I still remember the first time I had to put a double-flare on a hard steel line. My dad and I were doing a brake job on our 1987 Suburban. The rear hard line for the wheel cylinder had rusted up and the nut was stripped. We had no choice but to cut it off and make a new hard line. Having never done this before, we went to the parts store for some advice. They provided a double flaring tool and a piece of hard line to cut and bend to size. Cutting and bending the line was easy, but we had a heck of a time figuring out how to flare the line, as the kit did not come with instructions. That was 25 years ago, now I can make a double-flare in my sleep. It is not difficult, but if you have never done it before, it can seem like a bit of voodoo. There are several key points that you need to know before you get started, so get ready to learn how to make a double flare brake line.
There are three types of flaring tools: manual, hydraulic, and leverage manual. Most of the time you will be dealing with a manual tool, usually mounted in a vise.
Manual – This what you will be dealing with. These kits are inexpensive and readily available at any NAPA Auto Parts Store. These tools are clamped into a vise, and use dies and a threaded press to impart the flare.
There are two types of flares: 45-degree and 37-degree. 45-degree flares are the most common in automotive use. AN or Army-Navy fittings require 37-degree single flares. This 37-degree tool looks the same, but notice that it does not come with the dies.
Hydraulic – Hydraulic flaring tools are generally only used in shops where a lot of line flares are made on a regular basis, the average DIY mechanic does not need one.
Leveraged Manual – The leveraged manual flaring tool uses dies and a swing-arm to press the flares into the line much faster and easier than a basic manual kit. These often cost a few hundred dollars, and are excellent for the builder that needs to make many flared lines, such as when restoring a car.
How to Make a Double Flare
We will focus on how to use the manual flaring tool.
The first step is to cut the line. The end of the line must be clean and smooth. Some kits come with a tubing cutter, you need one regardless. Tubing cutters work best when the blade is tightened after every pass. You don’t want to load the brake line into the cutter and just crank down the cutting wheel.
Before placing the tubing into the flaring tool, the fitting must be slid onto the line. Don’t forget this, as you can’t install the fitting once the line is flared.
The flaring tool base is easiest to manage when secured in a vise, but can be used without a vise if necessary. The hard line should be loaded into the corresponding hole and the wing-nut clamps tighten enough to hold the line. Each tool comes with a set of dies. Each die is specific for a line. The die must match the line you are flaring. The die has a step, this is the depth of the line for the flare. Once this is set, the wing-nuts can be fully tightened.
Next, the die is inserted into the line with the stub sliding into the line itself.
The press locks over the base and the over the die. The press is threaded down until the die touches the base. This is the bubble portion of the flare.
The press is released and the die removed. The press replaced over the line and threaded into the line once again. You only need to thread it until the press is tight, you don’t want to crank it down.
The finished flare seats against the fitting and when installed, will provide the seal for the fluid.
Flaring lines is easy as long as you follow the instructions. Next time you need to replace a hard line on your vehicle, you can be proud that you made it yourself. Of course if you have any apprehensions, you can always check with your local NAPA AutoCare for assistance.
Check out all the brake system products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to make a double flare brake line, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.
A life-long gearhead, Jefferson Bryant spends more time in the shop than anywhere else. His career began in the car audio industry as a shop manager, eventually working his way into a position at Rockford Fosgate as a product designer. In 2003, he began writing tech articles for magazines, and has been working as an automotive journalist ever since. His work has been featured in Car Craft, Hot Rod, Rod & Custom, Truckin’, Mopar Muscle, and many more. Jefferson has also written 4 books and produced countless videos. Jefferson operates Red Dirt Rodz, his personal garage studio, where all of his magazine articles and tech videos are produced.