In mechatronic hydraulic drives axial piston swash plate hydraulic machines are commonly applied in case of high external load. For modern servo hydraulic drives, problems of sensitivity of the drive and its control range increase are among the most relevant ones. To solve this problems, it is important to reduce hydraulic machines deadband. This can be accomplished by decrease of friction forces in the piston mechanism. To provide friction forces reduction, an improved piston was developed. The improved piston design promotes lubrication friction mode to occur at lower speed range due to hydrodynamic pressure. In this work the hydrodynamic force in the piston mechanism is examined. The pressure field was calculated for both improved and regular piston interfaces. It was shown, that the hydrodynamic force in the improved piston mechanism significantly exceed the hydrodynamic force in regular piston mechanism, which leads to friction forces reduction. The improved piston mechanism allows to decrease the hydraulic machine deadband and to widen its control range.