In 1965 the Deutz 05 series was introduced. Both the technical and the stylistic changes compared to the previous models were minor. The appearance looked even more outdated than that of the competitors introduced at the same time. The engines of the 812 series had already been fitted in the D30 and D40 models the year before. Now the 2505, which replaced the D25, also received the new engine. With the 05 series, the engines were equipped with an axial fan. In Finland the SAE power ratings declared for the 3005, 4005, and 4505 models were 31, 47, and 47 hp respectively.

The 05 series featured a dual clutch, but on the 2505 the power take-off depended on the driving clutch. The 2505–4005 models each had a total of 8 forward and 2 reverse gears. The 4505 came with the more heavy-duty T 50 transmission, which offered only 6 forward and 2 reverse gears. In the 1967 model year the 4505 was upgraded to the TW 50.1 transmission, with 8 forward and 2 reverse gears. The 4505’s hydraulics were also brought into line with the four-cylinder models in the range. Compared with the 4005, more power was extracted from the 4505’s engine by raising the maximum engine speed, since the peak torque remained the same. The 4005 was at one time the best-selling tractor model in Germany.

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