OEM brake tubing in the US have what is called a 45° double flare at the ends which means the end of the tubing is folded in on itself and flare at 45°. A flare nut then crushes the tube end against the mating surface to make seal. After the flare has been crushed it will require more torque to seal seal each time the system is disassembled and reassembled as well as the potential for fatigue cracks to form where the metal has been folded over. This is fine for the commuter-consumer they aren’t going to be swapping out components from week to week or season to season. Racers tend to tinker with their cars and may have to dismantle everything or replace components frequently so they need components that are designed to be disassembled and reassembled multiple times. The 37° AN flare is a single flare is backed up by a tube sleeve that is held to the mating part with a nut and is capable of being disassembled multiple times without fatiguing and since it’s a single flare its actually easier to make than a double flare. Additionally this method is rated at higher pressures and is held to a higher standard so the system is more robust and can endure the extremes of racing. It is fairly common for a race team to immediately replace all stock brake lines with the 37° AN flared tubing as part of prepping the car for racing.
The down side of the AN flare is that the components are much more expensive and they also require an adapter to connect them to the stock brake components such as the master cylinder, proportioning valves and ABS block. Also the tools tend to be more expensive but you can find a 37° flare tool on Summitracing.com for about $30 HERE. If you decide to upgrade your brakes to the AN fittings then you can save yourself some money and time by only replacing the lines that run from the ABS block (or the proportioning valves for those cars without ABS) to the calipers and leave any plumbing that might be going from the master cylinder to portioning valves or ABS block. The AN fittings can also be used for routing fuel, vacuum lines, and various other fluids. Make sure to use STEEL fittings on the brakes or any other high pressure hydraulic systems and you can use aluminum fittings for anything else.
It is pretty easy to convert to AN flared lines but there are a few more parts you need to buy. I would suggest getting stainless tubing and an appropriate tubing cutter because the $5 Acme Autoparts special will just cry when you try and cut a stainless line with them; they are barely adequate to cut a regular steel line. Try this one from Mcmaster-Carr: part number 2764A14. I haven't use this particular one but it does say its for stainless and titanium.
Step 1: Cut the stainless tubing to length and deburr the ends. PUT THE HARDWARE ON THE TUBE! Easy to forget this step you get so excited about flaring the brake line and forget to put the hardware on. So put on a TUBE NUT, then a TUBE SLEEVE. Make sure they are facing the right direction. See pictures at bottom.
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| 3/16" Stainless Brake Line Cut and Deburred. |
Step 2: Clamp the tube into the flaring tool. It should be sticking a little above the surface of the tool. The one pictured below is from Summit Racing. You can find it HERE.
Make sure you clamp this down TIGHT. If its not tight enough the tube will just slide out. I used a wrench as shown below to get it extra tight.
Step 3: Flare it!
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| Successful 37 Degree Flare |
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In a very simple brake system, with just two cylinders and a disc brake the cylinders could be connected via tubes, with a piston inside the cylinders.
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