The U-joint of a car are designed to move the engine power and torque out of the transmission unit and into the wheels during the working of the suspension. The suspension moves up and down, and the U-joint (or universal joint) allows the driveshaft to spin despite this movement. The U-joint is in fact involved in moving and maintaining the power of the entire driveshaft: however due to the stresses and strains of this, the U-joint can become worn out and damaged.
The U-joint consists of an X shaped cross, which is the part spinning round the driveshaft, held onto the yoke by four pins: these pins, or caps, have tiny bearings like needles inside, and are covered with grease. The needle-like bearings are the points most likely to wear out: you will be able to hear rattling when the car is in gear, or a loud vibration. This is the time to replace the U-joint. It is not difficult to replace the U-joint, and it can be done in a day.
Step 1 - Preparing the Car
You will need to place the car up on a car jack, so that you can reach the drive shaft comfortably. Ensure the car is properly supported on the jacks, and never undertake this work when you are alone. Once under the car, it is a good idea to drain the transmission fluid (this can be put back or replaced later).
Step 2 - Removing the Driveshaft
Using the wrench, take off the driveshaft with the U-joint still in position. Take it to a workbench or a table inside, after covering the surface with newspaper or protective sheets. Make sure that you mark the assembly before removing, so that you can put it all back in the same position, preserving the balance of the driveshaft.
Step 3 - Removing the U-Joint
Take the retaining pins off of the U-joint's caps. As U-joints generally have new pins, you do not need to worry about replacing them: so take them off quickly with pliers or wire cutters. Turn the U-joint around on the yoke, and then push the cap and cross through so that the opposite cap can be taken off. Remove the cap from the yoke, and repeat.
Step 4 - Remove the U-joint from the Front of the Yoke
Once all of the caps are freed, it should be a simple matter of removing the U-joint from the driveshaft. If you find it a bit difficult, then pliers or a wrench can be used to force the U-joint away from the yoke.
Step 5 - Getting the U-Joint Off
In some cars, the U-joint is actually pinned to the yoke with a nylon ring. To get rid of this ring, you will need an additional tool called a ball joint press. Once the caps are removed, place the yoke in the press and tighten until you hear a 'pop': this is the sound of the nylon ring snapping. The press will probably be quite difficult to move, but once this ring is broken, the U-joint will be easy to remove.