The Double-Flared Brake Line

The Double-Flared Brake Line

The right way is the only way when it comes to braking safety
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The double-flare hydraulic-line fitting is undoubtedly the most common type of connection used in automobile braking systems today, followed by the bubble flare found on many European vehicles. Compared to single-flare connections sometimes used on fuel or coolant lines, the double flare is more substantial structurally and can withstand far greater operating pressures. Where the do-it-yourself enthusiast is concerned, double-flaring tools are more expensive than single-flaring devices and can be difficult to use. Your braking system is not something to take lightly, however, so do whatever it takes to get the job done right.

Cut to Length

Sections of straight, pre-flared brake line are available at nearly any automotive store, but unfortunately they aren't always the exact length you need for your project. The trick is to buy a section slightly longer than you need, bend as necessary, then cut off the end with the excess using a small tubing cutter. Unlike a hacksaw, a tubing cutter will create the perfect ninety-degree angle you need for a clean flare. Neatly dress the edge of the cut with a small file to ensure there are no burrs.

The Bubble

Slide your threaded brake fitting onto the tubing and insert the plain end of the line into the flaring device, being sure that you have the recommended length of tubing protruding from the clamping blocks. Tighten the clamping mechanism well, as the initial flaring operation will try to shove the tubing through the tool. As the handle is turned and the die compresses the exposed tubing, a bubble will form under the die. If the tubing crinkles or is bent off center, you will have to cut off the damaged portion and try again.

The Double Flare

Depending on your flaring tool, remove or rotate the bubble-forming die away from the newly formed bubble. Lower the cone shaped die against the bubble and slowly compress until the upper half of the bubble is flat against the bottom. Retract the die and inspect the flare for gouges or protrusions that could create a leakage path. If the flare looks good in the tool, remove the line and inspect the outside of the flare for any signs of damage. Slide the threaded fitting up to the flare and check the fit. Assuming everything looks good, install the line on your vehicle, bleed the brakes, apply pressure to the brake pedal and check for leakage.

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