The Process Behind Flaring a Brake Line

Flaring a brake line isn’t as hard as it looks, but there are plenty of steps that you have to learn to do the job properly. A good double flare will help seal your brake line and give your system the strength it needs to stop again and again. A poor double flare will leak and will keep your vehicle from braking properly. That’s why it’s so important to take the time to learn to do it right. The following double flare brake line instructions will help you learn the whole process properly. Follow along and make sure you know what you’re doing before you try it yourself.

Choosing the Line

The brake line you choose is pretty important. You have three main options to pick from, copper brake line, steel and stainless steel. Copper and stainless steel are about the same price, but copper is significantly easier to work with. It’s softer and will flare with lower-quality equipment. Stainless steel is the most durable but it’s brittle and very hard, meaning you pretty much need pneumatic equipment to flare the line properly. Steel brake line is about half the cost of the other two options, but it doesn’t last as long as they do. It’s harder than copper, but a decent quality flaring tool (link to inline page) will handle it without an issue.

Preparing the Line

One of the most important steps to properly flaring a brake line is the preparation. If you don’t prepare the line properly it simply isn’t going to flare like it should. It’s vital that you take the time to chamfer the outside and inside of the line end. That means to cut away a tiny section of the line at a 45 degree angle to give it a bit of a beveled edge. To do this you should carefully grind away some of the line using a file or a dremel bit. During my brake line project I liked using my Dremel with a few bits to do this job.

This wheel grinder bit works well for chamfering the outside of the line, and this cone-shaped grinding bit works well for the inside of the line. Spin up the wheel and move it around the outside of the line with it at an angle to create a nice chamfer. Stick the tip of the grinding cone right in the line and spin it at a medium speed to chamfer the inside and you’re done.

If you decide to go with files this process will take a bit longer. You can do the outside with full-sized files, but you’ll need something smaller for the inside. I started with a set of tiny diamond files, but it’s a pain to do it this way.

If there are any double flare brake line instructions that you follow, it should be these prep steps. If you do them properly you’ll be in much better shape when it comes to actually flaring the lines.

Flare Nuts in Place

Now that you have your line prepped, it’s time to slide the flare nuts in place. Put two of them onto your line. Set them so the threads are facing out toward the end of the line, you want the threads facing in opposite directions outward. Make sure you put the nuts in place before you start flaring your line, or you could end up with a line you can’t attach!

Insert the Brake Line

With the flare nuts in place you can insert the brake line into your flaring tool. This step is the same no matter if you are using an in-line tool or one of the bar-style tools for flaring a brake line. Slide the brake line through the proper section of the flaring bar or the square flaring clamp depending on your kit. Your want the line sticking out the same amount as the ledge on your adapter.

When it’s sticking out the proper amount lock it in place using the clamps or the hex key adjustments on the side.

Completing the Flare

Apply a couple drops of brake fluid to the flaring cone and the little adapter of the proper size for your line diameter. Now set the small tip of the adapter into the brake line itself. The rest of the instructions depend on the kit that you’re using.

Bar and Clamp Flaring

With the adapter in place carefully lock the yoke assembly onto the bar of the tool and insert the bar so that you can twist it down to apply pressure. Twist the cone down onto your adapter to press it all the way down flush against the bar tool. Now loosen it up and remove the adapter from the brake line. Finish the double flare by twisting the lubricated cone down into the brake line itself just enough to flare it out.

Congrats you just completed your first double flare!

Don’t be discouraged if it’s a bit uneven, when you use the bar and clamp style units there is a chance of making a lopsided double flare. Practice several times and you’ll get the hang of it over time.

In-Line Flaring

Since you sprung for the in-line tool finishing your flare will be simple. Twist the large threaded fitting down over your square clamp with the adapter inserted. Now simply thread the cone down into the threaded fitting to apply pressure to the adapter down below. Fit a socket over the end of the cone piece to tighten it down all the way. Loosen the cone piece, unscrew the threaded fitting and remove the adapter. Put the fitting back in place and screw down the cone piece into the empty brake line to complete your flare. Once you feel pressure only go a single turn or two to create a nice flare.

Making double flare brake lines isn’t too difficult, but you have to follow all these steps to do it properly. You’ll probably mess up the first few times and that’s okay. Take your time and burn through a bit of brake line until you feel like you have the process mastered. Brake lines are cheap, but you’ll waste a bunch of time installing lines that aren’t made properly. Once you’re confident about flaring a brake line you can replace lines as needed on your vehicle and save a bundle.