Technical highlights of the Mercedes-Benz 300 SL Roadster (W 198 II)

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  Introduction of Dunlop disc brakes and light-metal engine block
  
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  Rear-axle suspension with single-joint swing axle
  
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  Optional removable coupé roof
  

* Roadsters and Roadsters with coupé roof.

The “Pagoda” drives up: Mercedes-Benz SL, W 113 series (1963-1971)

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  A comfortable two-seater touring car featuring high performance and optimum handling safety
  
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  Its characteristic roof shape gave it its nickname
  
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  First SL with a safety body based on Béla Barényi’s principle
  

The new model took a middle course between the concepts of the 190 SL and the 300 SL: the 230 SL, internally designated as W 113 series, held the balance between the sporty tuning of a classic roadster but added to them the comfort of a two-seater touring car featuring high performance and the most advanced features for optimum driving safety.

The 230 SL was available from summer 1963 in three versions: an open-top car with a folding soft top that could be operated with the greatest of ease – that in itself was a minor sensation; an open-top version with hardtop, and finally as hardtop coupé. The hardtop coupé had no soft top and soft-top compartment, but more room for luggage instead. All three versions could be driven with the top open. As an optional extra a rear transverse seat was available, as in the 190 SL.

The exterior of the 230 SL was characterised by clear, straight lines and the unmistakable SL face including the large, centrally positioned Mercedes star. The bonnet had a slight additional bulge in the middle to provide space for the vertically-installed six-cylinder engine. The boot was generously dimensioned. The hardtop with high windows and a roof borne up only by slim pillars conveyed an impression of lightness which simply did not match the stereotype of a sports car. With its inwardly-directed curvature it reminds one of Far Eastern temples, and straightaway the car had a nickname before it really even hit the road: “Pagoda”. In addition, because of its shape the hardtop made it easier to get in and out of the car.

Apart from the wheelbase – the magic number of 2400 millimetres was taken unchanged from the 190 SL and 300 SL models – the new SL had practically nothing in common with its two predecessors. All the same, the W 113 series was not an entirely new design since its technical concept largely conformed to that of the 220 SE (W 111/3). The SL used the “tailfin” frame-floor assembly, albeit shortened and reinforced, including front and rear wheel suspension.

In addition to the standard four-speed manual transmission, for the first time in an SL a four-speed automatic transmission was available as an optional extra. A five-speed manual transmission produced by Zahnradfabrik Friedrichshafen (ZF) was added as third variant in May 1966.

The “Pagoda” was the first SL in which sporty speed combined with safety as a design objective. Since its basis was the floor unit of the famed “Tailfin”, the world’s first saloon with a safety body, this SL also had a rigid passenger cell and crumple zones in the form of easily deformable front and rear segments. This design went back to engineer Béla Barényi, responsible for many of the safety features in cars of the Mercedes-Benz brand. As in the saloon the interior was designed so as to reduce injury hazards in accidents, by eliminating hard corners and edges. As in the previous model, seat belts were available as an optional extra. The steering gear was moved from the crash-imperilled front section to the firewall; the steering column yielding to axial compression and additionally featuring a joint that prevented the feared lance effect in an accident. In 1967, the telescoping safety steering column and the impact absorber in the steering wheel were added.

The chassis, adopted from the 220 SE (W 111) Saloon, was tuned to the requirements of the sporty car, featuring recirculating ball steering, a dual-circuit brake system and disc brakes on the front wheels. The suspension was taut, but for a sports car almost atypically comfortable. Damping was provided by gas-filled shock absorbers, and for the first time a Mercedes-Benz passenger car rode on radial-ply tyres.

The six-cylinder engine, which also came from the saloon, underwent several major changes, the most important of which was the transition from a two-plunger injection pump to a six-plunger unit. This made it possible to “shoot” the fuel directly through the preheated intake port and the opened intake valves into the combustion chamber, and not just into the intake pipe, as before. The M 127 II engine, its bore enlarged to give it a displacement of 2.3 litres, thus developed 150 bhp (110 kW) at 5500 rpm and delivered torque of 196 newton metres at 4200 rpm. Designed very sportily, this drive unit for the SL delighted in high engine speeds but did not take so kindly to underrevving.

The four-speed transmission, likewise from the saloon construction kit, was designed with a slightly lower ratio in 1st gear to achieve sportier acceleration. It sprinted from 0 to 100 km/h in 9.7 seconds. The top speed of the fabric-roofed 230 SL was 200 km/h, the hard-top version only marginally lower at 196 km/h. The variant with the optional automatic transmission reached a top speed of 195 km/h. In the eyes of sports car purists the automatic is almost immoral. But history teaches us a different lesson: by the time the “Pagoda” was discontinued the automatic transmission’s share was around 77 per cent. It was much the same with the power steering that was also available at extra cost. The W 113 series was a pioneer also on that score: all subsequent SL models always pair exceptionally good performance with highest levels of comfort. The respectable number of 19,831 units of the 230 SL were built.

On 27 February 1967, Mercedes-Benz presented the 250 SL, which replaced the 230 SL that had been produced for four years. On the outside the new car, whose series production had already begun in December 1966, was indistinguishable from its predecessor. The changes concerned mainly the engine and the brake system. Both were taken, slightly modified, from the 250 SE (W 108 III). The M 129 III engine, its displacement enlarged by 200 cubic centimetres, had the same output as the 230 SL, 150 bhp (110 kW) at 5500 rpm, but 10 per cent more torque and a flatter torque curve. It was now provided with seven crankshaft bearings for smoother operation, and with an oil/water heat exchanger as well; only the future 280 SL would be fitted with an air/oil cooler. The 250 SL thus was appreciably more flexible in operation, but did not quite reach the previous model’s top speed owing to its higher weight. The 250 SL’s top speed with four-speed manual transmission was 195 km/h or 200 km/h depending on the final drive ratio (standard: 1:3.92; optional: 1:3.69; automatic transmission: 190 km/h or 195 km/h). With five-speed manual transmission it was available in only one variant (1:4.08), which reached 200 km/h.

The changes to the brake system included disc brakes on the rear wheels as well, larger brake discs at the front, and the fitting of a brake power regulator to prevent rear wheel overbraking. As an optional extra a differential lock was now available. A fuel tank capacity of 82 litres instead of the previous 65 permitted an extended cruising range. In addition to the three body versions known from the 230 SL, the 250 SL was available as an optional extra in a fourth version, a coupé with rear seat bench, which was shown for the first time in March 1967 at the Geneva Motor Show. In this so-called California version, the necessary space for the rear bench seat had been obtained by eliminating soft top and soft-top compartment. Since the soft top could not be retrofitted, this variant promised unspoilt driving pleasure only in dry regions or with mounted coupé roof.

Less than a year after the presentation of the 250 SL, after 5196 units had been built it was replaced by the 280 SL. Apart from the model plate it could only be distinguished from the two preceding models on the outside by the different wheel hub caps.

In the wake of the market launch of the intermediate range models of the 114/115 series, not only the luxury-class saloons, coupés and cabriolets, but also the SL was powered by a 2.8-litre engine. Thanks to a camshaft with changed valve timing, the variant of the M 130 engine used in the 280 SL mobilised 10 bhp (7.4 kW) more than the base version of the 280 SE, developing 170 bhp (125 kW) at 5750 rpm. Compared with the 250 SL the power had been increased by around 20 bhp (15 kW) and torque by 10 per cent. For the first time the radiator fan was fitted with a viscous coupling which limited the rotational speed. The 0 to 100 km/h was in the vicinity of nine seconds and the top speed again came up to the level of the 230 SL, i.e., 200 km/h in the fabric-top version. Its suspension, designed for further enhanced comfort, was softer. The service intervals were 10,000 kilometres instead of 3000.

23,885 units of the fast and reliable Mercedes-Benz 280 SL rolled off the assembly line. All in all, from 1963 to 1971 a total of 48,912 “Pagodas” were built – remarkable for a sports car with such high standards. Today its high overall quality, its elegance and its clear lines make the W 113 series a coveted item among restorers and collectors.

The motor magazine “auto motor und sport”, Germany, No. 6, 1963, characterised the Mercedes-Benz 230 SL: “A sports car that does 200 km/h, goes from 0 to 100 km/h in less than ten seconds, yet has the smooth engine running characteristics and comfort of a touring car.”

A detailed test report in “auto motor und sport”, Germany, No. 21, 1963, added: “The upshot: the 230 SL is one of the most refined sports cars ever. All the same it deserves to be numbered among the truly sporty vehicles because it not only delivers sporty performance, but is as compact and safe-handling as should be expected of a sports car. [...] And finally, you can push the 230 SL at a very fast pace if you wish, but you can also maintain the slowcoach tempo that traffic conditions so frequently force upon us.”

“Road & Track” wrote the following about the 280 SL in its August 1968 issue: “The ride, over all sorts of roads, is fantastic. The body is absolutely rigid and rattle-free, regardless of which top is installed, and the supple suspension just works away down there without disturbing the superb poise of the SL.”

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  Extremely easy-to-handle folding top
  
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  Six-cylinder engine with six-plunger fuel injection pump
  
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  For the first time, automatic transmission available for an SL
  
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  Safety bodywork with rigid passenger cell and deformable front and rear segments
  
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  Numerous further safety features such as interior devoid of sharp edges and angled steering column
  
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  Disc brakes on front axle, from 1967 onwards, on rear axle as well
  

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  A total of 237,287 open-top two-seaters produced in 18 years
  
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  Engines again and again updated to the state of the art
  
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  Coupés of the SLC series available until 1981 parallel to the open-top version
  
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  The first SL with eight cylinders
  

The decision to manufacture the R 107 series (for the first time an SL series received the internal designation “R” as in Roadster instead of “W” as in Wagen = car) was taken by the Board of Management after intensive debates on 18 June 1968. At issue was whether there should be a Targa roof version, i.e., one with a removable roof panel, instead of the fabric-topped variant, because owing to higher safety standards alarming news was to be heard from the USA regarding the licensing of open-top cars.

That a decision was finally made in favour of an open-top two-seater with a fabric roof and an additional removable hard top can be attributed to Hans Scherenberg, the head of Development, who fought tooth and nail for it: “The SL gave me great pleasure, but also caused me great trouble. This was no easy decision for us,” he summed up the decisive meeting.

The history of the roadster is intimately linked to that of the coupé. For the coupé question still remained unanswered. It was not decided that day. Discussion centred around whether one should additionally, and soon, make a four-seater sports coupé based on the R 107 series, or wait for the coming S-Class (W 116) to build it on that basis. But then a production model would not have arrived until much later, in the mid-1970s.

Karl Wilfert, then Head of Body Design in Sindelfingen, developed – pretty much on his own authority – a coupé based on the R 107 and presented it one day to the Board of Management as a “rough draft”. Rejected at first, Wilfert managed to push through his idea of a sports coupé with the tenacity which was so characteristic of him.

And so just six months after its première the SL was followed in October 1971 by a comfortable four-seater sports coupé, the 350 SLC, whose unconventional lines also found it many friends around the world in the course of the years. Internally the series was designated C 107 (the “C” stands for “coupé”). Up to the windscreen its appearance matched that of the open-top variant; behind the windscreen the overall height and length grew. A flat roof spanned the four-seater passenger compartment in a gentle curve, going over into a large and very steep rear window that arched in two directions. The boot lid was slightly convex in shape, unlike the SL’s.

In the side prospect the length of the coupé is documented, firstly, by the 360-millimetre longer wheelbase (2820 millimetres versus 2460), secondly by the line of the side windows. Without interfering B-pillars they were completely retractable, as is usual in a Mercedes-Benz coupé. The SLC’s drag coefficient was better than that of the SL so that the coupé attained the same performance despite an added weight of some 50 kilograms. A particularly noteworthy fact is that it fully lived up to its classification as a “Sports Coupé”, gaining wins for Mercedes-Benz in many rallies and long-distance races.

Safety as agenda

Béla Barényi’s safety concept with front and rear crumple zones and a rigid passenger cell found expression in the 107 series in a further developed form. The backbone of the R 107 is not simply a shortened and reinforced Saloon floor assembly, as in the predecessor, but an independent frame-floor unit with a closed transmission tunnel and box-shaped cross and longitudinal members which featured differing sheet metal thicknesses and a resultant carefully defined crumple pattern.

The SL definitely had to be an open-top car, and that being the case the only protection in a possible roll-over would be provided by the A-pillar plus windscreen. They were thoroughly redesigned and had 50 per cent more strength to show than in the previously-built version. In addition, to enhance its strength the windscreen was bonded into the frame. This resulted in a remarkable power of resistance in the roof-drop test with the result that it was possible to license the open-top car for the USA even without a Targa bar. To complete the logic the rear window of the hardtop was also bonded into its frame.

In the interior there were pioneering changes to report, as well. The hard dashboard made way for an ingenious sheet-steel design that yielded on impact both in the top section and the knee area and was foam-padded. The switches and levers were recessed. The four-spoke steering wheel based on the latest findings of accident researchers, was also new. The proven impact absorber was still in place, but the steering-wheel rim, spokes, padded boss and hub were covered with polyurethane foam. As further safety feature the fuel tank was no longer installed in the rear end but above the rear axle, protected against collision. From March 1980, the anti-lock braking system ABS was offered; from January 1982, also airbag and belt tensioner.

But it was not the safety aspects that motivated customers around the world to quickly reach for the new SL. It was the promise of an open-top automobile that was a successful piece of engineering all round – and it was in fact the only one of its kind offered in the USA over a period of several years . Its distinctive front end with the dominant SL face, the wide-band headlamps and grooved turn indicator covers had a powerful aura; the lines of the low silhouette were harmonious – soft top open or closed, or with hardtop. And the very slight inward curve of the boot lid, along with the concave hardtop, were reminiscent of “Pagoda” days. The wide-band tail lights with their ribbed surface not only were largely insensitive to soiling, but additionally gave the rear end a touch of vigour.

Extremely conducive to comfort and ease of operation was the easily and speedily operated soft top, a refined version of the “Pagoda” top. It took just 30 seconds to open or close it. Folded, it disappeared underneath a cover that was meanwhile customary in the SL series.

A number of details underscored the car’s safety aspirations. The seats were available from the start with head restraints, and seat belts also were included. Physical well-being and driver-fitness safety were served by the heating system with its very spontaneous response, supported by new air ducting in the doors. Newly developed wind-deflecting mouldings on the A-pillars, which also served to channel off mud-laden water in the rain, and dirt-repelling covers on the exterior mirrors enabled good visibility. They kept the side windows clean even in inclement weather. The windscreen wipers arranged closely to each other in the centre of the car swept a respectable 70 per cent of the windscreen area, were always optimally positioned in the flow of air and did not lift off even at higher speeds.

During its 18-year “production time” (which was not planned to last that long, but in the end was indeed successful), the R 107 was driven by a whole series of six- and eight-cylinder engines. Its model designations are accordingly quite varied.

The eight-cylinder models were led by the 350 SL (1971 to 1980), whose 3.5-litre engine (M 116) already was known from the W 108, W 109 and W 111 series. The 147 kW (200 bhp) which it delivered at 5800 rpm helped the sports car, which weighed 1600 kilograms after all, to clock nine seconds for 0 to 100 km/h and reach a top speed of 210 km/h. The 350 SLC had identical performance figures.

From autumn 1971 onwards, the 450 SL was produced, initially for the US market. At 5000 rpm its M 117 engine delivered 132 kW (180 bhp) in the California version and 140 kW (190 bhp) in the version for the other states, and from 1973 on, and 165 kW (225 bhp) in the European version. Top speed was 215 km/h: it surged from 0 to 100 km/h in 8.8 seconds. In 1972, the 450 SLC, the corresponding coupé version, followed, with identical engine and identical performance. Prior to March 1973, both were destined exclusively for export to North America, after that they were included in the general sales range.

In July 1974, the SL model range was extended: the SL and SLC were now available as models 280 SL and 280 SLC with the 2.8-litre M 110 engine. It developed 136 kW (185 bhp) at 6000 rpm and had proven its reliability in the two years before in the “Stroke Eight” series W 114/115 and in the W 116-series S-Class. Both models had identical performance: the top speed was 205 km/h; they could sprint from 0 to 100 km/h in 10.1 seconds.

Thus three SL engines were now available to choose from – nothing unusual nowadays, but a real innovation for this model category in those days. Only the attentive observer could distinguish between the three variants: The 280 SL could be recognised by its tyres, narrower than those of the 350 SL and the 450 SL. In addition, the 450 SL featured a discreet front spoiler attached to the rear lower end of the front apron and which significantly increased the radiator’s air throughput.

Between November 1975 and February 1976, the fuel injection systems of all three engines were changed for better compliance with emission standards, which had meanwhile also become stiffer in most European countries. The electronically-controlled Bosch D-Jetronic was abandoned for the newly-developed mechanically-controlled Bosch K-Jetronic. The adaptation entailed minor losses in output in all three cases: in the 280 SL to 130 kW (177 bhp) at 6000 rpm, in the 350 SL to 143 kW (194 bhp) at 5500 rpm, and in the 450 SL to 160 kW (218 bhp) at 5000 rpm.

At the same time the compression ratios of the 2.8 and 3.5-litre engines were slightly reduced. In addition, the 3.5 and 4.5-litre engines were equipped with a contactless transistorised ignition system and hydraulic valve clearance compensation to facilitate maintenance.

The compression ratio of the 2.8-litre unit was raised to the old figure again in April 1978. With a few supporting measures the engine then regained its earlier power potential of 136 kW (185 bhp), which it now delivered already at 5800 rpm.

In September 1977, Mercedes-Benz launched the 450 SLC 5.0 with a V8 engine (M 117) enlarged to a displacement of five litres. A hidden innovation was the first-time application of hypereutectic cylinder contact surface machining, a special smelting process which made it unnecessary to insert cylinder liners. The engine delivered 177 kW (241 bhp) at 5000 rpm, good for 0 to 100 km/h acceleration in 8.5 seconds and a top speed of 225 km/h. The vehicle’s bonnet and boot lid were made of aluminium, and it had light-alloy wheels as standard. On the outside the 450 SLC 5.0 was recognisable by, among other things, a narrow spoiler on the rear end.