Abstract: An apparatus such as a farm implement or other mechanical device subject to varying loads and power requirements has an hydraulic circuit which automatically shifts two or more hydraulic motors from a normal series operation at high speed to a parallel operation at reduced speed but higher torque in response to increased fluid pressure upstream of the motors. In a disclosed embodiment, a valve is connected to block flows from the fluid source to inlet of one motor and from outlets of both motors directly to drain under low pressure conditions but to shift to allow two parallel flows to the two motors upon increase in pressure in the flow from the source. A third motor driving an auxiliary device such as a material feed is by-passed in the parallel-flow condition.