A modular mixer system which enables motor, transmission, bearing housing and impeller shaft components to be selected and combined as required for particular mixing applications. The components may be assembled to provide either direct drive from the motor to the impeller shaft contained in the bearing housing (without reduciton gears), or through a gear transmission (with an interplate and intershaft where seal removal is required), and form a mixer drive subassembly. This subassembly is mounted on mounts which provide portability; these mounts having pivotal clamps for mounting the mixer system on the wall of a tank or the like. Various fixed mounts may also be used, which are in the form of plates or pedestals which rigidly connect the mixer system to a tank or beam above the tank. In all cases the bearing housing is common and forms the core to which the components of the drive assembly and the mount are connected. The bearing housing and the transmission may be of different sizes, but are otherwise interchangeable with other components of like size.In a mixer system adapted to be mounted on a closed tank, a seal unit in the mount (a pedestal, for example) is removable without requiring removal of the motor and gear transmission from the mount by use of an interplate which closes off the gear transmission at the bottom thereof. An intershaft in the interplate transmits power to the impeller shaft which is contained in a bearing housing which is connected to the interplate and is detachable therefrom and removable from the mount. When removed, the shaft and seal are exposed for seal (or stuffing) replacement while the motor and gear transmission remain in place thereby making seal replacement much more rapid and less expensive than when the motor and gears must be removed to get to the seals.