A motor vehicle transmission has a differential assembly (17) in which one input, sun gear (39), of an epicyclic gear train can be selectively coupled by a sleeve (59) through a viscous coupling (55) to either an input, i.e. annulus gear (31), or to another output, i.e. carrier (36). Coupling the sun gear to the annulus gear gives a low resistance mode of operation and coupling the sun gear to the carrier gives a high resistance mode of operation. A locked mode where the annulus is locked to the sun gear is also described, together with a free mode where the viscous coupling is disconnected from both the annulus gear and the carrier. The sleeve is linked to the control of a range change gearbox to select the low resistance mode when a high range is selected for on-road use and a high resistance mode is selected when a low range is selected for off-road use.