The brake lines on a vehicle are hard metal and encounter a lot of hazards being under the vehicle. When the brake lines are damaged or have aged to the point where they are leaking and require replacement, they must be replaced to prevent brake failure. A key component to the replacement of brake lines is taking the proper measurements. This requires more work than just a tape measure, as brake lines typically have a lot of kinks and bends throughout.
Raise the vehicle, using a floor jack, and secure it by placing jack stands beneath the vehicle and lowering it until only the stands are bearing the vehicle's weight.
Trace the brake line needing replacement until you find where it's connected to another brake line or component. This is your starting point. Place the end of the mechanic's wire at this point and tape it to the brake line, using masking tape.
Trace the brake line until you reach its end, attaching the mechanic's wire every six to eight inches on straight areas and every two to three inches on bends using masking tape. Tape the string at the end of the line and cut the mechanic's wire, using side cutters.
Remove the mechanic's wire from the brake line and lay it flat on the ground. Measure the mechanic's wire length using a tape measure and make a note of the length. To be safe, add approximately two inches to the length. You can always trim any excess line.
Close the micrometer jaws and press the "Reset" to calibrate it before measurement. Open the micrometer jaws and place them over the brake line.
Close the micrometer jaws over the line and read the measurement provided by the micrometer, this is the line's diameter.
