Abstract: Disclosed systems couple two rotational shafts in axial alignment with each other such that torque can be transferred between the shafts without undesired loading occurring. A shaft coupling system can include an annular mounting housing positioned around a juncture of two rotational shafts with bearings positioned between the shafts and the housing so that the housing prevents radial motion of the shafts while allowing the shafts to rotate about their common axis. One shaft can be coupled to an engine and the other shaft can be coupled to a shaft-driven device such as a hydraulic pump. One shaft can be smaller in diameter and piloted into a recess in the end of the other shaft. In some embodiments, the two shafts have about the same diameter and are linked via a torque coupler within an annular mounting housing that allows rotation but limits radial motion of the shafts.