Abstract: One end of a rotatable mixer drum is journalled by a spherical bearing mounted on the housing of a power transmission having its rotary output coupled to the drum by a drive shaft which axially penetrates the bearing. Arcuate splines at opposite ends of the drive shaft mesh with gear teeth of the transmission output gearing and with gear teeth carried by the drum whereby the shaft is free to deflect with respect to the transmission gearing and the drum gearing when the spherical bearing deflects as a result of drum-to-transmission misalignment. The shaft is arranged with respect to the bearing and the gear teeth engaged by its splines so that the total deflection of the bearing is divided between the ends of the shaft.