Abstract: A hydrokinetic torque converter has a rotary housing which is connectable to the crankshaft or camshaft of a combustion engine in a motor vehicle to drive the input shaft of the transmission. The housing confines a turbine, a pump, a stator (if necessary) and a lockup clutch between a radially extending wall of the housing and the turbine. A piston of the lockup clutch is movable in the axial direction of the housing and defines a first fluid-filled compartment with the turbine as well as a second fluid-filled compartment with the wall of the housing. The force which is required to engage, to partially disengage or to fully disengage the lockup clutch is reduced by the provision of one or more profiles on the piston and/or on a friction disc of the lockup clutch which extends or extend into the adjacent compartment or compartments to influence the speed of circulation of fluids in the respective compartments and/or the fluid pressures acting upon opposite sides of the piston.