Drive Shaft and Universal Joints
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.
Check your vehicle's owner's manual for maintenance intervals on the drive shaft and U-joints. Many vehicles have U-joints that are "lubed-for-life" from the factory and do not require periodic lubrication. Even if the U-joints can't be lubricated, they should at least be inspected at every oil change. Also, SUVs and pick-ups often have lubrication fittings on drive shaft slip joints. Ask for these to be lubricated when bringing your vehicle in for service. Replacement U-joints often come with lubrication fittings, so if the U-joints are replaced on your vehicle, make sure they're lubricated at every oil change.
Symptoms of a bad universal joint include a repeating squeaking sound when accelerating from a stop, a heavy clunking noise when shifting from drive to reverse or visa versa, or a shuddering sensation when accelerating or driving. If your vehicle shows any of these symptoms, have it inspected as soon as possible by a qualified service technician. Neglecting the warning signs of a bad U-joint could cause the drive shaft to separate from the vehicle, making repairs more expensive and possibly damaging the vehicle.