Drive shafts are essentially carriers of torque. Before they became a vogue, older automobiles used chain drive and even generators to transmit power to the wheels. Drive shafts today, however, have U-joints, devices which help them to move and down during suspension. Some drive shafts also have another kind of joint, called slip joints, which allow them to adjust their lengths to the movement of the suspension.
Adjustments aside, drive shafts are of different lengths depending on their use. Long shafts are used in front-engined, rear-drive vehicles while shorter ones are used when power must be sent from a central differential, transmission, or transaxle.
Because of the load they carry, driveshafts must be strong enough to bear the stress that is required in the transmission of power. Thus, they must be periodically checked, too. Some U-joints do not require periodic lubrication as they have been designed that way by their manufacturers, but they must be inspected at each oil check nevertheless. Bad U-joints could cause the driveshaft to separate from the vehicle.