Tips and Tricks to Flare your own brake lines

 How a brake system works and is sealed.

The brake system in a modern car is very complex, but when you break it all down they all work the same. The simplest description is that the brake pedal is depressed which compresses a piston in the master cylinder creating hydraulic pressure that sends fluid to each corner of the vehicle and activating the brakes. The system MUST be air tight and free of any contaminates or air bubbles. The sealed connection at each brake fitting is made by tightening a brake line and fitting into an opening that is shaped the opposite of the flare. Once tightened, an air and fluid tight connection is made.

brakelineloopThe basic types of brake line fittings.

All Automotive fittings are “45 degree” fittings. The head of the flare is made at a 45 degree angle. AN or army/navy fittings are always a 37 degree fitting. They CAN NOT be interchanged.

1. Single Flares are only acceptable on low-pressure lines, but not acceptable for high-pressure brake systems. A single flare is just as it sounds, the line is flared out just once in a conical shape. Single flares are not acceptable for brake lines and tend to crack and leak quite easily.

2. A double flare is one of the most common flares found on vehicles. With these flares you’re forming the end of the line twice, actually folding the lip of the single flare over. It looks similar to a single flare but it is much stronger and acceptable for the high pressure found in a brake system. Double flares are found on most all US manufactured cars through the 80’s.

3. DIN/ISO or “Bubble Flares” are common on many import vehicles especially European vehicles. The flare is essentially the “first step” on the way to making a double flare. Although they’re similar, you should never interchange double flare and bubble flare parts. Most auto manufacturers started switching over to bubble flares in the 80’s.

The Common Types of Brake Flaring Tools

There are a many different flaring tools on the market. They all basically do the same thing, but each one has its place or reason to use it. Some are easier to use and require less of a learning curve and leave less room for error. Below are the most common used in both professional and DIY jobs.

wingnutflare hydroflare proflare

1. The basic “wingnut” style single/double flare tool is one of the oldest and most common flare tools on the market. They’re cheap, small in size, and can be used on the car. Forming flares with this tool requires multiple steps and moving parts. These can be extremely difficult to get perfect flares from every time. They are cumbersome to use and not compatible with stainless lines.

2. The Universal hydraulic flaring tool can be used on the car and requires little effort to make flares. Once assembled, they’re a single handed tool. These can do the largest selection of flares which includes, all 45 degree automotive flares and some GM PTC fittings. These are expensive with numerous dies and parts to interchange.  Because of the hydraulic advantage of this tool it can be easy to “overflare” lines. These do not work well on stainless lines.

3. Eastwood Pro Flaring Tool is a moderately priced, turret or “turntable” style tool with removable head and dies. This tool is simple to use, makes perfect flares every time with little to no room for error, and it can flare stainless. The design of this tool requires no changing of parts or resetting the brake line during the flaring process like other tools. The pro flaring tool is to only be used in a vice, and is very difficult to use off the bench or on a car. It does the 3 most common flares (single, double, bubble/DIN) but can make 37 degree AN flares with the add-on die kit

Common errors when making brake lines and how to correct them.

Even though it seems like flaring brake lines can be a pretty simple process, there are a number of small things that can cause a flare to be formed incorrectly and leak.

1. Cutting the line unevenly is probably one of the biggest errors made when making brake lines. It’s important that you use a sharp tubing cutter to cut brake lines. Using a cut off grinder, hacksaw, etc can be tough to make straight cuts and in turn causes inconsistent flares.

2. Freshly cut lines and brand new brake lines can have burrs or cutting debris on or in the line before forming a flare. This causes the excess material to be forced into the flare during the forming process and causes an inconsistent flare that could leak. We suggest to always deburr your lines with a file (found on the end of some tubing cutters) and clean your lines with Aerosol Injection to assure you have a clean line before you flare it. Applying spray lube to the end of the line can also help the flare form easier.

3. Too much “stick out” of the brake line from the die causes an over-flared or buckled flare. The line should be flush with the edge of the die to make the flare. Use “operation 0” on a pro flaring tool to set the correct stick-out of the line.

How to form lines correctly

Once you have all of your lines flared you will next need to route and connect the lines to the vehicle. Since brake fittings are usually in tight areas, bends need to be made in a line to get a brake line to fit and clear everything on the car.


1. Use Eastwood Tubing bender and Forming pliers to make smooth, accurate bends in brake lines. Brake lines need to have smooth, kink-free curves to avoid blockage of the brake fluid.

2. Exhaust tubing, sockets, cans, etc  can be used as forms to make smooth bends not handled by traditional brake tubing benders.

3. Forming pliers can be used to “tweak” the lines so they properly seat into a wheel cylinder or caliper.

 Additional Tips and Products

1. Always route your lines out of the way of jack points, high temp areas, or spots where suspension movement occurs. Attach to the vehicle every couple feet.

2. Use TIG filler wire or metal hangers unbent to make patterns for the shapes you need.

3. Always purchase quality brake lines and fittings that meet or exceed OEM quality. Copper brake lines are not advised, but Copper-Nickel hybrid lines are available that won’t corrode and will bend easier than mild or stainless steel lines.

brakegray4. Use Brake Gray to paint any parts that will or could be exposed to brake fluid. Parts coated with brake gray will withstand direct exposure to brake fluid and is a must on master cylinders, calipers,wheel cylinders, etc.

5. Always bleed the brake system after replacing a line or part of the system. Use the Eastwood Brake Bleeder Kit to remove any old fluid or air from the system.

brakebleederIf you use these steps you can save money on buying pre-bent kits and labor to pay someone else to make custom formed and lines for your vehicle and put it into more tools for your shop!



  1. I just purchased the turret style double flare tool also and am doing all new brake lines on my 63 Ford Galaxie 500. I did notice however, that the dies were installed on the turret and were not corresponding with the top of the turret showing the steps and sizes. Before I move these around properly, will this void my warranty?

  2. That’s very odd, first time I’ve heard that! They thread out, so that is no problem to swap them around. If you have any issues or further questions feel free to email our tech department directly:

  3. Not to be picky but …….when pressing the brake pedal you don’t “send” fluid to each wheel. What actually happens is you “move” the fluid as it already in every line and component of the hydraulic system….just saying.

  4. Very helpful, but info have a question? How can one tell what flares they need? For example my master cylinder is from a 69 corvette non -power disc brakes. My rear axle from strange engineering has braided line on it. Then there’s the front disc on my 80 camaro. It currently has no brake lines and I need to make new ones.

  5. Usually you can look at the socket or fitting that you do have and compare them with photos of each which can be found online. The sockets/flares are obviously different once you see them side by side. Hope that helps!

  6. Ok, I have the good vise mounted Eastwood flaring tool! I am trying to do 37 degree flares! I split the ends every time! I have double annealed 304 stainless, .028 thick straight from summit! I have tried this tool 20 times and every flare has at least one crack in it? Yes I lube up the end, yes I debur, and clean it well! Who here is using this tool for stainless brake lines and 37 double flare and it is working, can you give me some help? Thanks

  7. I’m having the same trouble. I’m finding that the vacuum is taking the past of least resistance, which is pulling air in around the bleeder screw threads, instead of pulling fluid from the master cylinder. What I do is use the mityvac to get as much fluid in the system as possible. Sometimes that is enough to get the system to a point where you can gravity bleed it.

  8. Nuts! I had never done a brake flare before or even seen one made. I followed the instructions carefully. I made two bad flares, both obvious immediately. Otherwise I did a complete custom set of brake lines for a ’65 Malibu that work perfectly and with no leaks. If you can’t follow instructions, hire a professional.

  9. I bought the Eastwood flaring tool and it broke on the first time. Eastwood exchanged it no charge & the replacement works great. The first tool must have had a casting flaw. Eastwood has been a great company to buy from. Thanks again Eastwood!

  10. Had a guy way back in the eighties when I was in the tool business, was doing a restore on an English car that had the bubble flare lines and he asked me if I had a tool to make those flares. I looked at the flare and immediately reconized it as the first step in the double flaring process and advised him about the tool to use and he told me that, that wouldn’t work. By reading your article I see that I was correct. Knew it all along, but it pays to always be attentive and learn something new. I have both the wing nut and pro style flaring tool(another make purchased back in the mid seventies) and both will work well if used properly.

  11. A big problem with the wingnut type is over-compressing the double flare. The edge should be round. If it appears sharp, you’ve crushed it and it’s little better than a single flare.

  12. The hydraulic flaring tool (#2) in your article can also make fuel line flares and power steering line flares…. useful when oem replacement lines are unavailable.

  13. The Hydra-Flare is an extremely versatile tool. There are usually a couple online merchants that have em on sale. 45° Brake line only is 71300 the Universal set is 71475.
    The universal set is only missing the 3/8″ GM transmission push fit dies and the 37° flare set. Fairly easy to purchase both if you need em.
    Don’t mash the flare tool pump handle when you’re finishing the double crimp. If you take it easy it’ll make excellent flares with very little effort. I took a piece of brake line and made 4 or 5 flares to get a feel for the force needed. Never needed to make more test pieces after that.

  14. I usually like to try and do things myself, nut I think this is one job I would leave to the professionals. I wouldn’t want to mess up and have the brakes fail when I am on the road. It was interesting to learn more about how the system works. I especially like your tip to protect any parts that will be exposed to break fluid. Will the fluid damage other parts of the car?

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