Five-millionth passenger car to leave the assembly line at the Sindelfingen plant since post-war production restarted in 1946.

• March 11: The Austrian Chancellor Bruno Kreisky lays the foundation stone at the Steyr-Daimler-Puch AG plant in Graz-Thondorf for expansion of the production site. The company has a 50% holding in "Geländefahrzeug Gesellschaft mbH" (GfG), with the remaining stake held by Daimler-Benz AG. This new firm, established in February, takes up production of the co-developed off-road vehicle at the end of 1978.
• March 17 - 27: The 123 series 230 C, 280 C and 280 CE coupe variants are presented at the Geneva Motor Show.
• August 12 - September 28: The Cowan/Malkin/Broad and Fowkes/O'Gorman driver teams, both driving a Mercedes-Benz 280 E, finish first and second in the London-Sydney Rally. The so-called "Toughest Rally in the World" lasts for 6½ weeks and covers 30,000 km taking in the continents of Europe, Southern Asia and Australia.
• September 15 - 25: The 123 series station wagons, models 240 TD, 300 TD, 230 T, 250 T and 280 TE, are presented at the International Motor Show in Frankfurt.
  Simultaneously with the new estate models, the sale of another variant of the 123 series begins: the extended four-door saloons with longer wheelbase and 7-8 seats, which are initially available as 240 D, 300 D and 250.
  Other new passenger cars on display at IAA are the 450 SLC 5.0 with 5-litre V8 light-alloy M 117 engine and the 300 SD as first diesel variant of the S-Class. Bound for the US market, the 300 SD, which comes onto the market in April 1978, is the world’s first production car to have a diesel engine fitted with a turbocharger. This efficiency-boosting technology permits an increase in output of about 40 % with no appreciable additional fuel consumption.
• October: A red 350 SLC (107 series) is the five-millionth passenger car to leave the assembly line at the Sindelfingen plant since post-war production restarted in 1946. The first million were assembled within 16 years, the second in six years, the third in four years, the fourth in three years and the fifth million within two years.

300 SD

London–Sydney Marathon
1st Cowan / Malkin / Broad (33) Mercedes Benz 280E
2nd Fowkes / o'Gorman (49) Mercedes Benz 280E

12 August - 28 September: The teams of Andrew Cowan/Colin Malkin/Mike Broad and Anthony Fowkes/Peter O’Gorman celebrate a one-two victory in the marathon London – Sydney Rally in Mercedes-Benz 280 E rally cars. The "world's toughest rally" lasts for six-and-a-half weeks and covers 30,000 kilometres across Europe, southern Asia and Australia.