Repairing a leather seam on leather seats is a difficult task, but it is not impossible. If there are large stitching rips it is necessary to use a leather sewing machine to repair the damage. However, small seam rips may be repaired by hand. The important thing to remember when repairing leather seams is to take your time and do the job right. A rushed job will tear the leather and make it necessary to replace the entire seat.
Remove the leather upholstery from the seat. The easiest way to do this is to remove any brads or staples holding the leather down on the bottom of the seats with a flathead screwdriver. You may have to make a few small cuts in the leather if it does not come off in one large piece, such as around seat belts if the leather seats come from a car. If necessary, use a seam ripper to rip out the leather seams to make removal easier. Try to remove as few seams as possible.
Mark the pieces as you remove them from the seat, writing which seam goes where. For example, put an "A" on two pieces that go together.
Line the pieces wrong side out together. Hold the seams in place with masking tape one at a time.
Sew the piece together with the leather sewing machine, needle and polyester thread. Do not use cotton thread as it can break easily and will rot over time. Sew each seam with a double layer of thread to make the seam strong.
Replace the leather cover over the seat. Stretch the bottom of the leather so that it reaches under the seat. Use the staple gun to staple the bottom of the leather to the seat. If brads were originally use to hold the seat in place, reuse them if possible for a neater appearance.
For small seam rips you can make the repair by hand. Thread a leather needle with polyester thread. Sew the seam together using an overhand stitch. Start the needle inside the hole. Pull it through so that the knot is invisible. Push the needle through the right and left sides of the thread and pull tight. Start again from the right side and pull through. Continue until the ripped seam is completely sealed. Sew a little beyond the base of the rip to strengthen the bond between the two seams.