142 of the chassis were used for the Brummbär and 278 for the Panzer IV/70(A). Auxiliary engine removed and (turret could only be hand cranked) replaced by extra 44 gallon fuel tank. All vision ports deleted except gunners. Nähverteidigungswaffe was added as a smoke discharger and close defense. Steel road wheels, vertical exhaust mufflers, and hull sides extended beyond the front hull plate were changes made during production. Return rollers reduced to 3 on later models. Side skirt on many vehicles was heavy gauge steel mesh.
Starting in the Summer of 1944 a new wider Ostkette (Eastern Track) was installed to allow for better performance in snow and ice. Other models were also retrofitted with them.