0-liter unit, the 4.2-liter four-valve V8 was based on the 4.2-liter two-valve engine, and the six-cylinder in-line engine with 3.2-liter displacement was based on the 3.0-liter four-valve unit introduced two years earlier. An interesting detail to note here is that the model designation of the 3.2-liter and 4.2-liter models did not reflect exactly the displacement as had always been the case in the past. Instead, for the sake of homogeneity the designations 300 SE/SEL and 400 SE/SEL were chosen.
The twelve-cylinder
The 6.0-liter V12 M 120 engine was an entirely new design, not just the first series-produced twelve-cylinder Mercedes-Benz passenger car, but also the most powerful Mercedes-Benz car engine of its day, with a rated power output of 300 kW (408 hp). With a peak torque of 580 Newton metres, it reached the 500 Newton metres mark at 1600/min. As with the six-cylinder and the two V8 engines, the twelve-cylinder was also equipped with four-valve technology, variable intake camshaft and an electronic injection system with hot-wire air mass sensor. With all engines a high priority was placed on minimizing exhaust emissions and reducing fuel consumption. The new fully electronic ignition system calculated the optimum ignition point from 300 ignition maps, tuned for each cylinder individually and to the knock limit in each case. The M 120 was the only twelve-cylinder engine worldwide to feature this cylinder-selective anti-knock control. This alone made possible the high compression ratio of 10:1, necessary for optimum use of fuel.
Engine and drive management was also completely new. Here, all control modules communicated with one another via a common data channel, which meant that the control units were jointly active. This served for rapidly warming up the catalytic converters on cold-starting the engine, for example, as well as for acceleration skid control ASR and for the new engine friction torque control, which maintained handling stability during power-off situations on slippery road surfaces.
The V12 offered the world’s largest catalytic converter unit for passenger cars. With a seven-litre volume in order to avoid any excess fuel consumption on account of the catalytic converter, it ensured a high degree of long-term stability. Thanks to an innovative concept involving a double-walled and triple-insulated exhaust manifold, as well as double-walled pipes, the ceramic catalytic converters – embedded in insulating expandable matting – reached the optimum operating temperature in a very short time.
Environmental compatibility
In addition to optimizing and reducing exhaust emissions, the W 140 series also featured a number of other details that made it a pioneer for environmentally compatible automotive production. It heralded the age of the CFC-free (chlorofluorocarbons) car and set new standards in terms of recycling. The plastic components used were not only recyclable and clearly identifiable, they were also to a large extent manufactured using regranulated plastics. In 1992 the W 140 series won an environmental award from the US Environmental Protection Agency, the “Stratospheric Ozone Protection Award.”
Apart from reducing fuel consumption and optimizing environmental compatibility, development of the W 140 series placed a special emphasis on raising comfort and safety to new levels of perfection. In this respect, the meticulous design and coordination of the running gear played a particular role. A newly developed double wishbone front axle, with the main point of load application mounted on a subframe, provided front suspension – a system designed to isolate the body from audible and perceptible vibrations. Rear suspension was derived from the multi-link independent suspension of the other passenger car series, although radically revised in terms of wheel location and modified in line with the special requirements of the
S-Class. To take account of the significantly greater longitudinal and transverse forces, the link geometry was also redesigned. Of particular interest was the crossed design of the upper links, which allowed axle space to be kept to a minimum in spite of the long control arms.
In terms of active safety the S-Class saloons in the W 140 series were known for their exceptionally good straight-line stability even on uneven road surfaces, their low crosswind sensitivity, precise and responsive steering and handling which remained relatively unaffected by the size of payload. The brake system for the eight and twelve-cylinder models was a fundamental innovation. By distributing more braking power to the rear wheels, it was possible to improve the fade resistance of the brake system and reduce wear to the front wheel brakes.
High degree of ride comfort
Ride comfort in the W 140 series was improved significantly once again. Any tyre noise and vibrations transmitted to the passenger cell were largely reduced, the pitching motion on moving off and braking was minimized, rolling motion on cornering or uneven road surfaces was reduced and the steering was made virtually insensitive to jolts transmitted from the road. A so-called “parameter steering” with speed-sensitive steering moment was fitted as standard to the eight and twelve-cylinder variants, reducing the steering effort required by the driver at low speeds, for example when parking.
Safety had already been taken to high standards in the predecessor model series, but here numerous measures achieved further improvements. The new body structure, for example, provided even more safety in all types of accidents. And a series of small design appointments designed to reduce hazards from potential impact points also gave added protection to other road users.
The first soundproofed glass windows to be fitted to a passenger car series also made a significant contribution to improving comfort and incorporated a range of safety and comfort features. They avoided the tendency to fog or ice up and reduced condensation, gave better heat insulation as well as soundproofing from external noise, improved external air flow and eliminated wind noise caused by window seals.
Two further design details – folding exterior mirrors and extendable guide rods to help with reversing – gave drivers additional assistance when manoeuvring in small spaces with poor visibility. The electrically-operated exterior mirrors could be folded back to gain extra space when manoeuvring in tight situations by means of a centrally-positioned switch on the centre console, the same switch serving also to angle the mirrors correctly. In order to assist with judging distances to obstacles when performing reversing manoeuvres, two extendable guide rods were integrated into the rear fenders to left and right. Two seconds after selecting reverse gear, the pneumatically operated 65-millimeter-long chrome rods automatically extended vertically, returning again eight seconds after a new gear had been selected.
Diesel for Europe
At the Paris Motor Show in October 1992, the 300 SE 2.8 and 300 SD Turbodiesel models were introduced, adding two cheaper and particularly economical variants to the S-Class range. The 300 SD attracted particular attention – a vehicle that had been exported to the USA since October 1991, but which was now the first diesel model in the S-Class to become available in Europe. The 300 SD was powered by a 3.5-liter six-cylinder engine with exhaust-gas turbocharger, a unit which was in principle the same as the one used in the predecessor model from the W 126 series, but now in a revised version delivering 110 kW (150 hp). Like the 300 SE, the second new arrival, the 300 SE 2.8, offered a six-cylinder in-line unit with four-valve technology – also a member of the M 104 family of engines. The newly developed 2.8 litre variant was used from the same point in time in the W 124 series also and was equipped with a microprocessor-controlled direct injection system in which the hot-wire air mass sensor had been replaced by a hot-film air flow sensor. In addition to the two new models, the eight and twelve-cylinder versions appeared in Paris with revised engines. All three units did away with mixture enrichment under full load, resulting in a minor loss of output but bringing benefits in terms of emissions.
In June 1993 the model designations were changed to come in line with other series in the passenger car range; the “S” was now placed before the three-figure number, and suffixes such as “E”, “D” and “L” were omitted. The 500 SE, for example, became the S 500, and according to the new system of nomenclature the 600 SEL was renamed the S 600 long. Ever since, the trunk lid has documented only the class and engine displacement and not the body variant (normal or long-wheelbase version) – this was entirely apparent to anyone taking a closer look. The most significant changes came in redesignating the 4.2-liter and six-cylinder models. Instead of the figures used hitherto, which had been rounded off to full hundreds in order to enhance the uniformity of the overall image, the figures used corresponded to the actual displacement values. Thus the 300 SE for example became the S 320 and the 300 SD was now known as the S 350 Turbodiesel. In addition to these purely formal changes, the two 3.2-liter models also benefited from a number of technical improvements. The previously used engine was replaced with a revised version that had already been in service since October 1992 in the W 124 mid-range series and now also featured a variable-resonance intake manifold and a direct injection system with hot-film air flow sensor. These improvements permitted an increase in torque and meant both maximum output and maximum torque could be achieved at lower engine speeds. Thanks also to an additional reduction in friction losses, fuel consumption was reduced by a total of 7.5 percent and overall performance marginally improved.
Discreet revisions
At the Geneva Motor Show of March 1994 the S-Class saloons were presented with discreet stylistic modifications. A series of modified details gave the optical illusion of a lighter, better proportioned and more dynamic appearance – even though external dimensions remained unchanged. This was achieved by a distinctive “tucking-in” of the lower parts of the bumpers and side skirts and by the horizontal subdivision of these surfaces by means of a beading running all the way round. The effect was reinforced by modifying the design of the headlamps and radiator protection grille. In the modified headlamps with optimized variable-focus reflectors, which increased light output by 60 percent, the dipped-beam compartment was no longer separated by a central bar from the high-beam compartment, thus lending the illusion of greater breadth. This impression was underlined by the addition of colourless glass covers for the front turn indicator lamps. The six and eight-cylinder models were also given a newly designed, more slender radiator grille with a vertical articulation at the centre. For the V12 models there was also a special version with chrome-plated transverse fins and appreciably broader chrome frame. Formal modifications to the rear end were also a significant factor in the harmonious overall image of the S-Class. For example, the lower radii of the trunk lid joints were rounded off in the same style as the coupe models. The taillight band was made broader beneath the rear lamps and shaped to fit the new bi-chromatic design of the rear lights. This served to flatten off the height of the trunk and to make the rear end as a whole appear broader and lower set.
From May 1995 the ultrasonic reversing aid PARKTRONIC was available as an option. Ultrasonic signals emitted by the system were reflected by any obstacle encountered and the distance between vehicle and obstacle was then calculated by an electronic control unit. Transmitters and receivers of the ultrasonic signals were combined in sensors integrated into front and rear bumpers, without diminishing in any way the protective function of the bumpers. PARKTRONIC was fitted as standard equipment to the V12 models from 1995 onwards. At the same time, the now superfluous guide rods in the rear fenders were discontinued in all S-Class limousines.
Improved engines
Since the model refinement measures introduced in 1994 essentially affected design, the eight and twelve-cylinder models saw a number of technical improvements in September 1995. A completely new five-speed automatic transmission with torque converter lock-up clutch – a unit that had been fitted to the S 600 coupe since May 1995 – now replaced the four-speed transmission with hydraulic control in the saloons. At the heart of this technological miracle was an electronic transmission control unit which adapted gear-shifting rapidly and automatically to any given driving situation and which continuously exchanged data with the electronic engine management system. In addition to these pioneering innovations, the new automatic transmission was also much more compact and lighter than were comparable five-speed transmissions. To further improve fuel consumption and reduce harmful emissions the engines underwent more revisions. The two V8 engines were given a modified crankshaft, an optimized valve control system, lighter pistons, dedicated ignition coils for each cylinder and an improved electronic engine management system of the Motronic ME 1.0 type which integrated a hot-film air flow sensor in the place of the hot-wire air mass sensor. Modifications to the V12 engine were less extensive and affected only the arrangement of the ignition coils and the electronic engine management system. Thanks to the various modifications to the engine and the introduction of the new automatic transmission, fuel consumption for the V8 and V12 models could be cut by seven percent on average without any loss in output, and exhaust emissions by over 40 percent. September 1995 also saw the introduction of the Electronic Stability Program ESP® as an option for all S-Class models with eight-cylinder engines, a system that helped the driver to correct driving errors by automatically counteracting momentary instability by sensor-controlled brake intervention, thus contributing to active safety. ESP® was introduced as standard equipment in both twelve-cylinder models. To begin with it was available as an option with the S 420 and S 500. Then from December 1996 on, ESP® was available with all models when ordered with automatic transmission.
In addition to the model refinement package outlined above and presented at the IAA in Frankfurt, in September 1995 a new S-Class variant was premiered: The S 600 long-wheelbase Pullman. Developed as a new official representational saloon and equipped with special protection technology, this vehicle continued a long Mercedes-Benz tradition. The special-production car measured 6,213 millimetres in length and was therefore exactly one metre longer than the long-wheelbase S 600. The extra length served to benefit the rear passengers, comfortably accommodated on seats arranged in vis-à-vis format and separated if required from the driver’s compartment by a glass partition. The Pullman saloon in the W 140 series was also available as both S 500 and S 600 without armouring. The first units of both variants were produced in August 1996.
In line with tradition, the normal five-seater saloons in the S-Class were also available as armoured versions – with a choice of 5.0-liter V8 or 6.0-liter V12 engine. Production of both these armoured models began in February 1992, one year after main production start-up for the W 140 series.
Further improvements
In June 1996 the S-Class underwent further improvements. Now the five-speed automatic transmission with torque converter lock-up clutch and electronic engine management was also available for the six-cylinder models – as an option on the S 280, and as standard on all other models. At the same time the ASR acceleration skid control system also became part of the basic equipment on the six-cylinder models. Other innovations to note included sidebags as standard for driver and front passenger on all models, seat occupancy sensors to operate the front passenger airbags, an “intelligent” rain sensor that controlled the wiper interval in accordance with the volume of spray on the front windshield, and luggage nets in the trunk and front passenger footwell. Xenon headlamps with headlamp wash/wipe system and dynamic headlamp range adjustment were available as optional equipment. Externally, too, the S-Class saloons had undergone slight modifications when they were presented in June 1996; immediately apparent were the satin-finish detachable body components, now painted in the colour of the car rather than as previously in the contrast colour.
Apart from these detail improvements described above, in June 1996 a model change in the S-Class came into effect: The S 350 Turbodiesel was replaced by the S 300 Turbodiesel. In contrast to its predecessor, the new diesel model offered a turbo engine with four-valve technology and intercooling. Engine output was 20 kW (27 hp) higher, at 130 kW (177 hp); torque was increased by 20 Newton meters and available over a broad range of engine speeds; exhaust emissions and fuel consumption were much lower as a result of optimized combustion. The S 300 Turbodiesel came as standard with the electronically controlled five-speed automatic transmission.
From December 1996 the S 280 and S 320 models with automatic transmission were also equipped with the Electronic Stability Program ESP®. At the same time a new innovation had its world premiere as an additional active safety feature – Brake Assist BAS, which was fitted as standard in all R 129 and W 140 models from December 1996. Brake Assist (BAS) was able to recognize emergency braking situations and if required to boost brake power to a maximum more quickly than was previously the case, thus shortening stopping distances considerably.
A landaulet for the Pope
In March 1997 a further variant in the W 140 series was produced: The long-wheelbase S 500 landaulet, a one-off vehicle for Pope John Paul II. The landaulet soft-top was operated electrohydraulically to afford a clear view of the Holy Father seated on his centrally positioned thronal seat. It was also equipped with folding seats for two attendants.
At the Paris Motor Show in September 1998, the public was introduced to six S-Class saloons from the W 220 series, which now succeeded the W 140 series after a period of seven and a half years. Series production of the 140 models at the Sindelfingen plant was stopped at this point, and only the armoured versions and the Pullman saloons continued to be built. By September 1998, a total of 406,532 W 140 series saloons were produced, of which 28,101 units had diesel engines.
At the start of its career and particularly in Germany, the largest ever S-Class did not have an easy time – despite the car’s undeniable qualities. A valedictory appeared in the Frankfurter Allgemeine Zeitung of August 25, 1998 under the headline: “The end of the good patriarch. Sentimental farewell: The S-Class was always better than its reputation.” This obituary written by Wolfgang Peters included the lines: “...No other car offered such ride comfort and suspension, and no other car in this size category could be driven in such safety and with such agility at the same time. The S-Class was a giant that had been taught to dance on the points of its toes. [...] The new S-Class promises to be lithe and lissom: Some of us are missing the fatter version already.”
The W 140 series in the press
Auto, Motor und Sport, Germany, volume 7/1991, on the Mercedes-Benz 600 SEL: “With dimensions such as these, there is little to be said about the interior: The sense of space is almost wasteful, even more so in the rear than in the front, since the opulent height in the rear is particularly apt for giving the impression of riding in a mobile living room. … It would not be wrong here to describe this as the world’s finest car – any less would be to do Mercedes an injustice.”
Auto, Motor und Sport, Germany, issue 12/1991, on the Mercedes-Benz 300 SE: “The size and weight of the new S-Class has become almost a political issue. But in truth, on driving these factors are less noticeable than one might expect. On the contrary, it is surprising how light and easy this mighty automobile is to drive even along narrow and winding country roads.”
Road & Track, USA, December 1991, on the Mercedes-Benz 500 SEL:
“At a 70-mph cruise, the 500 SEL has the honour of being the quietest car we have ever tested – a mere 64 dBA. Helping in the serenity department is double-pane side glass, with dehumidified air sealed between the panes. It’s said to prevent fogging as well as absorb noise, and no, Mercedes assures us, it isn’t bulletproof, a question some ask when they see its thickness.”
mot, Germany, issue 13/1991, on the Mercedes-Benz 400 SEL: “With the new S-Class Mercedes once again demonstrates its claim to have invented the automobile and to build the world’s best car. When applied to the 400 SEL, one is forced to admit the claim is justified.”
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    Strong protection and extra-long wheelbase: the Mercedes-Benz S 600 long Pullman from the W 140 series was initially offered only as a special protection version.
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    Third generation: Mercedes-Benz 600 Pullman limousine (W 100 series) and the Pullman limousine from the W 140 series.
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    Outstanding twelve-cylinder in brand history: M 120 engine of the Mercedes-Benz 600 SE/600 SEL (140 model series, 1991 to 1998).
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    Outstanding twelve-cylinder in brand history: M 120 engine of the Mercedes-Benz 600 SE/600 SEL (140 model series, 1991 to 1998).
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    One-off car for the Vatican: Long-wheelbase Mercedes-Benz S 500 (140 series) as a landaulet with papal seat placed centrally in the rear.
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    Mercedes-Benz S 300 Turbodiesel (1996 to 1998). Photo from 1996. The S-Class Saloons of the 140 series were built from 1991 to 1998, a model refinement package was introduced in 1994.
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    Cut-away drawing of a front passenger airbag from a Mercedes-Benz S-Class Saloon of the 140 model series. The S-Class Saloons of the 140 model series were built from 1991 to 1998.
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    Mercedes-Benz 300 SE 2.8. From 1993 on the model was renamed S 280. The S-Class Saloon of the 140 model series was built from 1991 to 1998. The photo from 1992 shows a vehicle of the first production series prior to the model refinement of 1994..
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    Mercedes-Benz S 300 Turbodiesel (1996 to 1998). Photo from 1996. The S-Class Saloons of the 140 series were built from 1991 to 1998, a model refinement package was introduced in 1994.
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    Mercedes-Benz 600 SEL. The S-Class Saloons of the 140 model series were built from 1991 to 1998. The photo from 1991 shows  a vehicle of the first production series prior to the model refinement of 1994.
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    Mercedes-Benz 300 SEL. The S-Class Saloons of the 140 model series were built from 1991 to 1998. The photo shows a vehicle of the first production series prior to the model refinement of 1994.
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    Turbocharger of the Mercedes-Benz 300 SD as a cut-away model. The S-Class Saloons of the 140 model series were built from 1991 to 1998.
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    Mercedes-Benz S 600. The S-Class Saloons of the 140 model series were built from 1991 to 1998. The photo from 1994 shows a vehicle after the model refinement of 1994.
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    Schematic drawing of the Mercedes-Benz Brake Assist System (BAS), designed to improve driving safety, 1996.
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    Mercedes-Benz S 600. The S-Class Saloons of the 140 model series were built from 1991 to 1998. The photo shows a vehicle after the model refinement of 1994.
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    Mercedes-Benz S 280. The model was originally designated S 300 2.8 from 1992, but was renamed in 1993. The Saloons of the 140 model series were built from 1991 to 1998. The photo from 1994 shows a vehicle after the model refinement that same year.
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    Mercedes-Benz 600 SEL. The S-Class Saloons of the 140 model series were built from 1991 to 1998. The photo shows a vehicle of the first production series prior to the model refinement of 1994.
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    Mercedes-Benz 600 SEL. The S-Class Saloons of the 140 model series were built from 1991 to 1998. The photo shows a vehicle of the first production series prior to the model refinement of 1994.
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    Mercedes-Benz 300 SD. The S-Class Saloons of the 140 model series were built from 1991 to 1998. The photo shows a vehicle of the first production series prior to the model refinement of 1994.
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    X-ray image of the twelve-cylinder M 120 engine from the Mercedes-Benz 600 SE/600 SEL models. The S-Class Saloons of the 140 model series were built from 1991 to 1998.
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    Mercedes-Benz 600 SEL. The S-Class Saloons of the 140 model series were built from 1991 to 1998. The photo from 1991 shows a vehicle of the first production series prior to the model refinement of 1994.
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