Q: How to replace universal joints in a driveshaft?
A: A press or large vise will be required for this procedure. It may be advisable to take the driveshaft to a local dealer service department, service station, or machine shop where the universal joints can be replaced for you, normally at a reasonable charge. Remove the driveshaft. On U-joints with external snap-rings, use a small pair of pliers to remove the snap-rings from the spider. Supporting the driveshaft, place it in position on a workbench equipped with a vise. Place a piece of pipe or a large socket over one of the bearing caps and position a socket against the cap. Use the vise or press to force the bearing cap out. Transfer the sockets to the other side and press the opposite bearing cap out in the same manner. Pack the new universal joint bearings with grease. Position the spider in the yoke and partially install one bearing cap in the yoke. Start the spider into the bearing cap, then partially install the other cap. Align the spider and press the bearing caps into position, being careful not to damage the dust seals. Install the snap-rings. If difficulty is encountered in seating the snap-rings, strike the driveshaft yoke sharply with a hammer. Install the grease fitting and fill the joint with grease. Do not over-fill the joint, as this could blow out the grease seals. Install the driveshaft. For double-cardan U-joints, repeat the above procedure, paying attention to how the spring, centering ball, and bearing are arranged. Both U-joints in the double-cardan assembly must be replaced at the same time, even if only half of it is worn out.
Q: What are universal joints and how can their wear be identified?
A: Universal joints are mechanical couplings that connect two rotating components that meet at different angles. These joints consist of a yoke on each side connected by a crosspiece, known as a trunnion. Cups at each end of the trunnion contain needle bearings which provide a smooth transfer of the torque load, and snap-rings, either inside or outside of the bearing cups, hold the assembly together. Wear in the needle roller bearings can be identified by vibration in the drive line, noise during acceleration, and in extreme cases of lack of lubrication, metallic squeaking and ultimately grating and shrieking sounds as the bearings disintegrate. To check if the needle bearings are worn, one can try to turn the shaft with one hand while holding the rear axle flange or the front half coupling. Any movement between the driveshaft and the front half couplings, and around the rear half couplings, indicates considerable wear. Another method is to use a pry bar inserted into the gap between the universal joint and the driveshaft or flange. Leaving the vehicle in gear and trying to pry the joint both radially and axially can reveal any looseness. A final test for wear is to attempt to lift the shaft and note any movement between the yokes of the joints. If any of these conditions exist, it is recommended to replace the universal joints with new ones.