A vehicle that includes front and rear wheels, an engine, an engine-driven rear angle drive for supplying torque to the rear wheels, and a power train for supplying torque from the engine to the front wheels. The power train includes driving and driven members and a coupler having an actuator switchable between on and off positions, the actuator, when off, permitting the driven member to turn freely and independently of the driving member and, when on, enabling the coupler to respond to predetermined minimum differences in rotational speed between the driving and driven members to lock these members together to rotationally couple the engine to at least one of the front wheels.