Massey Ferguson 6400-series tractors: Currently spanning 100 to 230hp (max), the MF 6400 tractor series now extends to no fewer than 12 models. Although this recent expansion of the line is important, switches from the established Dynashift transmission to Dyna-6 in 2005, plus changes made in 2007, rank as the more crucial design developments. James de Havilland reports