At the end of 2004, the MF 8200 series was replaced by the 8400 Dyna VT series, which featured Fendt's 900 series Vario transmission. The transmission’s operating logic was designed by MF itself and was similar to that of the smaller 7400 series. Driving speed could be adjusted using the left-hand stalk, the joystick on the armrest, or the speed pedal. Compared to the 7400 series, the option to use cruise control memories while driving with the pedal was added. In this mode, the speed recalled from memory was maintained constant, and the desired engine speed was adjusted using the throttle pedal.

The engines were 7.4- or 8.4-liter Sisus. The hydraulics were appropriate for the tractor’s size class. The variable displacement pump delivered 150 liters per minute, and the lifting capacity was 10,500 kg. Four electrically controlled valve blocks were standard. The new Datatronic 3 on-board computer was an affordable optional extra and could be used, among other things, to program the headland automation. Wheel slip control and a basic headland automation system, including engine speed shifting, were standard. Cab suspension was standard, and later front axle suspension was also made standard. The engine hood lifted up as a whole directly upward with the help of gas struts. The 8400 series was selected as Tractor of the Year 2005.

At the end of 2005, a transition was made to the Citius series common rail engines. The 50 km/h versions became available only at this stage.

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