This small pipe cutter from Harbor Freight is a nice size to cut tubing in hard-to-reach places. You tighten the adjustment knob, spin the tool around the tubing a couple times, tighten, spin, tighten, spin, and, voila, you have just cut your brake lines.

If you are building your own track car or hot rod, eventually you will probably find yourself dealing with hydraulic lines. These pesky lines always seem to be in the way of something else you are working on and they generally have pretty important things inside them, like fuel or brake fluid. Keeping the hard lines in the car is a good thing because they don’t expand under pressure like a rubber line. So, if you want to modify the car, then you may need to bend your own hydraulic lines and double-flare them for a good seal. The process is relatively easy and inexpensive.

The basic tools you will need, a pipe cutter and a double-flaring tool, are available at any local hardware store. Brake lines and tube nuts can be sourced at your favorite automotive retailer. For less than $50, you can have everything you need to create your own lines. We wanted to make a set of brake lines when we deleted a stock proportioning valve, which didn’t provide enough rear brake bias, on our Honda Challenge project car. We replaced the stock proportioning valve with a Wilwood adjustable unit from I/O Port Racing Supplies, which the driver can adjust while on track. This required running new brake lines from the proportioning valve to the rear brakes.

The whole point of all of this brake line double-flaring was to install a proportioning valve sourced from I/O Port Racing Supplies. This way we can adjust the car’s brake bias during a race. A better-balanced braking system allows you to go deeper, and everybody knows deeper is better.
The whole point of all of this brake line double-flaring was to install a proportioning valve sourced from I/O Port Racing Supplies. This way we can adjust the car’s brake bias during a race. A better-balanced braking system allows you to go deeper, and everybody knows deeper is better.

The first step — if you’re smart — is to drain the brake fluid before you do anything else. If you are dumb — like we were — you just cut the brake lines with the pipe cutter and drain the brake fluid as it leaks all over your hands and the interior of the car. Brake fluid will stop leaking when the master cylinder is empty.

The real trick to double-flaring brake lines is all about the order of operations: First cut; second, install flare nut; third, complete the initial flare with an insert; fourth, do the secondary flare without insert; and fifth, bend the line. The order is important because the tube nuts will only slide onto an unflared, unbent line. So you need to remember to slide the tube nut on —in the correct direction — prior to flaring or bending the line. Did we forget to follow this order correctly when we did our project? Yes, multiple times.

Once the tubing cutter has been used, you should have a cleanly sliced metal tube ready to use a double flaring tool to ensure your hydraulic fittings don’t leak. If there is any residual hanging metal from the cut clean it up prior to flaring the line.
Once the tubing cutter has been used, you should have a cleanly sliced metal tube ready to use a double flaring tool to ensure your hydraulic fittings don’t leak. If there is any residual hanging metal from the cut clean it up prior to flaring the line.
The most important thing to remember before double-flaring your brake line is to slide the tube nut on the line first, threaded side out. The tube nut will not go on the line once it has been flared.
The most important thing to remember before double-flaring your brake line is to slide the tube nut on the line first, threaded side out. The tube nut will not go on the line once it has been flared.

The good news is brake line is cheap, so picking up another few feet of it isn’t a big hit on your wallet. When using the flare tool, it is critical that you use the correct diameter on the tool for the diameter of the tubing. The length of the tubing that should stick out in the flaring tool can be measured by the thickness of the correlating flaring insert tool (see photos).

To know how much tubing to leave outside of the flaring tool prior to flaring the line, just use the depth of the appropriately sized insert as your guide. In this photo you can see we have the 3/16-inch line flaring fitting lined up with the tubing. Perfect length.
To know how much tubing to leave outside of the flaring tool prior to flaring the line, just use the depth of the appropriately sized insert as your guide. In this photo you can see we have the 3/16-inch line flaring fitting lined up with the tubing. Perfect length.

We were working with 3/16-inch brake lines, which is a standard automotive diameter, and used the 3/16 settings on the double-flaring tool. The first flare, using the insert tool, rolls the tubing edge inward. Once that is complete you remove the insert and then use the pointed portion of the tool to flare the tubing outward. It is important that you use a double flaring tool for hydraulic brake lines because a single flare will not be strong enough for the pressures of an automotive braking system. Brakes are not something to mess around with. If your braking system fails, you will have to use something else to slow you down … like a wall. That is not what you are looking for. It’s much easier to flare lines correctly than it is to replace frame rails.

This is a double-flaring tool. Here I would recommend spending a little more money because the inexpensive Harbor Freight version caused me to have some double flares that leaked. I upgraded to a Craftsman tool for $45 and have been happy with the results.
This is a double-flaring tool. Here I would recommend spending a little more money because the inexpensive Harbor Freight version caused me to have some double flares that leaked. I upgraded to a Craftsman tool for $45 and have been happy with the results.

Once you have your double flare, the next trick is to bend the line so it will align with the rest of the braking system components. Again the order here is important. The tube nuts need to be placed on the line where they will be once the system is completed. If you make a bend in the line between the tube nut and the double flare, the tube nut will not slide into the correct position. If you do this, you will be starting over from step one, making another trip to AutoZone, and there will be plenty of cursing involved.

Bending hydraulic line is easy to do, but there is a bit of art to it. Using a small tubing bender will ensure you don’t crimp the line, but the benders are not intuitive as to where the radius of your curve will begin or end. There is some finger crossing and hoping for the best when you bend these lines. Making mistakes and then trying to bend the line back straight to redo the bend results in pretty rough-looking warped lines. They will still work, but your friends will ask you if you were drunk when you did the project. If you had the guts to cut into your braking system, there is good chance you were actually drunk, but let’s get back on topic.

When you tighten your tube nuts into a proportioning valve or a tee, loosen and tighten them a few times to help the newly flared line seat into the correlating female end. This will help prevent leaks. Don’t go gorilla-tight on this stuff because the tube nuts are made of brass and will strip. Once your new line is in place, bleed your brakes and check for leaks. Then check for leaks again. Then check for leaks again. You don’t want leaks. Did I mention the need to check for leaks? Yes? Then check for leaks.

Once you have the flaring tool lined up correctly, all that is left to do is tighten things down and let the tool flare the brake line. Pro tip: use a screwdriver between the wing nuts to help you get some leverage as you tighten the tool over the tubing. If it isn’t super tight, the flaring tool just pushes the tubing out the other side.
Once you have the flaring tool lined up correctly, all that is left to do is tighten things down and let the tool flare the brake line. Pro tip: use a screwdriver between the wing nuts to help you get some leverage as you tighten the tool over the tubing. If it isn’t super tight, the flaring tool just pushes the tubing out the other side.

Building your own hydraulic lines is easy and inexpensive. Nothing about it requires a degree in engineering or expensive tools. Ignorance and beer will provide you with enough courage to cut your system open. Some patience and finesse will help your project go back together smoothly, along with some spare parts for redoing the line — three times. Good luck!

After the first flare has been made with the line insert, the second time the tool is used is when the pointed fitting is tightened into the line creating the larger diameter. These steps must be done in the correct order, or you will be doing it again.
After the first flare has been made with the line insert, the second time the tool is used is when the pointed fitting is tightened into the line creating the larger diameter. These steps must be done in the correct order, or you will be doing it again.
We used a brass tee to split the line coming from the adjustable proportioning valve to both rear brakes. It is critical that the interior of the tee is designed for a flared tube to seat. Otherwise you will have puddles of brake fluid everywhere and no brakes, which is a bad thing.
We used a brass tee to split the line coming from the adjustable proportioning valve to both rear brakes. It is critical that the interior of the tee is designed for a flared tube to seat. Otherwise you will have puddles of brake fluid everywhere and no brakes, which is a bad thing.
This simple and inexpensive tubing bender can be used to correctly bend your lines and ensure they don’t crimp, which could cause hydraulic flow issues. It takes a few practice tries to make sure you are bending the tube exactly where you want it, but practice makes perfect.
This simple and inexpensive tubing bender can be used to correctly bend your lines and ensure they don’t crimp, which could cause hydraulic flow issues. It takes a few practice tries to make sure you are bending the tube exactly where you want it, but practice makes perfect.
Here is everything you need to make your own brake lines: tube nuts, a double-flaring tool, some tubing benders, and a small pipe cutter. And you will want some towels because you are going to make a mess with your brake fluid, which is very corrosive to paint.
Here is everything you need to make your own brake lines: tube nuts, a double-flaring tool, some tubing benders, and a small pipe cutter. And you will want some towels because you are going to make a mess with your brake fluid, which is very corrosive to paint.
When done correctly, creating your own brake lines can look pretty legit. The tubing bender made building this line easy to create, with the bends in the perfect locations.
When done correctly, creating your own brake lines can look pretty legit. The tubing bender made building this line easy to create, with the bends in the perfect locations.
If you are building a line that isn’t already installed in a vehicle, placing the double flaring tool in a vice makes things easier. Pro tip: you can see the tube nuts are already on the line. This is important because the nuts have to be in the correct position prior to bending the lines or double flaring the lines.
If you are building a line that isn’t already installed in a vehicle, placing the double flaring tool in a vice makes things easier. Pro tip: you can see the tube nuts are already on the line. This is important because the nuts have to be in the correct position prior to bending the lines or double flaring the lines.
If everything goes as planned, this is your finished product: a tube nut on the brake line next to a double-flared portion of the tubing. All that is left to do now is to tighten it into a fitting and begin to bleed your brakes.
If everything goes as planned, this is your finished product: a tube nut on the brake line next to a double-flared portion of the tubing. All that is left to do now is to tighten it into a fitting and begin to bleed your brakes.

To read more from Rob Krider, or to contact him, go to www.robkrider.com.

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Image courtesy of Rob Krider