How to Replace Brake Lines

Brake hoses and lines are filled with incompressible brake fluid. They convey pressure from the master cylinder to the cylinders at the wheels, engaging the brakes at the wheels when the brake pedal is pushed down. Leakage in any part of this system, shown by a decreasing level of fluid in the brake cylinder, requires immediate brake line repair.

Flexible brake hoses are often called part of the brake line. Here, “brake line” refers only to the rigid tubing that makes up most of the system, which is the most challenging to replace. 

This guide assumes that you are cutting, flaring, and bending your own brake line. If you have bought pre-flared, pre-bent replacement brake lines compatible with your car, you can skip some of the steps. 

New Tools Make the Job Easier

A new generation of brake line tools has made the entire brake line repair process easier and more reliable. Tube cutters ensure a clean and level cut, while double flaring tools make a precise double flare that holds pressure. Brake bending tools easily make tight bends exactly where you need them.

In addition to the tools, you will need to buy enough tubing to replace the existing brake lines. The tubing can be made either of several possible types of steel or a copper alloy, which is a bit easier to work with.

You should also buy replacement fittings suitable for your car. You can reuse the original fittings, but this isn’t always a great idea. They can be corroded, cracked, or have damaged threads.

Finally, you need enough replacement brake fluid to refill your system.

If you’re embarking on this project, give yourself a good three to four hours — a morning or an afternoon — particularly if you’ve never done it before.

Remove the Old Brake Line

  1. Jack up the car and support it securely at all four corners on jack stands.
  2. There is likely a lot of corrosion and dirt, so wear goggles to keep debris out of your eyes. Put a basin or rag under where you’ll be working. Brake fluid is corrosive and can damage paint, so wipe it up immediately if it spills.
  3. Removing the tire nearest to where you are doing your line replacement makes things easier. Unscrew the brake line from the fitting at the brake caliper. It is almost certainly corroded, so squirt some penetrating oil into it and let it sit for a while first. 
  4. If there’s a clip, pull it out with pliers.
  5. Do the same at the fitting at the master cylinder.
  6. Find and remove any other clips holding the line in place in between those points.
  7. Remove the brake line.

Prepare the New Brake Line

  1. Measure the old brake line’s length precisely with a length of string, carefully following each bend. Each flare will use up another quarter inch.
  2. Use a brake line cutter to cut the new line to the necessary length.
  3. Place the new or reused fitting over the end of the tube before flaring.
  4. Follow the flaring tool instructions to clamp the line, attach the yoke tool, and work the adapter into the line. The result will be a double flare that will form a tight seal once installed.
  5. Lay the new line down next to the old one. Using the tube bender, start at one end and match each bend in the new line to the old precisely, comparing the bends frequently. An error in bending steel tubing cannot be corrected without compromising the strength of the tube. A copper line can be bent by hand, and a bending mistake can be repaired by bending it back.

Install the New Brake Line

  1. Making sure you are attaching the right end of the line, attach the fitting to the brake caliper and hand-tighten carefully to ensure you are threading it properly.
  2. Reinstall the supporting bracket clips to hold the line up.
  3. Attach the other end of the line to the brake cylinder end, again hand tightening.
  4. Go back and fully tighten all the connections.

Checking Brake Hoses

If there are leaks in the hoses as well, they can be replaced by a similar process. However, replacing them doesn’t require anything but a pair of wrenches and some pliers by way of tools.

Bleeding the Brakes

Unlike brake fluid, air is compressible, and this process has inevitably introduced air into the system. Bleed the brakes before attempting to drive the car.

Many parts of modern cars have become electronic, or impossible for a home mechanic to work on. Brake lines are still satisfyingly physical, so with the right tools and equipment, you can perform all the needed maintenance and repair at home.

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