A combination of metal and flexible rubber brake lines carry brake fluid from the master cylinder to each wheel cylinder or caliper. Sometimes the lines travel through a proportioning block where the line pressure becomes equalised, then travels to the brake cylinders or calipers. Brake lines suffer impact breakage and corrosion over time and need to be replaced. Some occasions call for replacing just a section of brake line rather than the entire length. Joining two brake lines together with a new spliced section can be accomplished with a few speciality tools and some basic steps.
Set the shift selector in park or neutral, depending on your transmission type. Set the emergency brake firmly. Use a floor jack to raise the vehicle high enough to place two jack stands under the rear frame. Raise the front of the vehicle and place two jack stands under the front frame. Place a drain pan (or two) under the damaged section of brake line, where you intend to cut it. Unclasp the brake line from its plastic hangers, allowing enough line to drop a foot or more.
Place a pipe cutter around one section of the brake line and turn the knob clockwise. Rotate the cutter in a circle while you turn the cutter knob. Rotate the cutter enough to cut the line. Do the same on the other end of the line. Measure the damaged section of line with a tape measure and subtract 1/2-inch, for your replacement line length. Use a wire brush to clean the ends of the cut lines on the vehicle.
Sand the ends of the vehicle brake lines to a slight bevel with sandpaper. Curl the sandpaper to fit inside the brake line opening and sand any burs away. Do both lines. Push two male brake line fittings over each of the vehicle's brake lines with the threads pointing outward.
Place one vehicle brake line inside a flare tool block, setting the end of the line 1/4-inch out past the line socket. Tighten the tool block clamps by hand. Refer to the flare tool instructions for the proper flare angle and diameter for your brake line.
Place the flare tool hook clamps around the block and align the conical flare shaft inside the brake line. Twist the T-handle on the flare tool until the flare shaft compresses the end of the line into a mushroom shape. Remove the flare tool and repeat the same process on the other brake line.
Use a pipe cutter to cut your new brake line to your previous measurement, which was 1/4-inch shorter than the old brake line segment. Sand the inside and outside of the brake line end, removing any burs or plastic brake film. Slip two female connectors on each end of the new brake line, with the threads pointing outward. Set one end of the brake line inside the flare tool block, exposing 1/4-inch of line. Tighten the tool block clamps by hand.
Place the flare tool around the block, clamping the ends with the two hooks. Turn the flare tool shaft T-handle until the end of the brake line compresses into a mushroom flare. Repeat the same procedure on the other end of the brake line. Take the new brake line section underneath the vehicle.
Screw one male fitting from the vehicle line into one female fitting on the new line, by hand. Do the other side the same. If you need to, pull the vehicle brake line backward or forward to connect the threads -- they will slide in the hanger fittings. Tighten each fitting by using two opposing fuel line wrenches. Hold the female fitting still with a wrench while you tighten the male fitting clockwise. Tighten both fittings until firmly snug. Snap the brake line back up into the plastic hanger guides.
You will need to refill the master cylinder with the lost brake fluid and bleed the lines after the splicing procedure. Have an assistant pump up your brake pedal and hold it while you open a bleeder valve with a fuel line wrench to allow the escape of air. Shut the valve and have the assistant pump up the pedal and hold it again. Loosen the valve until a steady stream of brake fluid escapes, then shut the valve. Bleed all the wheel cylinders and calipers this way. Replace the brake fluid in the master cylinder.