a controllable clutch includes a plurality of piston members , a plurality of oil passages communicating with the piston members and a plurality of grooves for receiving a roller from the piston members . the piston members are disposed in one of an inner race and an outer race . the pistons in the piston member can extend in the same rotational direction to form a one - way clutch in that direction . alternatively , the pistons in the piston members can extend in opposite rotational directions to form a clutch . or , by selectively applying hydraulic fluid to the piston members , a one - way clutch can selectively be formed in either rotational direction .