In August 1965, the 250 S, 250 SE and 300 SE presents a new generation of models of the upper class who should succeed the tailfin 220 Sb, 220 SEb and 300 SE. All three models had in common was a designed by Paul Bracq body whose clean lines dispensed with all fashionable excess and whose restrained elegance is timeless even today. With regard to their technical concept the new types corresponded largely on their predecessors. were new except the body, the two 2.5-liter engines, which had been developed from the corresponding 2.2-liter aggregates by drilling and increase in stroke; at the injection version a six-plunger injection pump was used instead of the two-plunger pump now. Unlike its predecessor, the new 300 SE was not equipped with air suspension. But he had, as well as the two 2.5-liter types, a hydropneumatic compensating spring on the rear axle receive, which was mounted in place of the coil spring since then and kept the level of the structure regardless of the load constant.
In March 1966, the model range to include the 300 SEL was extended, which had a relation to the base model to 100 mm longer wheelbase. The extra space was serving exclusively to legroom in the rear and the entry width of the rear doors. As with its direct predecessor of the same name, was also in the new 300 SEL air suspension as standard. Factory Internally the models with conventional suspension in the W 108 were summarized, the air-sprung 300 SEL, however, was associated with the designation W 109 an independent series.
In the years 1966 and 1967 originated in Sindelfingen two very special versions of the 300 SEL – both were not intended for mass production and have been developed especially for the Vatican. In June 1966, a Landaulet was completed with standard wheelbase, which differed from the production sedan only a single seat in the rear and the extending to the front edge of the rear doors Landaulet roof. Almost a year later, in May 1967 two identical six-seater limousine came to delivery, which were built on a lengthened by 650 mm underbody and had modified rear doors and two folding seats in the rear. The landaulet acted next to the 600 as a second car for the pope himself, the Pullman limousines were used for transporting Vatican guests.