Abstract: The disclosure is of apparatus and method for detecting and correcting malalignment in the drive train of a vehicle, especially a heavy-duty, load-carrying vehicle, which drive train comprises a drive shaft articulated by a universal joint and a rear end comprising a transverse axle adapted to drive wheels. Laser beam targets are affixed to the drive shaft in such an alignment that, when a laser beam is projected through them, deviations from the normal are revealed. The targets are semi-transparent members having opaque cross hairs thereon which are adjustable up and down and are mounted so that the vertical cross hairs are in line with a vertical diameter of the drive shaft. A prism-bearing target is affixed to the differential of the vehicle in alignment with the laser beam. The prism is adapted to refract the laser beam at 90.degree. and is mounted so that it can be set either at 0.degree. or 180.degree.