Mercedes-Benz W126
The Mercedes-Benz W126 is the company's internal designation for its second generation S-Class, manufactured in sedan/saloon (1979–1991) and coupé (1981–1990) models, succeeding the company's W116 range. Mercedes introduced the 2-door C126 coupé model, marketed as the SEC, in September 1981. This generation was the first S-Class to have separate chassis codes for standard and long wheelbases (W126 and V126) and for coupé (C126). The long 12-year production (1979–1991) resulted in 818,063 sedans/saloons and 74,060 coupés being built, totalling 892,123. W126 is so far the most successful and the  longest in production for S-Class. History. After the debut of W116 S-Class in 1972, Mercedes-Benz began preparing for the next generation S-Class in October 1973. The project, code-named "Project W126", aimed to provide an improved ride, better handling, and improved fuel efficiency. The oil crisis of 1973 and increasingly stringent emission and safety regulations in the United States had an important influence in developing the W126 for reduced emission and increased fuel efficiency. The W126 design team, led by Mercedes-Benz's chief designer Bruno Sacco, aimed to design a more aerodynamic shape and retain  the unmistakable S-Class design elements. The aerodynamic drag was reduced through lengthy wind tunnel testing and reshaping of front end and bumper along with hiding the wipers underneath the hood/bonnet for smoother flow. Reducing the weight was accomplished by extensive use of high-strength low-alloy (HSLA) sheet and polyurethane deformable material for bumpers and side claddings. The lighter alloy material was used for the heavily revised M116/M117 V8 engines for the reduced weight. Both had contributed to the reduction of fuel consumption by 10% as compared to its predecessor. After six years of development, the W126  was introduced at the IAA Frankfurt in September 1979. At the introduction, S-Class was available in two wheelbase lengths (standard and long) and three petrol engine options with one six-cylinder inline engine and two V8 engines. The diesel engine option was introduced in September 1981 exclusively for the North American market. At the 1981 IAA Frankfurt, a coupé version of S-Class, C126, was introduced with 380 SEC and 500 SEC. It was the first time that a coupé version was derived from S-Class chassis. At the same time, the "Energieskonzept" (Energy Concept) was introduced to improve  the fuel efficiency of S-Class through engine revisions. The W126 was revised in 1985 for 1986 model year. The revised "Second Series" model range was introduced at 1985 IAA Frankfurt with new six-cylinder petrol and diesel engines and the V8 petrol engines enlarged to 4.2 and 5.5 litres. The 5-litre V8 was carried over. The visual changes included the smoother bumpers and side claddings, revised "Gullydeckelfelge" (German for manhole-cover wheel rim) alloy wheels, and deeper front bumper with integrated air dam. The W126 generation was replaced by the W140 in 1991. Styling. From 1973 to 1975 , Mercedes-Benz designers worked on the successor to the W116. After several design concept were presented, the final design for W126 was approved and frozen in 1976. The design work for coupé began immediately after the approval and was finalised in 1977. Design patents were first filed on 3 March 1977 and later on 6 September 1977 at the United States Patent Office. Compared to its predecessor, the W116, the W126 featured improved aerodynamics with a drag coefficient of Cd 0.36 for the sedan/saloon and 0.34 for the coupés. Models. The "First Series" model range (1979–1985 for sedan/saloon  and 1982–1985 for coupé) included the 280 S/SE/SEL, 300 SD (North American market only), 380 SE/SEL/SEC, and 500 SE/SEL/SEC. The revised "Second Series" (1986–1991) with petrol engines included 260 SE, 300 SE/SEL, 420 SE/SEL/SEC, 500 SE/SEL/SEC, and 560 SE/SEL/SEC. The "Second Series" with diesel engines for North American market only included 300 SDL (a first diesel S-Class with long wheelbase) then 350 SD/SDL (a first diesel S-Class to be available in both wheelbase lengths). Engines. First Series (1979-1985) At the introduction in September  1979, the 2.8-litre DOHC six-cylinder inline M110 engine for 280 S/SE/SEL was carried over from W116. The revised M116/M117 V8 engines had a significant innovation: aluminium block without iron sleeves as found in the competitors’ engines. Mercedes-Benz developed a special silicon coating as to harden the cylinder liners against excessive wear and tear. The V8 engines were offered in two sizes: 3.8 litres (M116) and 5 litres (M117). The M116 V8 engine had a single timing chain while the M117 V8 engine had double timing chains. The frequent mechanical failure of single timing chain  in M116 V8 engine was addressed in 1982 by switching to double timing chains from M117 V8 engine. The smaller of two V8 engines was initially offered in the US market only due to Corporate Average Fuel Economy (CAFE). The 380 SEL had earned a very poor customer perception in the United States as being severely underpowered and due to the mechanical issues with single timing chain. The 380 SEL for the US market took 11 seconds to reach from standstill and had top speed of . The severe performance shortcoming of W126 with V8 engine was addressed by introducing more  powerful 500 SEL/SEC in 1984. The S-Class coupé was fitted with V8 engines only for the first time. The 3.0-litre five-cylinder inline OM617 diesel engine was carried over from W116 with same performance. The diesel engines were again never offered in the markets outside United States and Canada. This discrepancy wasn't addressed until 1994 when W140 S 350 TURBODIESEL was introduced in Europe for the first time. In 1981, Mercedes-Benz introduced the “Energiekonzepts” (Energy Concept) programme in reducing the fuel consumption. This programme revised the combustion chambers and piston heads with lower compression ratio  in the V8 engines. This revision caused further drop in engine performance. Second Series (1986-1991) For the second series introduced in September 1985, the engine range was extensively revised with new six-cylinder inline engines and enlarged V8 engines. Only 5.0-litre M117 V8 was carried over from the first series, expanding the V8 engine range to three. The revised engine range focused more on reducing pollution and fuel consumption even further. For the first time, the customers outside US and Canadian markets could choose the models with or without catalysators. The models without catalysators can be retrofitted with  catalysators at later date if the customers choose to: this retrofit method is called RÜF (Rückrüstfahrzeug — loosely translated as retrofit vehicle). The RÜF models had a mechanical switch in the engine bay to be operated by owners for running on lead or lead-free fuels, a necessary feature for driving outside Germany or in areas within Germany where the lead-free fuel wasn't widespread yet. In 1990, all engines were fitted with catalysators only and the mechanical switch eliminated. The new six-cylinder inline M103 engine had a single overhead camshaft and electronic-mechanical fuel injection and was available  in two sizes: 2.6 and 3.0 litres. The carburetted engine fitted to 280 S was eliminated, marking the end of carburetted engines for S-Class, and replaced with fuel-injected engines for 260 and 300. The V8 engines were again bored out to 4.2 litres from 3.8 litres for 420 (M116) and 5.5 litres from 5.0 litres for 560 (M117) while 5.0-litre V8 for 500 (M117) was carried over. The V8 engines were fitted with new electronic ignition system and Bosch KE-Jetronic electronic-mechanical fuel injection system, first appeared in W201 190E. The revised V8 engines except 5.0 -litre version had slight performance increase. The most powerful engine ever fitted to W126 S-Class was 5.5-litre V8, putting out 221 kW (300 PS, 296 bhp). This engine, classified as ECE-Variante (German name), has higher compression ratio of 10:5 and cannot be retrofitted with catalysator at later date. In September 1986, the ECE-Variante was superseded by RÜF-Variante, which retains the same horsepower figure without catalysator and lower figure if retrofitted with catalysator at later date. The 560 SEL with 221 kW engine was fastest large saloon, reaching 250 km/h (155 mph), until BMW  750i/750iL was introduced in 1987 with "ungoverned" top speed of 300 km/h (186 mph). Its performance was comparable to Porsche 911 Carrera 3.2 or Ferrari Mondial. In 1990, 560 SEL had a reduced horsepower figure to . For the US and Canadian markets, a new 3.0-litre six-cylinder inline OM603 diesel engine was introduced, replacing five-cylinder engine with same displacement. It was a first six-cylinder passenger diesel engine by Mercedes-Benz. This new engine was available in long wheelbase version only, 300 SDL, for the first time. For California, the diesel engines were fitted with diesel particulate  filter, a world's first for the passenger car. The new engine had an ill-gotten reputation for higher percentage of aluminium cylinder head failure due to poor placement of diesel particulate filter and due to the erosion of head gasket, allowing cooling fluid to seep in the cylinders. However, they failed to perform as designed and were removed from the engines. For 1988, the engine was revised to correct the issues and move the particulate filter further away from the engine. In 1990, the same engine was bored out to 3.5 litres as to compensate for reduced performance due  to stricter emission regulations. The bored out 3.5-litre version did not have any of aforementioned issues other than some units experiencing the unexplained erosion of head gasket. The 3.5-litre version was available in both standard and long wheelbases (350 SD and 350 SDL). Transmissions. First Series (1979–1985) The automatic transmission had four speeds with direct drive in the fourth gear for the entire run from 1979 to 1991. The 280 S/SE/SEL had 4-speed manual transmission as standard with 5-speed manual and 4-speed automatic transmissions as extra-cost options. The manual transmission was not  fitted to the V8 engines during the first series. U.S. models, including the 300 SD Turbodiesel, had automatic transmission as sole transmission choice. Second Series (1985-1991) From 1986 onward, the automatic transmission was revised to include the option of selecting S (Standard) and E (Economy) shifting points. The models, 260 SE, 300 SE, and 300 SEL were fitted with standard 5-speed manual and optional extra-cost 4-speed automatic transmissions. For one year from September 1986 to June 1987, extra cost automatic transmission option wasn't offered for 260 SE and 300 SE. The customers ordering 420 SE  could choose either 5-speed manual or 4-speed automatic transmission. U.S. models had automatic transmission as sole transmission choice. U.S. Grey Import Market. When the W126 was introduced in the United States in September 1980, Mercedes-Benz offered the smaller 3.8-litre V8 engine only as to avoid the gas guzzler penalty under Corporate Average Fuel Economy (CAFE) regulations. However, the American consumers found 380 SEL severely underpowered with slow acceleration (0–60 mph in 11 seconds) and lower top speed of . As the fear of oil crisis waned in 1982, the American consumers demanded the more powerful S-Class  models, and the grey importers brought the S-Class with 5-litre V8 engines to the United States and modified them to meet US FMVSS and EPA regulations. The result was about 22,000 W126 imported as grey market imports. Consequently, Mercedes-Benz added 500 SEL/500 SEC to the American model range for 1984 model year as to countereffect the grey imports while 3.8-litre V8 engine remained in 380 SE (standard wheelbase only) and 380 SL. In 1988, an intense lobbying effort by Mercedes-Benz and other foreign manufacturers led U.S. Congress to eliminate this loophole and revise the rules  for registered importers. Racing. Two AMG-modified 500 SEC cars raced at the 1989 24 Hours of Spa. Both cars failed to finish, with one suffering gearbox issues, while the other had issues with the rear axle. Legacy. The W126 series was the highest volume S-Class on record in terms of production. Three armoured 560 SEL ordered by Saddam Hussein had a series of pipes shooting the flames out of sides. A limited number of W126 continued to be produced in South Africa until 1993(?), two years after the introduction of W140 S-Class. No figures were given for  South African production. Nelson Mandela was given a commemorative model, a red 1990 500 SE.