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.
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.
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.
4. 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.