Abstract: A transmission comprising a torque convertor and a power shift gear box having rotatable input and output shafts, multi-ratio drive means to produce different speeds of rotation of the output shaft relative to the input shaft, said drive means including gears which are in constant mesh and clutches, which are engageable and disengageable under load, to connect the gears in a desired drive path, control means for operating the clutches of the multi-ratio drive means to change the ratio of the gear box in dependence upon an electrical signal derived from rotation of a first element associated with the torque convertor input shaft and of a second element associated with an intermediate shaft upstream of the multi-ratio drive means and downstream of a variable torque capacity clutch located between the torque convertor output shaft and the multi-ratio drive means.