At the turn of the year 1984/85 a new model generation appeared in the medium-size series. It became the successor of series 123, produced for nine years. The technological overall concept of series 124 showed close parallels to the compact-class. By using high-strength steel sheets as well as other weight reducing materials and by an aerodynamic optimisation of the body, a considerable reduction of the fuel consumption had been achieved even in the medium-size series.
At the same time the safety standard, reached with the S-Class and the compact-class in spite of the light construction, was further optimised. The passenger cabin of series 124 excelled by high side-impact and overturning resistance. It was equipped with ingenious deformation zones in nose and tail. The criterion in the asymmetric frontal impact with 40 % overlapping and at 55 kph was now also fulfilled by the saloons of the medium range. Furthermore, for the protection of pedestrians and drivers of two wheel vehicles, the area of a possible contact zone was concipated as resilient as possible.
As to the stylistic design there were also many common features with the compact class. In spite of this, however, the new range of Types also presented itself with independent design elements. They were used forthe first time and had a factual-functinal background true to the principle "form follows function". The characteristic shape of the tail tapering to the end and considerably rounded at the lateral top edges was aerodynamically especially favouraly. It was based on experiments in the wind tunnel. Two further typical design charactristics were the trapezoidal deeply pulled down boot-lid and the inclined inner edges of the almost square rear lights. They allowed a specially low loading sill which facilitated the loading of the voluminous boot.
A remarkable innovative construction detail were the lift controlled panorama wipers. With a 86 % wiped windscreen view it was, at that time, the largest wipe pattern in the world. Thanks to a rotational movement overlapping the vertical movement the upper edges of the windscreen could be wiped much more efficiently than with the conventional one arm wiper. Electrically heated windscreen washer jets were part of the standard equipment of all models of this series.
The front and rear axle constructions, already known from the compact-class, allowed an excellent driving performance. The new medium size models were also equipped with a damper strut front axle with individual A-arm suspension and anti-dive device as well as a multilink rear supension, in which each rear wheel was led by fife independent control arms.
The engines were mostly new developments. Only the 4-cylinder aggregates came from Types 200 and 230 E of the previous W 123 series. Besides the completely newly constructed 6-cylinder injection engines with 2.6 liter and 3.0 liter displacement, there was a new Diesel engine generation. Its 2.0-liter 4-cylinder engine had already been used in the 190 D and was now completed by a 2.5-liter 5-cylinder as well as a 3.0-liter 6-cylinder variant. From the outside all models of the series were almost completely identical. The only difference were the twin-scroll rear silencers in the 6-cylinder models and the front aprons with lamella like air inlet slots in the 300 D.
At the Frankfurt Motor Show IAA, in September 1985, eight months after the market introduction of the saloons, a 124 series estate variant made its debut. At the same time, the "Mercedes-Benz driving-dynamics concept" was presented. With its automatically controlled locking differential (ASD), its anti slip control (ASR), and its automatically engageable four-wheel drive 4MATIC it comprised three staged electronic-automatic driving-dynamics systems. The 4MATIC, the technically most expensive system of the new concept, was available for the 6-cylinder saloons and the estates of series 124. Besides the complex regulation electronics it comprised a complete additional front-wheel drive with transfer gear and differential. The conditions in the engine department of the 4MATIC-models made it necessary to integrate the compensating gear of the front drive train into the oil pan. These highly technical measures of this perfectionated front-wheel drive system, however, had its consequences in the price. Types 260 E 4MATIC and 300 E 4MATIC, which were delivered starting spring 1987, were almost DM 12,000 more expensive than their rear-wheel drive counterparts.
As it was usually the case for years with the medium-size series of Mercedes-Benz, series 124 was also available as chassis with partial bodies. They were used by body makers in Germany and abroad for ambulances, estates and other special versions. For the first time, the chassis was based on the estates and together with them they were produced in Bremen. Apart from the versions with the regular wheelbase, of which the 250 D and 230 E were available, there was again also a longer version, offered as the 250 D, 230 E and 260 E. Ambulance bodies were produced for this chassis, mainly by Binz in Lorch, Miesen in Bonn and Visser in Leeuwarden. Hearses were built on the basis of the W 124 by, amongst others, Pollmann in Bremen, Rappold in Wülfrath, Stolle in Hanover and Welsch in Mayen.
From September 1985 all petrol-engined models of this series except the basic Type 200 with carburettor could be supplied with three-way catalytic converters. An alternative option was the so-called "RÜF version", without catalyst and lambda probe, but with the multi-functional fuel supply and ignition system. This version could easily be equipped with a catalyst at a later date, an advantage for many customers as unleaded fuel was not yet available everywhere. The six-cylinder models were supplied as "RÜF versions" as standard; their performance had dropped minimally because of the conversion to the MF system, in the 230 E, the RÜF version was initially an optional extra. From September 1986, all Mercedes-Benz cars were available with a catalyst, including the carburettor version. The "RÜF versions" were still also offered, with a price reduction, until August 1989.
In 1987, the 124 series model range was again extended. First, two coupés were presented at the Geneva Motor Show in May, which completed the model line-up as a third body variant. Following that, two new saloons were shown at the Frankfurt Motor Show in September: the 300 D Turbodiesel and 300 D Turbodiesel 4MATIC, both using the 3-liter 143 hp 6-cylinder engine that had been introduced in the estates two years earlier. A world innovation was the 4MATIC version; the conventional drive 300 D Turbo ha been part of the sales program of the American distributorship MBNA since April 1986. The versions with a turbodiesel engine were optically distinguished from other types of the model series: Apart from the air-intake vents in the fairing, which are also present on the naturally aspirated versions, they had five additional air-intake gills in the right front fender.
One year later, at the Paris Motor Show in September 1988, two further models of this series were introduced: the 200 E and the 250 D Turbodiesel. In fact the 200 E had been produced for some time for the Italian market and the engine of the 250 D Turbodiesel was already in use in the compact-class. However, this engine was modified at this time, as was the 3-liter 6-cylinder turbodiesel, in order to reduce particle emissions. This was done by redesigning the prechamber to achieve more efficient combustion. A pleasant side-effect of the new Diesel technology was that the output of both engines rose by 4 hp.
In September 1988 all models of the series received more comprehensive standard equipment, including the anti-lock braking system (ABS) and a heated mirror on the drivers door. The windscreen washing system, which had been taken over from the S-Class, had a heated water tank as well as heated jets and hoses. As a part of the "Diesel '89" initiative in February 1989 the naturally aspirated Diesel engines were also given the new prechambers with angled fuel injection. Furthermore, the injection pumps were all fitted with an altitude correction jet to achieve low emissions at all altitudes. The result was that particle emissions were reduced by 40 % and the cars were able to fulfil the strict American regulations without soot filters. The new Diesel technology also had positive effects on these engines. The output of the 200 D was increased by 3 hp, that of the 250 D and 300 D by 4 hp. Emissions were reduced even further by means of a complex exhaust cleaning system using a special oxidation catalyst in combination with a finely tuned exhaust recirculating system. This system became available as an option for naturally aspirated Diesel engines from October 1990 and for turbodiesels six months later. In September 1989 at the Frankfurt Motor Show a completely revised range of the medium-sized class was presented.