Abstract: Apparatus for providing drive assistance in a vehicle having a main transmission that is mechanical. The apparatus comprises a hydraulic motor of the type having radial pistons that is powered by a main pump. The pistons can be retracted into their cylinders in a free-wheel configuration of the motor or they can co-operate with the reaction member of the motor when they are in a working configuration. The apparatus comprises means for implementing successive stages of a sequence for causing the motor to pass from its free-wheel configuration to its working configuration. The sequence comprises an initialization stage in which the case of the motor is filled with fluid at a “service” pressure by means of an auxiliary duct and a service duct, and in which the main feed and exhaust ducts of the motor are placed at a filling pressure that is lower than the service pressure.