Since the conversion of the Höllentalbahn to adhesion operation was planned in the 1930s, a powerful tank locomotive with a high adhesive weight was required. This had to be able to pull the same loads as previous rack locomotives on the ramp with a gradient of up to 5.714 percent, but still run at modern speeds on less steep sections so that it can also be used in front of passenger trains. In order to meet the required performance, a decision was made in favor of a locomotive with a 2-10-2T wheel arrangement, in which the 20-tonne axle load possible on the Höllentalbahn was to be exploited. One consideration was to procure new examples of the Prussian T 20 or class 95 produced between 1922 and 1924. This was not implemented because the design of the T 20 was now considered outdated and its top speed of 65 km/h was not considered sufficient. In addition, an engine with three cylinders was preferred, since powerful two-cylinder locomotives tended to run very unsteady under full load on steep inclines.
The subsequently newly developed class 85 was created according to the principles of the standard program. Due to the small number of only ten locomotives, special attention was paid here to using not only individual standardized parts, but also complete assemblies from existing classes as much as possible. With a service weight of 133.6 tonnes and an axle load of 20.1 tonnes, it was to become the heaviest tank locomotive in the standard program. The power plant and chassis were taken from the pre-series models of the class 44, in which the inner cylinder acted on the second and the outer cylinders on the third coupled axle. The bar frame also consisted of 100 mm thick plates in order to be able to carry the heavy weight. As usual, a Krauss-Helmholtz bogie was used at the front end and weakened wheel flanges on the third coupled axle. The newly added trailing axle was integrated into a second Krauss-Helmholtz bogie.
The boiler was borrowed from the class 62 passenger tank locomotive. Although it was powerful, the problem that is familiar with standard locomotives also occurred here that the locomotives with three cylinders had less power than their two-cylinder sisters because the design was not designed for the even distribution of steam to three cylinders. This resulted in only 1,500 hp, which was even less than the older and lighter T 20. Nevertheless, the top speed of 80 km/h enabled a wide range of applications according to the requirements. The ten engines were used almost exclusively on the Höllentalbahn, but there they were used to pull passenger and freight trains and as a pusher locomotive. The performance spectrum ranged from hauling a 1,970 tonne freight train on the flat at 50 km/h to climbing extreme inclines of 5.55 percent with a 165 tonne car load at 20 km/h.
Even after the Höllentalbahn was electrified, the locomotives were indispensable, since the 20,000 volts and 50 hertz used here was a different current system, which required specially converted locomotives. Thus, the time of the class 85 did not end until 1960, when the Bundesbahn converted the line to the usual power system. Only road number 85 007 was used for another year on a different route and was the only example that survived afterwards.