When a zipper breaks on a pair of jeans, it can be difficult to repair the zipper. Most often, it is best to replace the zipper altogether. You can get the supplies you need at a local craft store. Use caution when choosing the size and color of the zipper. You want to match it as closely as possible to the one that is broken.
Assess the situation and make the repair
Check the zipper to see how badly it is broken and how difficult it will be to remove. Most often, zippers on jeans are very difficult to repair. It is usually easier to replace the zipper.
Use the seam ripper to carefully rip the threads that hold the zipper in place. Use caution so that you do not rip out the thread that holds the jeans together. Most often the thread that holds the zipper in place is a different color from the rest of the thread used to put the jeans together.
Use the scissors to cut the zipper from the jeans in the areas where you cannot use the seam ripper. Try to stay as close as possible to the seam as this will make the rest of the job much easier. Once the zipper is removed, check to make certain that the front of the jeans is intact and that the threads are in place. You will need to make repairs to the threads holding the jeans together if you have accidentally cut or ripped them when taking the zipper out.
Take the new zipper and measure it against the old one. Once you have the correct size measured out, you will need to put a bar tack in. This is just a few stitches at the bottom of the zipper to prevent the zipper pull from coming off. You can do this by hand or with a sewing machine. The strongest stitch to use is a zigzag stitch. Once you have completed the bar tack, cut off the excess part of the zipper.
Fold over the top flap of the zipper and secure it into place on the jeans with pins. Use the sewing machine to stitch the side of the zipper in place. Make two or three passes with the sewing machine to securely fasten the zipper in place. After the side of the zipper is in place, sew the bottom of the zipper in place by hand. You can also do another bar tack with your needle and thread, giving the zipper extra strength to stay in place. Finish off by doing the same for the other side of the zipper.