a two - speed gerotor motor including motor valve means to communicate fluid to and from expanding and contracting fluid volume chambers . the motor includes a shift valve spool to cause the motor to operate either in the normal , low - speed , high - torque mode or in a high - speed , low - torque mode . when the motor operates in hslt mode , certain of the volume chambers comprise recirculating volume chambers . the motor defines a supplemental fluid passage through which fluid is communicated from a system charge pump to each of the recirculating volume chambers . a control valve is operable , in a shift mode to permit fluid communication from the charge pump to the supplemental fluid passage , thus preventing cavitation during shifting of the motor , especially when shifting from the hslt mode to the lsht mode .