| The world premiere of the new SL-series 129 in March 1989 belonged to the main attractions of the Geneva car salon. The completely reconstructed types 300_SL, 300_SL=24 and 500_SL showed no common features with their preceding models except for their overall concept. Just like 18 years before, when the 350_SL demonstrated a great number of innovative construction details in automotive progress, the SL of series 129 now also was a completely new car.
The new SL-generation convinced by a harmonic and very successful stylistic shape. It expressed dynamics, sportiness, but also comfort and elegance. On the one hand, the design presented itself traditional, on the other hand, its new solutions of many details looked far into the future. Thus, for instance, the radiator grill, the legendary trade mark of the SL-types, had been newly interpreted on the basis of remaining traditional shapes. In contrast to the preceding types, where the broad chrome frame and the star were dominant, the radiator cowling was now organically integrated into the engine bonnet. The star, now the only chrome decoration of the car, had been completed by horizontal lamellas of anodized aluminium.
Considerable improvements as to passive safety could be achieved in comparison to the preceding models. With high efforts in development the exemplary safety standard of the limousines and coupes could also be reached in the SL. Since there was no normal roof unit, a basically different body structure and therefore an intensive development work was demanded. The envisioned impact-resistant passenger compartment was achieved by combining several structural elements. Included were, first of all, a specially stiff body platform with high-strength metal sheets, large supporting elements as well as flexural resistant transitions from the A-pillars and the rear side parts to the frame side rails. The doors played a decisive role. By a well-devised bead of the door shell inner panel they functioned as a pressure resistant link between the front wall pillar and the centre pillar. Thus they contributed to preserving the survival space in case of a collision.
A further point of development was the realisation and development of the forward structure, already well-proven in the limousine series. It was based on the fact that front-end impacts are often offset. By reinforcing the front end cross-ties, the side farther away from the front crash is now able to absorb part of the impact energy.
An integral part of the safety concept was the automatic rollover bar. It had been realised in car manufacturing for the first time. Its task was to secure the survival space of the passengers in case of a rollover. In order not to spoil the joy of driving in an open car by a fixed and inflexible rollover bar, a flexible solution was realised. Now the rollover bar is only activated in case of need. During the rest state the safety bar, consisting of a U-shaped high-strength steel pipe clad with PU-foam, was positioned in front of the folding-top compartment. It formed the end of the tail and was in one line with the folding-top compartment lid.
In case of an imminent rollover the rollover bar was released by an electromagnatic sensor system. It folded up within O.3 seconds by the force of prestressed springs and was secured by ratchets. The high-strength centre pillars served as basis for fixing and support. They were extensively linked with the rear frame side rails. In addition to the automatic ,crash-triggering" in case of need, there was also a manual operation. If desired by the driver, it could be activated by a switch. For this ,comfort operation" the folding up and the retracting was regulated by a hydraulic element.
But the survival space in case of a rollover was not only secured by the rollover bar. It was also supported by a special construction of the A-pillars. They consisted of high-strength metal sheets and were reinforced with high-strength tubes at the area of the upper door edges. Together with a two-tray front roof frame and a windscreen bonded with the body a very high stability was reached even if force was applied on one side only.
Due to the rollover bar, the coupe hardtop had no more decisive function for the stability of the passenger compartment any more. Therefore, it now consisted of all-aluminium and weighed 10_kg less than the hard top of the preceding model, even though it had a larger window area. This was of great advantage for mounting and removing the top. Altogether the reduction of weight was an important factor. By consistent light-weight construction and the extensive use of high-strength sheets a body shell structure weight of 405_kg could be reached. In spite of a significantly improved structure safety this was only 20_kg more than that of the preceding model.
A further crucial point for the specific safety of the SL-passengers were the newly developed integral seats. Due to their supporting structure and high transversal rigidity they guaranteed higher protection in case of a lateral impact. The supporting seat frame consisted of fife magnesium diecast parts of high resistance. It was further possible to integrate the seat belt system with the pretensioning device, the belt adjustment combined with head rest adjustment as well as the fully electrical adjustable functions into the seat.
In addition to safety, comfort had not been forgotten. The fundament had already been laid by the development of the body structure. In order to reduce the vibration and torsion behaviour typical for open vehicles, additional diagonal struts were built into the specially critical body areas. In the front structure the front axle support was linked with the door sills by two tread struts. In the rear two tube struts between the door sills and the spare-wheel recess took over the same task. With these measures the torsional rigidity could be reduced once more by 30_% as against the previous model. All in all an overall resistance similar to that of the limousine was achieved.
The newly constructed electrohydraulic top was especially convenient in operation. It was part of the standard equipment of the new SL. By manoeuvring just one switch the folding top could be opened within 30_seconds and concealed in the top compartment or taken out of the top compartment and closed again. At the same time the side windows and the rollover bar were lowered and then brought back into basic position. The energy was provided by an electrically controlled hydraulic pump, which was installed in the spare wheel compartment together with the oil reservoir. 17_ limit switches monitored the microprocessor controlled motions. The hydraulic system comprised 15_pressure cylinders and 11_electromagnetic valves.
A further innovation, used for the first time for the SL-series 129, was the so-called ,windbreak". It was not a high-tech miracle as against the electrohydraulic top, yet also developed in painstaking detailed work. The windbreak consisted of a framed air-permeable grid. With a few flicks of the wrist it could be fixed at the rollover bar. When set up, driving comfort in the open car was considerably increased. Wind noise and draught were reduced to a minimum.
Further operational conveniences were the electrical window lifter and the electropneumatic central locking system. Both were part and parcel of the standard versions of the new SL-models. The basic equipment of the 500_SL also included an electric steering column adjustment. Thus the steering column could be adapted in height, tilt and longitudinal direction to the needs of the driver.
As to its technical equipment the SL presented a combination of well-proven and newly developed components. The chassis corresponded basically to the ones known from the limousines of series 201 and 124. Thus the damper strut front axle and the multilink rear suspension were also built into the new SL-models and guaranteed excellent driving performance. Numerous parts had been adapted to the changed installation as well as stress and strain conditions. The axle geometry was also adjusted to the special demands of driving performance and convenience.
On demand, a newly developed additional system was available. It demonstrated the level of chassis engineering realisable at that time. Three sub-systems had been combined with each other. The level adjustment and regulation of front and rear axle was responsible for keeping a constant vehicle level on the running engine. With the automatic speed-sensitive levelling system the vehicle level was lowered or increased according to the actual speed. When driving on bad roads the level could be increased by 30_mm. When driving more than 72_km/h it was first lowered to normal level. At 122_km/h it was once more lowered by 15_mm. The third component, the ,adaptive damping system" with adjustable bumpers and a complex electronic regulation, made it possible to adapt damping in a fully automatic way and within fragments of seconds to the actual needs. Fife sensors were constantly detecting the driving conditions.
According to their sportive demand, all models of series 129 were equipped with 16_inch all-aluminium wheels in 15-hole design and with wide base tyres of dimension 225/55_ZR_16. The wheels were larger than those of the previous models. Thus more generously dimensioned brakes could be installed, quite in line with the improved power of the SL. A novelty were the front fixed -caliper disc brakes. They consisted of four pistons, with two pairs having different diameters respectively. This construction, used for the first time for a Mercedes-Benz passenger car, guaranteed a homogenous wear of the brake pads and a more efficient use of the lining volume. In all three models the anti-locking system was part of the standard equipment.
In the range of engines, too, novelties were combined with well-known constructions. All three aggregates of the original model program were equipped with a regulated catalyst emission control system. The 3,0_ltr.-6_cyl.-engine of the 300_SL had proven itself for years, not only in the preceding model but also in the limousines of series 124 and 126. In the new SL it was used in a redesigned version. The most important improvements were a restructuring of the combustion chamber. Thus the untreated emission of unburned hydrocarbon could be reduced. Furthermore the emission control system was changed. After dropping the upstream, thermal much stressed pre-catalyst as well as the enlarged section of the exhaust pipe, the new twin-scroll catalyst could now improve the nominal capacity of the M_103 from 180_PS to 190_PS.
The 3,0_ltr.=four valve engine of the 300_SL-24 was a new construction. It had been developed from the M_103. In its engine gearbox unit it corresponded largely to its two-valve counterpart. The four-valve cylinder head was new, as well as the map-controlled adjustment of the intake cam. In combination with a higher compression and an electronic injection system with antiknock control the four-valve M_104 showed an improved power efficiency as against the M_103 with 40_PS. Thus the driving performance of the 300_SL-24 was more sportive with almost the same fuel consumption. It was, however, almost 10_000,-_DM more expensive.
A special novelty at the Geneva car salon was the 500_SL, the top model of the new SL-series. It was provided with a 326_PS strong 5,0_ltr.-V8-four-valve engine and thus the most powerful series passenger car of Mercedes-Benz. The construction of the V8=four valve M_119 was based on the 5,0_ltr.=all-aluminium engine M_117 which had proven itself for more than ten years. In order to obtain an even higher power, the crankcase, crank shaft and the connecting rod had been considerably modified.
The two four-valve cylinder heads were a new construction. Like the six-cylinder they were provided with an adjustable intake cam. The significant increase in power and torque was based on the change to four-valve technology, but also on the antiknock control. In addition, a new two-disc air filter with a reduced suction resistance as well as changes in the emission control system were responsible for it. As the two six-cylinder aggregates, the four valve=V8 had received a twin-scroll catalyst with a larger diameter. The pre-catalyst had been dropped. The power range of the 5,0_ltr.=four valve engine enabled a breath-taking driving performance. Thus the new 500_SL stood in great distance to its preceding models. It linked with the tradition of its legendary ancestor. Accelerated from a standing position, the top model reached 100_km/h in 6.2_s. The maximum speed was electronically limited to 250_km/h.
The production of the new SL-model was not carried out in Sindelfingen as with the previous models. Due to capacity reasons it was transferred to Bremen. There the production of the main series started already in March 1989.
The most favourable resonance of the SL-series 129 can be seen by the fact that the yearly production capacity of 20,000 cars was fully utilised only a short time after its presentation. Therefore a time of delivery of several years had to be taken into account. Shrewd speculative dealers found buyers for their SL even by adding fife digit sums to the original price. This did not just happen once and was the down-side of the great demand.
Since October 1992, three and a half years after its presentation in Geneva, the SL was also available with the 400 PS strong 6,0_ltr.-V12-engine. It had already proven itself in the limousines and coupes of the S-class series 140. The injection system was modified to reduce the pollutant emission even further. The mixture enrichment at full throttle was dropped. Thus the most powerful engine of the passenger car selling program now mobilised ,only" 394_PS, 14_PS less than the original version.
In spite of this slight power reduction the V12-aggregate still guaranteed tremendous driving performance. There was, however, only a slight distance between the 600_SL and its smaller brother with the V8-engine. The acceleration of 6.1_s was slightly lower, but the maximum speed was also deactivated at 250_km/h. Thus the twelve cylinder was excellent in smooth driving and turbine-like power performance. The extra charge of more than 60,000,-_DM, however, made it more a prestige object. After all the new top model of the series had a range of extras in its standard equipment. With the 500_SL one had to pay them on top. Besides the adaptable damping system with level adjustment at the front and rear axle, the basic equipment included among other things_ speed control, automatic inside day/night mirrors, headlight cleaning system, automatic air-conditioning, leather upholstery and seat heating. From the outside, the 600_SL could only be recognised by the type label and the two "V12"-emblemes, allocated close to the air outlet openings behind the wheel cutouts. Otherwise there was no outside distinction from its sister model.
When the new top model appeared, the 500_SL was also slightly redesigned. The previous version with the V8=four valve with Bosch KE=Jetronic was replaced by the ,uniform deck engine". It was already known from the 500_E, from the limousines and coupes in the S-class. A characteristic feature of the new engine was the modified crank case. Its deck height now corresponded to the 4,2_ltr.-aggregate. Another characteristic was the electronic injection system Bosch LH=Jetronic with air mass sensors. As in the V12= engine the full-throttle enrichment was dropped in order to reduce pollutant emission. This measure did not only concern the SL but all other passenger car types with V12= and V8=aggregates. In the case of the 5,0_ltr.=engine this meant a power reduction of 6_PS, which practically, however, could not be felt in the driving performance.
In June 1963 the type designations of the SL-models were also adapted to the new nomenclature system. It had been introduced at the presentation of the C-class. The legendary and traditional letters ,SL" were now put before a three digit number. So 500_SL became SL 500_. At the same time there were also technical changes. Both six-cylinder models received new engines. The two-valve and four-valve variants of the proven 3,0_ltr.-aggregate were replaced by two four-valve engines with 2,8_ltr. and 3,2_ltr. displacement. Like the previous four valve engine they had belonged to the engine series M_104 and had already been used in other series.
The 2,8_ltr.=engine had been used since October 1992 in series 124 and in the S-class limousine 300_SE_2.8. It exceeded the two valve engine with stronger displacement from the type family M_103 as to power and torque. However, it did not show a higher fuel consumption. The 3,2_ltr.=aggregate of the SL 320 had proven itself since March 1991 in the S-class models 300_SE and 300_SEL. Its nominal capacity had remained the same in comparison to the former four valve engine. It was, however, reached 900_/min earlier. The torque maximum was considerably higher and was shifted towards lower numbers of revolution. All in all the new six-cylinder engines achieved a significant improvement of power and driving performance. The SL_280 was the only type of the series still available with the fife-speed manual gearbox. All the sister models now had standard automatic transmissions.
At the IAA in Frankfurt, in September 1995 the SL- models presented themselves in a new optical and technical version. The model improved variants showed a modified body design, a rich interior equipment and a perfect technology.
The body design was only slightly modified. But newly designed front and rear bumpers, colourless glass covers at the front turn signal lights and a discreetly changed radiator grill with only six lamellas made the SL look even more dynamic. The side panelling as well as the bumpers were not painted in a contrast but in the body colour now. The ventilation orifices were changed and were a conspicuous characteristic of the model improved types. Other novelties were the uniformly red bichromatic rear lamps and the new all-aluminium wheels in 12-hole design. All SL-types were now equipped with these wheels. On demand, a glass sunroof with roller sun visor was available. It could be mounted in stead of the normal aluminium hard top. In the interior the door panelling, the steering wheel and the seat design was modified.
Xenon gas discharge head-lamps, which had been introduced in the new E-class for the first time only a few months ago, were now also available for the S-class. As against traditional halogen head lamps the new xenon lamps achieve twice as much light intensity. Thus they provide a better and brighter road illumination. A dynamic headlight-range adjustment prevents you from being dazzled by the oncoming traffic. A world novelty was introduced in the SL-class and the S-class at the same time. As the first car manufacturer in the world Mercedes-Benz was able to present a speed control for 30km/h zones. It now belonged to the standard equipment of all SL-types.
The engines and the gearbox of types SL_500 and SL_600 were technically improved. For both new models a completely newly developed 5-speed automatic transmission with converter lockup clutch was used. It replaced the previous gearbox with hydraulic control. The main piece of this technical miracle is an electronic gearbox control which adapts the shifting quickly and automatically to every driving situation. It maintains a permanent data exchange with the electronic engine control. Besides these trendsetting novelties the new automatic transmission is considerably more compact and lighter as against the transmission with fife driving positions. The engines were once more redesigned in order to reduce fuel consumption and pollutant emission. Therefore, the 5,0_ltr.- V8-engine received a modified crankshaft, an optimised valve control, a weight-reduced piston, direct-fire ignition coils for each cylinder as well as an improved electronic engine control - type Motronic ME_1.0. Due to the many modifications of the engine and the use of the automatic transmission the fuel consumption in types SL_500 and SL_600 could be reduced by 10 % with no change in power.
Also since September 1995 the ,electronic driving stability program" was available for both models. It helps the driver in case of a mistake. It counterbalances the unstable moment by a sensor controlled well-aimed brake intervention, thus contributing to driving safety. For the SL_500 this stability program is available on demand. For the twelve cylinder it is part and parcel of the standard equipment.
Since June 1996 the new automatic transmission with electronic control was also available for the six-cylinder models SL_280 and SL_320_; in the 2,8_ltr.-variant on demand, in the SL_320 as standard equipment. Since December 1996 the six-cylinder SL-types provided with this transmission can also be equipped with the new driving dynamics program. At the same time a world novelty and further improvement is used which also helps active safety - the braking assistant. Since December 1996 it is installed in the standard versions of all models of series 129 and 140. In case of need the braking assistant BAS is capable of recognising emergency braking and of building up the maximum break boost automatically and faster than in previous times. Thus the braking distance of the vehicle is drastically reduced.
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