The car's predecessor, the Mercedes-Benz W111 (produced 1959-1971) helped Daimler develop greater sales and achieve economy of scale production. Whereas in the 1950s, Mercedes-Benz was producing hand-assembled 300s and 300SLs along with conveyor assembled Pontoons (190, 190SL and 220) etc., the fintail (German: Heckflosse) family united the entire Mercedes-Benz range of vehicles onto one automobile platform, reducing production time and costs. However, the design fashion of the early 1960s changed. For example, the fintails, originally borrowed from North American vehicles of the late 1950s, died out within a few years as a fashion accessory. By the time the 2-door coupe and cabriolet W111s were launched, the fins lost their chrome trim and sharp appearance, the arrival of the W113 Pagoda in 1963 saw them further buried into the trunk's contour, and finally disappeared on the W100 600 in 1964.
The upgrade of the W111 began under the leadership of designer Paul Bracq. Although the fins' departure was the most visible change, the W108 compared to the W111 had a lower body waist line that increased the window area, (the windscreen was 17 percent larger than W111). The cars had a lower ride (a decrease by 60 mm) and wider doors (+15 mm). The result was a visibly new car with a more sleek appearance and an open and spacious interior.
The suspension system featured a reinforced rear axle with hydro-pneumatic compensating spring. The car sat on larger wheels (14”) and had disc brakes on front and rear. The W109 was identical to the W108, but featured an extended wheelbase of 115 mm (4.5 in) and self-levelling air suspension. This was seen as a successor to the W112 300SEL that was originally intended as an interim car between the 300 Adenauer(W189) and the 600 (W100) limousines. However, its success as "premium flagship" convinced Daimler to add a LWB car to the model range. From that moment on, all future S-Class models would feature a LWB line.
Although the W108 succeeded the W111 as a premium range full-size car, it did not replace it. Production of the W111 continued, however the 230S was now downgraded to the mid-range series, the Mercedes-Benz W110, and marketed as a flagship of that family until their production ceased in 1968.
The initial range
The car was premièred at the Frankfurt Auto Show in 1965. The initial model lineup consisted of three W108s: 250S, 250SE, and 300SE, as well as a sole W109, the 300SEL. Engines for the new car were carried over from the previous generation, but enlarged and refined.
The 250S was the entry-level vehicle fitted with a 2496 cm³ Straight-six M108 engine, with two dual downdraft carburettors, delivering 130 bhp (97 kW) at 5400 rpm which accelerated the car to 100 km/h (62 mph) in 13 seconds (14 on automatic transmission) and gave a top speed of 182 km/h (177 on auto).
The 250SE featured an identical straight-six, but with a six-plunger fuel injection (designated M129) with performance improved to 150 bhp (110 kW) at 5500 rpm, which decreased 0-100 acceleration by one second and increased top speed by 11 km/h (7 mph) for both manual and automatic versions.
Both the 300SE and 300SEL came with the M189 2996 cm³ engine, originally developed for the Adenauers. It had a modern six-plunger pump that adjusted automatically to accelerator pedal pressure, engine speed, atmospheric pressure, and cooling water temperature, to deliver the proper mixture depending on driving conditions. Producing 170 bhp (130 kW) at 5,400 rpm the cars could accelerate to 200 km/h (195 km/h with automatic transmission) and reach 100 km/h (62 mph) in 12 seconds. The cylinder capacity of the three litre Mercedes engine was unchanged since 1951. From 1965 to 1967, fewer than 3,000 W109s were produced. However, approximately 130,000 of the less powerful 250 S/SE models were built during the first two years of the W108/109's existence. By 1967 the fuel consumption of the 3 litre unit in this application was becoming increasingly uncompetitive.
The new generation
During the winter of 1967/1968 Daimler launched its new generation family of vehicles, called Stroke eight for the model year. The headline was the new W114 and W115 family, built on a new chassis, but the existing models were given an upgrade with a single engine, the 2778 cc M130.
The W108 now included 280S and 280SE, with production starting in November 1967. These replaced the 250S, 250SE and 300SE, however production of export-designated 250S would continue until March 1969. For the W109, the 300SEL finally retired the M189 engine, and received the identical 2.8 M130. In January 1968, the model line was joined by yet another car, the 280SEL. The car had the longer wheelbase of the W109, but lacked the pneumatic suspension and other features of the 300SEL. Hence the chassis code remained W108.
Performance on the cars improved. On the 280S the two downdraft carburettors produced 170 hp (130 kW) at 5200 rpm and could push the car to 185 km/h (180 on auto), whilst 0-100 was done in 12.5 seconds. The fuel-injected delivered 160 hp (120 kW) at 5500 rpm, and featured a new pump which was not affected by temperature or altitude. Thanks to the air oil filter and better arrangement of cylinders, cooling and hence economy improved. Performance of the 280SE, 280SEL and 300SEL was all but identical, a top speed of 190 km/h (185 on auto) and a 0-100 acceleration in 10.5 seconds for the W108s, the W109 due to its larger weight, took slightly longer, 12.2 seconds.
Back in 1964, Mercedes-Benz launched its top-range W100 limousine which featured a dry-sump 6.3 litre V8 engine. However the limited hand-assembly of the limo and its very large price tag limited the spread of the car, whilst the size and weight affected performance. In 1966 company engineer Erich Waxenberger transplanted the big V8 into a standard W109, creating the world's first Q-car.
Despite the large size of the W109, the automaker claimed 0-62 mph (0–100 km/h) time of 6.3 seconds. Full-scale production began in December 1967. Claimed as the fastest production sedan (top speed of 220 km/h), the 300SEL 6.3, held this title for many years. The 6.3 also introduced a new naming scheme, where the model name described the parent model and the engine displacement was separate. This nomenclature was used by Mercedes-Benz until the introduction of the class system in 1993.
The 300SEL 6.3 was a special model and production of the fuel-thirsty M100 engines was limited. As new new models were being developed the export markets had to be considered, and the United States in particular. The American car production by the late 1960s has largely switched to Big-block V8 powered cars, and Mercedes-Benz had to produce its own eight-cylinder engine to stay competitive.
The new engines arrived in late 1969, and the first was the 3499 cc M116 V8 with Bosch electronic fuel injection, producing 200 h.p, was fitted to the W109, and shown on the Frankfurt Auto Show. The car was christened as the 300SEL 3.5. Its performance included a top speed of 200 km/h (124 mph) and 0-100km/h in 10 seconds. During summer of 1970, the M116 was added to the W108 lineup on both regular and LWB, the 280SE 3.5 and the 280SEL 3.5 respectively.
The next year saw further retirements of the Pontons, the 2-door W111s and the W113 pagoda roadsters were phased out of production. This left the W108 and W109 as the sole survivors of the ageing family. However the arrival of the big-block 4520 cc 225 hp (168 kW) M117 engine allowed for a final set of vehicles to be launched in the spring of 1971, the W108 280SE 4.5 and 280SEL 4.5 and the W109 300SEL 4.5. This, was destined solely for the US market. Performance improved, top speed - 205 km/h, 0-100 - 9.5 seconds.
However as the mainstream V8 models were being introduced, production was already drawing to a close, the straight-six 300SEL was finished in January 1970, and in April 1971 the 280SEL followed. The 280SE 3.5 and 280SEL W108s were retired in summer of 1972. In September the last 300SEL 3.5 and the 6.3 rolled off the conveyors. A month later, the final 300SEL 4.5 ended the W109's output, and in November saw the final models of the W108 280SE and 280SEL 4.5s end a seven-year history.
Although many critics described the car as a "fintail without the fintails", the vehicle was an amazing success. Mostly, due its simple and square contours, it is not remembered for its looks, though some argue that it was thanks to such design that the car has such a timeless charm, but instead it was very well known for its reliability and durability, as proof of excellent German engineering. Last, but not least, the car ended nearly a full decade of the Ponton family (1953-1962), thanks to which, Mercedes-Benz went from a ruined post-WWII marque to one of European and World leaders in automotive industry. It was succeeded by the W116, a car which brought a new household name for any car, the S-class.
The W108/W109 vehicles carried over many of the basic engineering principles from previous models, but had many refinements to make them some of the most well equipped cars of the era. The 300SE and 300SEL were especially well-appointed, featuring burled walnut dashboards, automatic transmission and power windows. The 300SEL 4.5 featured a sophisticated and advanced 4.5L V8 petrol engine, which was carried over to the W116 S-class and R107 SL roadster, as was the smaller 3.5L unit.
The standard transmission for Europe was a four-speed manual gearbox. A four-speed automatic option was also available. Unusual among mainstream European automakers of the time, Mercedes developed and built their own automatic transmission system. For the six-cylinder models only, a five-speed manual gearbox was also offered, from 1969, though few customers opted for it.
When the V8-engined cars were introduced in 1970, the default transmission was the four-speed automatic, driven via a fluid coupling rather than the more usual torque converter. Buyers could still opt for a four-speed manual box, however, and benefitted from a price reduction if they did so. The 4.5 litre version (offered from 1971 but only in the United States), was fitted with a three-speed automatic box with a torque converter. This engine/transmission combination became more widely available when incorporated in the successor model.