Studs often get damaged from overtightening or from cross threading a nut on the threads. A damaged stud is replaced by unscrewing it from the part and installing a new one of the exact same size.
Stud replacement can be difficult because the stud has often been in place for a long period of time. There has been constant heating and cooling, corrosion, and rust buildup between the stud threads and the internal threads of the part. These factors combine to make some studs very difficult to remove.
The first step in stud removal is to use penetrating fluid to remove the corrosion to free the stud from its mating threads. Soak the area of the threads with penetrating fluid. Allowing the fluid to soak into the threads overnight will make it easier to remove the stud.
Before removing the old stud, measure the distance it sticks up from the surface. This measurement will be needed later when installing the new stud. Use a 6-inch scale to measure from the part surface to the top of the stud. Write the measurement down so it can be referred to later.
A stud remove is used to remove studs. It is installed over the stud. The jaws on the stud remover grip the outside of the stud. A wrench fits on the stud remover and allows the technician to rotate the stud in a counterclockwise direction to remove the stud.
If a stud remover is not available, a stud can be removed with two nuts. Locate two nuts that are the correct thread size. To thread onto the stud. Start one nut and thread it all the way down to the bottom of the stud. This nut will be the drive nut. Start another nut and thread it down until it contacts the first nut. This is called the jam nut.
Put a wrench on the bottom drive nut and hold it in place. Put another wrench on the jam nut and tighten, or "jam" it against the drive nut. The jam nut will now hold the drive nut in position on the stud.
Now put an open-end wrench on the bottom drive nut. Turn the nut in a counterclockwise direction. Turning the nut in this direction causes it to want to unscrew the stud. Instead the forces cause the stud to unscrew.
When the old stud is out, inspect the internal thread. If it appears rusty or damaged, clean up the thread by running the correct size tap through the threads as previously explained. Compare the new stud with the old one. The studs should be exactly the same thread size and the same length.
Check the vehicle's service manual to determine if the threads of the new stud should be coated. If the stud should be locked in place and not easily removed, you may need to use a threadlocking compound or threadsealing compound. Threadlocking compounds are on studs and other fasteners when vibration might cause them to unscrew. Thread sealants are used when a stud extends where liquids, such as oil or coolant, could get on the fastener.
Antiseize compound is used on the stud threads to prevent the stud from reacting with the metal on the internal threads. If this happens, the stud could stick or seize. Antiseize compound prevents this reaction and makes the stud easier to remove the next time.
After the new stud is properly coated, it can be installed. Start the stud by hand, making sure it enters the threads securely. Turn the stud in as far as possible by hand before using any tools. Then use two nuts as described earlier to drive the stud into the part. Use the depth measurement made on the old stud to be sure it is driven in the correct depth.