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How to Bend and Flare Brake Lines

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Tags: Tech, Tech, Brakes
Brake Lines

Having solid connections throughout your brake system is important for obvious reasons. Brake lines transfer fluid under a lot of pressure, sometimes 1200-1400psi, and leaking connections will decrease the brake line pressure and allow air into the system, which causes a spongy or low brake pedal. So to begin, we’ll show you some tips on how to plumb your brake system, get familiar with the various types of automotive flares, and look at some of the tools needed to get the job done.

Getting Started

For those designing the brake system from scratch, there are a few things to consider before getting started: the size and material of the lines, and the fitting style you will use to connect them. To keep your build simple, it’s recommended to use the same size brake lines for both the front and rear brakes. We suggest 3/16-inch line for most applications, although some rodders use 1/4-inch line. Speedway Motors offers 3/16-inch line in both standard steel and stainless steel for corrosion resistance and improved appearance. To ensure your brake system remains leak-proof, it’s best to choose one type of fitting and use it throughout with the least number of splices and fittings possible. Be sure to ask your Speedway Motors representative if you are unsure of the style of fittings you need with the brake parts you are ordering.

When you start designing the layout and determining where to route your lines, most of your bends will come off the master cylinder and around the front and rear axle. To make this step easy, first take a piece of baling wire and bend it to the length and shape you need and then use it as a template to form the brake lines. Doing this step first will save you the time and headache of tedious trial and error work.

If you have old lines that you're replacing, they can also serve as a template. In the below video, Tim uses this process to bend brake and fuel lines. It's also a great demonstration of the bending process and the tools required:

Common Types of Automotive Flares

In the automotive industry there are four main types of tubing flares: 45-degree double flare, 45-degree single flare, 37-degree single flare, and the bubble flare. The most common type of flare you’ll find on domestic and street rod applications is a 45-degree double flare. The double flare is used on high pressure circuits like the brake and clutch system. The tubing is folded over on itself, creating a thicker lip that makes a stronger seat surface for the flare nut to tighten against. A 45-degree single flare has the same 45-degree taper without the folded lip portion and it’s usually used for systems that require less fluid pressure like carbureted fuel lines.

A 37-degree single flare is typically used with stainless steel brake lines where AN-type fittings are needed. AN (Army Navy) fittings were a military standard and are now used on race cars and many street rods. By design, AN fittings cannot be interchangeable with any other type of fitting. The last type of flare is most commonly referred to as the bubble flare, but can be referred to as ISO, DIN, or Metric-style flare. The bubble flare is usually found on European imports, and towards the late 1980 started becoming more popular on domestic applications.

Tools of the Trade

Getting a good cut on your brake tubing is the first step in making a smooth and even flare. Hack saws or cut off wheels leave burs or uneven edges, which is impossible to mold into a flare that will seal. Tools like Speedway’s tubing cutter are ideal for any brake or aluminum fuel line.

One tool you’ve probably seen in almost every tool box is the wing nut-style flaring tool. These tools work great, they are compact and get the job done with ease, but if efficiency is something you're after, you might consider the deluxe flaring tool. The wing nut flaring tools are available in 45-degree double, single, and 37-degree flare. For stainless steel tubing, Speedway offers a 37-degree ratcheting-style flaring tool that is the best we’ve found for the money.

For the hobbyist or anyone working on the brake system frequently, the deluxe lever action flaring tool is by far the most efficient tool on the market. It has a rotating head that will form a 45-degree double flare or single flare, and bubble flares on stainless or mild steel tubing. Simply mount the head in a vise, pick out the corresponding die, set the rotating head to the needed position and pull the lever. It will flare 3/16 to 3/8-inch tubing perfect and fast every time. Check out the video below to see it in action:

While the deluxe lever action tool is by far the best option, good flares can still be made with the old fashioned wing nut-style tool. Below is a step by step guide to making a 45 degree double flare using one of these tools:

45-Degree Double Flare

The first step to achieve a good flare is making an even cut. Put a dab of oil on your cutting blade, this is a good way to ensure long life with your cutting tool.

In this photo, you will notice after making our cut, the tubing has compressed in on itself (closing the hole) unevenly which will not allow for an even flare. Before you flare the line, make sure you clean up the edges with a file.

You can take a cone file and carefully smooth-out any burs or uneven metal on the inside bore of the brake tubing. Skipping this step can split or crack the line when you attempt to make your flare.

Here is the final piece after filing both the inside and outside edges of the line. The most important part to a good flare is having a smooth and even sufarce to compress.

Insert the tubing into the flaring tool and use the bottom lip of the die as a guide as shown. The tubing should come up far enough to touch the bottom lip of the die about 1/4-inch.

Install the 45-degree double flaring die (included with flaring tool kit) and tighten down with a wrench until the die is flush with the top of the flaring clamp.

After the first flare is done, check to make sure the tubing has compressed evenly.

Next, remove the die and recompress the line with the flaring cone. Be careful not to over-flare the tubing which can split the line.

Here is how your finished 45-degree double flare should look. Make sure the tapered seat is smooth and free of burs for a tight seal.

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