In star epicyclic gearboxes, low frequency subsynchronous (below turbine speed) vibrations can be predominant. Turbo-generator gear unit testing shows that these low frequency vibrations may occur even when the rotating components are balanced precisely. In star epicyclic gearboxes of Stoeckicht design, splined couplings between the ring gears and output shaft are used to float the ring gears for load sharing. The sub-synchronous vibrations that arise from such components are transmitted along with the mesh frequency vibrations to the turbine rotor bearings. When the amplitude levels of these vibrations and their harmonics exceed a certain limit, the life of these bearings is significantly reduced. To reduce the vibrations from the dynamic eccentricity of ring gears and splined couplings the design is changed.