How to Repair a Brake Line

Brake line in car.
Peter Schinkel/Flickr/CC-BY-2.0

When you have trouble keeping your car's brake fluid levels up where they need to be, there is a good chance that one or more of the brake lines has developed a leak and is allowing hydraulic brake fluid to leak out of the system. When this happens, the brakes will initially feel spongy, they may stop working altogether. Failing brakes indicate a serious situation that needs to be dealt with immediately. 

While a leak is possible anywhere along the hydraulic brake lines running to the master cylinder to the individual brake piston housing on the wheels,  it is most common at the flexible portion of the lines that run from the brake's piston housing to the rigid the rigid piping that continues on to the master cylinder. Because these flex tubes are exposed to the road and move with the wheels move as the car is steered, it's not uncommon for these lines to get brittle and develop cracks.

This article will discuss the replacement of the flex hose portion of the brake line that joins directly to the brake's piston housing. Make sure to buy a replacement brake hose that matches your car's specifications. Most mechanics will replace the brakes lines on both wheels at the same time since if one line is bad, it's likely the other one may go bad soon. 

Materials You'll Need

  • Brake fluid
  • New flexible brake lines
  • Screwdriver (if needed)
  • Open-end wrenches
  • Rags
  • Jack stands
  • Tire lug wrench
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Remove the Old Brake Line

Loosen the brake line connection.
Use two wrenches to loosen the brake line. photo by matt wright, 2007
  1. Place your car on jack stands or jack up the car, then remove the wheel. 
  2. Identify the rubber or steel mesh flex line that runs from the brake unit's piston housing to the rigid metal portion of the brake line. 
  3. If there is a retainer clip on the hose at the fitting locations, remove it with a screwdriver.
  4. Normally, the connection points each consist of two halves joined with hex-shaped fittings. Position a rag beneath the fitting to catch the brake fluid as it drains out.
  5. Use one open-end wrench on each half of the fitting, and twist them in opposite directions to free the fitting. 
  6. If the hose is anchored at some point in the center to a strut of other fixed point, detach this connection.
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Install the New Brake Line

Fit the new brake line in place.
The fittings on the new brake line. photo by Matt Wright, 2007

Installing the new brake line is really just a matter of reversing the process used for removal. 

  1. If there is a retainer clip on the new hose, attach this to the piston fitting.
  2. Carefully hand thread the connection together, by hand. 
  3. Once it's hand tight, use two open-end wrenches to tighten the fitting securely. 
  4. If there is a fixed mounting bracket that secures the hose to a strut or other fixed point, make this attachment to finish the installation. 
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Add Brake Fluid and Bleeding the Lines

Your new brake line.
New brake line installed. photo by Matt Wright, 2007

With the new brake line installed, you'll need to add brake fluid to the system and bleed the brakes of air that is in the lines. 

  1. Open up the bleeder cap on the brake caliper or wheel cylinder
  2. Have a helper pump the brake petal to force the air out of the bleeder cap.
  3. Wait you see fluid coming out of the bleeder cap,  close the cap.