In this tutorial I am going to show how to replace a zipper on jeans and pants with a fly. You can follow the same steps no matter if the fly is top stitched with one or two lines of stitching.
In this example we are working on a pair of pants with a fly. The attachment of the zipper is similar to the one on jeans. If you need to replace a zipper on jeans, you can follow the steps in this tutorial as they are the same I would follow when replacing a zipper on jeans.
Here are the written instructions. At the end of this post you are going to find the video tutorial as well.
Here are the steps to follow:
Remove the broken zipper
Start with removing the old zipper. Unpick all the stitches that hold the zipper at its place.
First, break some of the top stitching that goes over the zipper on the waistband. Once you release the zipper tape from the waistband on both sides, unpick the two curved vertical seams that go on one side of the front, over the zipper fly.
This opens the zipper fly and now you can see the joining seam on this side (image 1). Unpick that seam as well.
Then, remove the bar tack that fixes the fly over the zipper. Usually, there is another bar tack under the zipper teeth as well. You need to remove that one, too. This can be the slowest thing to do. I like to use the seam ripper for that, but a pair of clippers can do the job as well.
When you remove the zipper completely on that side, you are going to be able to open the zipper fly piece (image 2).
We need to break some of the top stitching on the other side of the waistband. The waistband usually goes all the way to the end. On this pair it doesn’t, but it doesn’t make such a difference. We still need to unpick a bit to release the zipper.
The truth is that in alterations on ready to wear clothing there will always be differences and challenges to overcome. So this pair here can actually be a good example on variety.
Unpick the topstitching on the other side of the zipper and detach the zipper from the separate under flap piece (image 3). Here is how this side of the jeans look when the zipper is removed (image 4).
Cleaning all the remaining threads and prepare to install the new zipper.
To match the fly size and sew the new zipper precisely, pick a zipper with the same length as the broken one. I couldn’t find the exact length and I had to shorten my new zipper to match the size of the old one.
If you need to do that as well, here is a video on how to shorten metal zippers.
If you want to know more about zippers, here is a post on types of zippers and how to use them.
Replace the zipper on jeans
Now, let’s start attaching the zipper. We reverse the steps we followed when unpicking.
Sew the zipper to the side with the under flap piece
Put the zipper foot and sew the zipper back to the under flap (images 5 and 6). I align the zipper tape to the edge of the under flap. You might use the edge of the under flap as a guide or even better - the line of the old stitching. Sew close to the teeth with the zipper foot.
Next, we need to topstitch on the same side. This topstitch serves as a joining seam as well. It attaches the under flap together with the zipper to the front (image 7).
Put the free end of the zipper tape under the waistband and sew close to the teeth with the zipper foot. My waistband doesn’t go all the way to the end, so I am starting from the top. You would most probably need to start under the waistband.
Here is how the zipper looks on this side when it's done (image 8).
Sew the zipper to the side with the fly
Next, we need to attach the zipper on the other side. First, we overlap the fly to find out where we need to put the other side of the zipper (image 9). It should overlap without twisting and pulling the fly. The button and the buttonhole should match as well.
Turn the pants inside out and moving the under flap out of the way (image 10). Pin the zipper to the fly. Pin only to the inner fly piece.
Check the position of the zipper once again, because this is how it is going to look when sewn (image 11). If you need to, make some adjustments so that the button and the buttonhole as well as the fly overlap nicely.
Then, change the position of the zipper foot so that it sews on the other side. Starting from the bottom, sew the zipper to the inner fly piece (image 12). Keep the under flap out of the way.
Working at the face side, pin the front to the fly piece (image 13). We are going to make these two curved seams at the front to fix the fly.
I am going to change the foot for the last time and use the regular foot for the rest of this sewing project. You can sew over the zipper, but still make sure to keep the under flap on the other side of the zipper away so you don’t accidently sew through it. (image 14).
I am going to make the two curved lines on the front, starting at the top. If you are working on pants or jeans with separate waistband, you should start at the top of the front of the pants, right under the waistband.
Use the old stitching line as a guide if it is still visible. If not, draw the line with some chalk. Sew all the way down until you reach the beginning of the curve (image 15). We are going to stop here with that line for now and make the second parallel line of stitching. Don’t forget to lock all stitches at both ends.
Now it’s time to finally fix the under flap peace in place. Put it under the zipper where it is supposed to be (image 16) and make the final curved stitches on the front. We need to sew on the front here so be careful not to displace the under flap piece.
Start where we ended the second line, lock the stitch and slowly finish the curve (image 17). Be careful to go under the zipper teeth so that you don't break a needle. Turn the pants around, make a couple of stitches straight up and continue with the first curved line.
Unfortunately, I am using a matching thread so it’s not very easy to see where I am sewing. I hope you can get the idea here. Match the beginning of the line and once again, lock the stitch.
The last thing we need to do is to restore the waistband stitches on both sides. Put the free end of the zipper tape under the waistband (image18) and make the seams (image 19). You would most probably need to go only horizontally here. I am going straight as well in result of the specific pattern.
As I always do when finishing an alteration, I am going to try the new zipper and see if it functions and looks well and I am done with replacing the zipper.
If you want to learn how to make all of the most common alterations on ready to wear clothing, here is an online course on Tailoring Ready-to-Wear.
Here is the video tutorial on how to replace a zipper on jeans.
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