Transmission drive unit (10), in particular for adjusting movable parts in the motor vehicle, having a drive motor (12) and a transmission (14) which is driven thereby, wherein the transmission (14) has an output element (70) and a self-locking device (60) with a locking element (63, 55), and the locking element locks the transmission (12) with respect to torques which are applied to the transmission (12) by the output element (70), wherein the transmission (12) with its transmission toothing (47) and a motor shaft bearing (32, 28) is designed to have optimized efficiency and minimal friction, and the drive motor (12) has, as an exciter magnet, a sleeve-shaped annular magnet (18) which is arranged in a pole pot (16) which forms a magnetic return.