A transmission lubrication system for a vehicle providing a continuous return flow of a lubricant. The transmission lubrication system includes a differential housing, a transmission housing, a lubricant tank, a suction line, a lubricant pump, and an air suction pump. The transmission housing is connected to the differential housing in an air-tight manner and a lubricant through-passage is provided between the transmission housing and the differential housing. The lubricant tank is provided in the differential housing and has a lubricant suction opening in a lower region. The lubricant pump conveys lubricant from the lubricant tank through the suction line and conducts the lubricant to the lubrication points in the differential housing and transmission housing. The air suction pump pumps air from the lubricant tank into the transmission housing so that an excess air pressure is maintained in the transmission housing.