A universal joint (u-joint) replacement typically involves the removal of either a drive shaft or half shaft due to a malfunctioning joint. After the shaft has been removed from the vehicle, the old joint can be pressed out and a new one may be installed in its place. When this type of repair is required, there will often be an audible sound or vibration that can be felt when driving the vehicle. If a u-joint replacement is not performed after noise or vibration occur, the joint may break and the vehicle will no longer be able to move. U-joint replacement is a somewhat delicate operation because a joint that is not properly aligned during installation can fail prematurely.
Universal joints essentially consist of a set of perpendicular hinges that allow radial motion to be passed between two rods, a differential, transfer case, or wheel. These joints are commonly used in conjunction with drive shafts to transfer motion from a transmission or transfer case on one end of a vehicle to a differential on the other end. Some vehicles also use u-joints instead of constant velocity (CV) joints to connect half shafts to drive wheels. Each shaft that is used in conjunction with a u-joint has a yoke that the joint is either pressed or bolted into. When the bearings within these joints wear out, noise or vibration can occur and a u-joint replacement will be required.
The first step in any u-joint replacement is typically to remove the drive shaft or half shaft from the vehicle. In some cases, the u-joints will be bolted into the yokes on the transmission or transfer case and differential. After the shaft has been removed from the vehicle, the retainer clips can be pulled so that the old u-joint may be pressed out. A new joint can then be pressed into place, taking care to properly align the end caps to ensure proper operation. The bearings within these joints must not be contaminated with dirt or grit, as that can also cause a premature failure.
Many u-joints fail due to a lack of lubrication, so it is important to install grease fittings when performing a u-joint replacement. In some cases there will be no space to install a grease fitting without interfering with the movement of the joint and shaft, in which case a plug has to be used instead. If that is the case, it can be a good idea to install a temporary grease fitting and lubricate the joint before reinstalling the shaft on the vehicle. Other u-joints are sealed, so lubrication is not possible.