Abstract: A transmission testing apparatus having at least one inertia flywheel having a shaft capable of being coupled to the output shaft of the transmission being tested. The transmission is mounted on a removable plate on an adjustable bulkhead supporting a prime mover, such as an internal combustion engine, and having an output shaft coupled to the input shaft of the transmission. The bulkhead is adjustably positionable such as to align the transmission output shaft with the inertia flywheel shaft. Alternatively, the apparatus comprises two upright members each provided with a shaft driven inertia flywheel such that each of the output shafts of a transaxle transmission may be coupled each to one of the two inertia flywheels.