A combine harvester grain bulk tank and grain unloading system includes opposed bulk tank augers and an unloading auger formed in a grain bulk tank of a combine harvester. The bulk tank augers are for receiving and conveying grain through the bulk tank to the unloading auger, and the unloading auger is for receiving grain from the bulk tank augers and conveying grain to a grain unloading spout for grain unloading. A primary drive gear is coupled to the unloading auger and to an input, a secondary drive gear is drivingly coupled to the bulk tank augers, and a clutch is coupled between the primary drive gear and the secondary drive gear, which is movable between an engaged position for transferring power from the input to the unloading auger and to the bulk tank augers, and a disengaged position for isolating the bulk tank augers from the primary drive gear.
