The six-cylinder engine of the 220 a came from the predecessor model of the W 187 series, but with a number of modifications: Compression was increased, and thanks to a sharper camshaft and larger carburettor the unit was able to raise the power output to 85 hp (63 kW).

The brake system was improved considerably. Ribbed brake drums with “turbo cooling” were fitted to the 220 a on all four wheels and ventilation slits in the wheel rims and trims ensured an adequate supply of cool air. A brake booster was fitted as standard from September 1955.

In March 1956, two years after presentation of the 220 a, the 219 and 220 S models were introduced to the public as successors to the first six-cylinder models with ponton-type bodies. The 220 S was considered the direct successor, however, as expressed in the car’s internal designation W 180 II. It was largely based on the predecessor model, but thanks to two compound carburettors, engine power had now been increased to 100 hp (74 kW). In addition to being mounted on bearings at the front of the subframe, the engine was given two additional points of support to the rear. From the outside, the only visible difference between the 220 S and its predecessors was the additional trim – thin chromium strips having been added to the beading on the front fenders and doors. Production of the convertible A and C variants began in July 1956; the coupe followed in October 1956.