Everything You Need To Know About How To Flare A Brake Line

To flare a brake line, you’ll need a flaring tool kit and a good deal of automotive expertise. Here’s how to do it.
Written by Patrick Price
Reviewed by Melanie Reiff
Brake flaring (the process of seamlessly merging two sections of stainless steel brake line) can be accomplished using a flare tool. This greatly reduces the risk that the brake line will snap—but it should only be attempted if you’re certain that you know how to do it. 
You’ll probably never need to flare your brake lines using a double flare tool since all cars are legally required to have double flare brake lines, to begin with. If you’re doing some DIY work on your brake system, however, you may need to know how to use a brake line flaring tool on a brake hose to create a hard line. 
It’s important that you properly flare your brake lines using a double flare, as failure to do so could lead to a fatal brake line malfunction—not to mention, you could face criminal charges! 
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What does it mean to flare brake lines?

In a hydraulic brake system—the most common type of automotive braking—the high pressure required to stop your car is provided by hydraulic brake fluid. This fluid is stored in your car’s master cylinder. When you press on the brake pedal, the fluid is carried to your brake calipers through the brake lines, which are typically made of stainless steel. 
If the brake lines snap or develop a leak, the resulting brake failure could be fatal. To prevent this car manufacturers use a technique called brake flaring. Flared brakes are extremely resistant to leaks and are unlikely to break. 
But what does it actually mean to flare your brake lines? A flared line is a type of fluid transfer hose where each end of the tubing is stretched out. This allows each end of the line to fit seamlessly together with another section of brake tubing—or with a different part of the brake system. It’s the same technique that sailors have used for centuries to strengthen bowlines. 
You’ll find the flaring technique used on fluid lines throughout your car. Your fuel lines, for instance, use flared tubing. However, while some fluid lines are only single flared, all brake lines are required by law to be double flared. If you have a car that was manufactured in Europe, the brake system might use another type of flare called a “bubble flare”, which is similar in durability to a double flare. 

Types of brake line fittings

If you’re replacing a section of brake line for the first time, you’ll need to purchase a hydraulic flaring tool. You’ll also need to make sure that you check your brake line fittings and that you get the appropriate type of brake pipe/brake tubing. 
Several different specifications need to match up for a section of brake line to be compatible with your car’s brake system. Make sure that each of the following types of brake line fittings is a match for your car:
  • Material. Brake lines are typically made of braided stainless steel, but some are made of rubber.
  • Diameter. To avoid using an adapter, make sure that you get a replacement line with the same interior diameter as your current brake hose. Most brake lines are either ⅛ inch or ⅜ inch in diameter.  
  • Thread size. For a new section of brake hose to fit properly, it will need to have the correct thread size for your brake system. Your owner’s manual should specify the correct thread size for your car. 
  • End configurations. The end configuration refers to the size and shape of your brake line endings. Most cars use ISO Flare, DIN Flare, or Double Flare end configurations. 
  • Fittings group. You’ll also need to make sure that you’re ordering brake lines with the fittings from the correct fittings group (male fittings, female fittings, center support fittings, or banjo fittings). 
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How to make a double flare? 

As mentioned above, you’ll likely never need to flare your own brake lines unless you’re doing a DIY brake line replacement. Because the consequences of improper brake maintenance are so dangerous, it’s best to have a professional work on your brake if you don’t have extensive experience in that area. 
If you are working on your own brakes, though, you’ll need to double flare all of your brake lines to avoid severe legal consequences and to ensure your safety. Here’s what you’ll need to do to make a double flare:
  • Step 1: Make sure that you have a double flaring tool and/or flaring kit. 
  • Step 2: Measure the length of brake line tubing that you will need and cut off an extra tubing using a hacksaw. Then, remove any resulting burrs. 
  • Step 3: Place the section of tubing into the flaring bar and clamp it down. 
  • Step 4: Use the flaring tool kit’s yoke to create a bell shape in the tubing. Then, feed the tubing into the bell shape to create the desired double flare. 

How to find cheap car insurance

Faulty brake lines are a serious hazard on the road. Thankfully, having double-flared brake lines greatly reduces the risk of brake failure. That said, however, there are countless other safety concerns for drivers and their cars—that’s why it’s so important to have reliable car insurance
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No—you absolutely cannot single-flare a brake line. Not only is doing so dangerous, but it’s also highly illegal. If you’re caught driving with single-flare brakes lines, you could face serious criminal charges. If you’re in an accident while driving with single flare brake lines, and the accident causes a fatality, you could be charged with manslaughter.
For automotivebrake lines, you want to flare at a 45-degree angle.
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