After a few years of use the springs in the bottom of a car seat can become worn, bent, damaged and even broken. If this occurs in your car, it is not necessary to completely replace the seat. It is possible to repair the broken springs to make them strong enough to function properly once more. This repair method is best for one to three broken springs, rather than multiple springs broken in the same seat. If more springs are broken, it would make sense to replace the entire seat.
Remove the seat from the car by loosening the bolts holding the seat to the floor of the car with the ratchet set or a wrench. Remove the seat and turn it upside down. Locate the damaged spring or springs.
Tear away any material covering the bottom of the seat to reveal the springs hiding underneath. You may have to remove batting as well. If the springs are bent rather than cut, cut the spring with wire cutters at the bent location and rebend with pliers to match the shape of the other springs on the bottom of the seat.
Cut off the threaded side of the drill bit. Use the reamer to drill out the inside of the bit to make it hollow. Drill out just enough from the middle of the drill bit for it to fit over the broken ends of the springs. You will probably have to try to fit the drill bit over the spring wire several times before you get the fit right.
Slip the broken ends of the wire into the two sides of the hollowed drill bit. Solder the spring to the drill bit with the soldering iron.
Wrap some safety wire around the entire spring several times. This will help stabilise the spring and prevent it from breaking the soldered seal. Hold the safety wire and the drill bit in place with duct tape.
Replace the fabric backing over the bottom of the car seat by stapling the fabric in place around the edges of the seat. Return the seat back to the car and connect all bolts. Don't forget to reattach safety belts and other accessories that belong with the seat.