In 1986, the owners at the time, the Schmidt family, sold the company to the construction machine manufacturer Orenstein & Koppel.

In 1955, Faun acquired a light Cab Over Engine from the Ostner plants for its own delivery programme, which underwent a technical overhaul in 1957 and was built until 1968.

In the mid 1950s, the company began to expand and flourish again with the manufacturing of all-terrain heavy-duty and special vehicles for the German military as well as car cranes in the weight class of 10 to 12t.

Smaller manufacturers like Faun or Kaelble could no longer compete with the big companies such as MAN, Magirus-Deutz and Mercedes-Benz and stopped making conventional trucks.

These include tractor units, ballast tractors, fire engines, airport fire engines, dump trucks, diggers, wheel loaders, vehicle-mounted cranes and crane carriers as well as communal vehicles such as compression vehicles.

In the mid 1970s, Faun supplied tractor trucks for the Soviet Union in the framework of the so-called Delta project: to develop oilfields in Siberia, build the Baikal-Amur Mainline and realize industrial projects, the Soviet Union need heavy, all-terrain and extremely robust low-bed tractor units.

O&K Group In 1984 51% shares of Faun were bought by Orenstein & Koppel a German engineering company specialized in railway vehicles, escalators, and heavy equipment.

These ballast tractors were offered with every specification possible engines from Deutz, Cummins and Detroit producing 320 hp to 812 hp, transmissions from ZF and Allison, 2 doors and 4 door cabins some models even offered Iveco cabins available in 6x6 and 8x8 configurations and had towing capacity of up to 500 tons with suitable hydraulic modular trailer these units were specially built for oversize load transporting companies like Mammoet, ALE,[3] Ibertif, Alstom, Ecnofrieght, Wynns, Arbegui, CLP Group and Sarens produced from 1984 to 1991.

After the strongly export-dependent business with heavy tractor units had to be stopped in 1991, the company has only manufactured car and mobile cranes and performed service and repair works for military special vehicles.