A drive shaft must smoothly transfer torque while rotating, changing length, and moving up and down. The different
designs of drive shafts all attempt to ensure a vibration-free transfer of the engine's power from the transmission to the differential. This goal is complicated by the fact that the engine and transmission are bolted solidly to the frame of the car, whereas the differential is mounted on springs. As the rear wheels go over bumps in the road or changes in the road's surface, the springs compress or expand, changing the angle of the drive shaft between the transmission and the differential, as well as the distance between the two. To allow for these changes, the Hotchkiss-type drive shaft is fitted with one
or more U-joints to permit variations in the angle of the drive, and a slip joint that permits the effective length of the drive shaft to change.