To repair a steel brake line, you need a tubing cutter, an 11-millimeter flare-nut wrench, a 7-millimeter open-end wrench, a 3/16-inch steel brake line with metric threaded fittings and "bubble flare" ends, and a 3/16-inch compression fitting, as well as a 32-ounce can of brake fluid, a sturdy jerk and some jack stands. The repair process involves removing the rusty or broken section of the steel line, then splicing a new brake line section into the original brake line.
Before repairing your car's steel brake line, make sure you have the appropriate style and an adequate size of your replacement brake line. Most American cars use the "double flare" style of brake line.
Loosen the rear lug nuts, and jack the car up so the rear tire is elevated off the ground. Remove the tire. Use the flare-nut wrench to uncoil the brake line fitting until it is freed from the wheel cylinder.
Use the tubing cutter to cut off the rusty or broken section of the brake line. Step on the brake pedal a few times to expel any metal particles out of the line. Imitate the length and form of the removed section with the replacement brake line. Screw the "bubble flare" end of the replacement directly into the wheel cylinder.
Use a compression fitting to splice the old, unbroken line and the replacement line together. Make sure the compression nuts are tightened sufficiently.
Bleed the brakes to expel any air that has entered the system. Have an assistant step on the brake pedal so you can check for leaks.