A drive shaft and universal joints (U-joints) connect the transmission to the rear drive axle on most rear-wheel drive vehicles. Many four-wheel drive vehicles also use drive shafts and universal joints, with one drive shaft between the transfer case and rear drive axle and a second drive shaft between the transfer case and the front drive axle. The drive shaft is sometimes called a propeller shaft.
The drive shaft and U-joints provide a means of transferring engine torque to drive axles. The universal joints allow the drive shaft to move up and down, to allow for suspension travel. Some drive shafts also have a slip joint that allows the drive shaft to make minor length changes as the vehicle suspension height changes.
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