A universal joint, or U-joint, is used to allow flexibility to the drive shaft in a vehicle. It is the coupling joint between the transmission and the differential. The U-joint acts much like a wrist in its sphere of movement. It is shaped like a plus sign (+) with a bearing cap on each end. The bearing caps contain small, thin roller bearings covered in grease. Most universals have a grease fitting in the center. Racing applications do not have a grease fitting because they are solid for additional strength. U-joints are also available to connect two dissimilar applications such as a Chevy driveshaft to a Ford differential.
Block the front wheels to keep the vehicle from rolling. Use whatever is available in the front and rear of one of the front wheels. Make sure the vehicle is on level ground to prevent fluid loss from the transmission.
Place the floor jack under the rear differential and raise the vehicle. Place jack stands under the axle on both sides of the differential. Lower the vehicle so it rests on the stands. Place the drain pan under the tail housing of the transmission.
Remove the four bolts or nuts securing the driveshaft to the rear differential yoke using a wrench. The U-joint on the rear of the drive shaft is secured to the differential yoke in one of two ways: It will have two bolts running through each strap around the U-joint bearings and is threaded directly into the differential yoke. The second method involves using U-bolts that are pushed over the U-joint bearing and through holes in the yoke secured with a nut on the backside of the yoke.
Grab the driveshaft and push it slightly toward the transmission to remove it from the grooves in the yoke and lower the rear of the driveshaft below the yoke. Pull the driveshaft straight back out of the transmission.
Manipulate the front and rear universals in a circular motion and feel for ease of movement and smoothness. If you feel any resistance, grinding, binding or looseness, the universal joint is bad. Remove a bearing cap on each universal and inspect it for grease and visibly worn roller bearings. If any wear is present or the cap has looseness, replace the joint.
Install the driveshaft in the tailshaft of the transmission first. Push it all the way into the transmission and lift the tail end of the driveshaft to match the differential yoke. Pull the driveshaft rearward to seat the universal joint into the differential yoke.
Install the universal bolts or nuts and tighten them with a wrench. Lower the vehicle and check and fill the transmission as necessary to bring it up to the full mark, if any fluid was lost through this procedure.
