Mercedes-Benz S-Class, W 126 series (1979 to 1991)
In September 1979, Daimler-Benz presented a new S-Class generation at the IAA in Frankfurt. The range of models available in the W 126 series was comprised initially of seven vehicles: Choice was from four engines (from the 2.8-liter six-cylinder carburettor unit with 115 kW/156 hp to the 5.0-liter V8 light-alloy engine with direct fuel injection and 176 kW/240 hp) and two body variants – in addition to the normal version, a lengthened variant, as had traditionally been the case with premium-segment saloons for generations. In this case, lengthening of the wheelbase by 140 millimetres was more apparent than otherwise and as usual the extra space served exclusively to increase legroom in the rear and the entry width for the rear doors.
In addition to improving ride comfort and safety, development of the new model series focused on decreasing energy consumption. The use of weight-reducing materials and an aerodynamic body optimized in the wind tunnel (cd= 0.36, compared with cd= 0.41 in the W 116 series) helped the new S-Class achieve a ten-percent reduction in fuel over its predecessor models. The two eight-cylinder engines of the predecessor series were replaced with two redesigned units with larger displacement and light-alloy crankcase.
The 5.0-liter engine, which replaced the 4.5-liter cast iron unit, was already familiar as the power unit from the 450 SLC 5.0, while the 3.8-liter light-alloy engine was developed based on the long-serving 3.5-liter V8 with cast iron block. With both higher output and reduced weight, the new V8 engines could now achieve improved performance while at the same time using less fuel. The carburettor and injection versions of the 2.8-liter six-cylinder remained in the range unchanged.
Diesel for export
The W 126 series also saw development of a diesel version for export to the USA. Like its predecessors, the 300 SD Turbodiesel offered a turbocharged 3.0-liter five-cylinder engine, though with output now increased by ten hp (7.4 kW) to 125 hp (92 kW).
Chassis design was essentially the same as for predecessor models. The new S-Class saloons also featured a diagonal swing-axle at the rear and double-wishbone front suspension with zero-offset steering. The 5.0-litre models were again fitted with the coupled-link axle.
The body design incorporated state-of-the-art findings in safety research. Thanks to its new design principles the passenger compartment was now able to withstand the so-called “offset crash” unscathed at a speed of 55 km/h. The W 126-series saloons were the first production cars worldwide to meet the criteria of the frontal offset crash.
Many of the characteristic design elements of the S-Class are to be found beneath the waistline. For the first time, a Mercedes-Benz passenger car had no bumper bars in the classical sense, having instead generously proportioned plastic-coated bumpers that were seamlessly integrated into the car’s front and rear aprons. Broad lateral protective strips made of plastic created a visual link between front and rear aprons, positioned at bumper height between the wheel arches.
At the IAA in Frankfurt of fall 1981, two years after the debut of the W 126 series, an elegant coupé was added to the family, available only with eight-cylinder engines. Both V8 units underwent comprehensive revision as part of the recently initiated “Mercedes-Benz Energy Concept,” a program geared to reducing fuel consumption and harmful emissions. In addition to an increase in compression, the list of improvements included camshafts with modified valve timing, air-bathed injection valves and electronic idle speed control. Camshafts with modified valve timing enabled maximum torque to be achieved at a lower engine speed and in the case of the 3.8-liter engine torque was even increased. This unit was subjected to particularly thorough revision: In order to achieve a more favourable volume-to-surface ratio, the bore was reduced and the stroke increased. The modified 3.8-liter V8 thus benefited from a slightly larger displacement. But by way of compensation for their significantly better fuel economy, the two eight-cylinder units were obliged to accept a minor drop in output. In both cases, rear axle ratios were tuned to meet the modified characteristics of the engines and were significantly longer. And the two six-cylinder units also saw a whole series of minor modifications that likewise led to fuel economies, even if these were less dramatic. These measures did not affect power output.
Four years after the launch of the Energy Concept the company carried out a comprehensive model refinement package, so that in September 1985, once again at the IAA in Frankfurt, it was able to introduce a completely revised S-Class line-up. Visual aspects were subjected to moderate revision; first and foremost this affected the bumpers and protective side moulding, but also the wheels, which were changed from 14 to 15 inches. This also brought with it a safety element, since it allowed larger brake discs to be fitted. Top priority, however, was give to the restructuring of the engine range.
Two newly-designed six-cylinder units, which had been premiered nine months earlier in the mid-range W 124 series, now replaced the trusty 2.8-liter M 110 engine. In the place of the carburettor version came a 2.6-liter direct injection unit, while the parallel-developed 3.0-liter unit became successor to the injection variant of the M 110. A new addition to the range was the 4.2-liter V8 engine, developed by increasing the bore of the 3.8-liter unit and now fitted to the S-Class saloon, the SEC coupé and the SL. The 5.0-liter engine was also modified. Now equipped with an electronic ignition system and the electro-mechanically controlled Bosch “KE Jetronic” injection system, it generated an output of 180 kW (245 hp).