gaping of components and thus to leakage respectively to degradation of the suction properties and or to a reduced hydraulic efficiency due to the deformation of the pressure plates of the pump supported on the transmission housing since the axial forces of pump insert 5 are transmitted at a considerable distance namely at the periphery of pump insert 5 the deformation of pressure plates 7 13 in the middle region of pump insert 5 is minimized also retaining ring 23 makes possible a uniform transfer of forces at the periphery so that smaller more uniform deformations of the second pressure plate are made possible and misalignments of the pump parts are reduced thus the inventive features of this pump insert 5 having the retaining ring installation lead to a simpler structural design of transmission housing 1 and to weight optimizations since fewer components are needed also pressure plate 13 of pump insert 5 may have a smaller diameter design since the retaining ring makes it possible for the support to be manufactured with radially smaller dimensions than for example when screws or the like are used pump insert 5 is axially fixed in position in the unpressurized state i e out of operation when no axial pressure field is present in region 33 by sealing device 31 which is designed as an axially preloading element having a corresponding spring action in this inventive variant of a pump insert 5 having the retaining ring fastening pump insert 5 is pressed somewhat deeper into transmission housing 1 in order to install retaining ring 23 to that end a corresponding deflection of sealing device 31 is provided therefore in the case of.