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Brake Line Double Flares

Alright, so today on Repairs101 I thought I’d show you the procedure for making standard double flares using double wall steel tubing. We’re going to make some brake lines. Stick around.


OK, so you know the first thing I gotta say is that your brakes are the most important system on your vehicle. You know, it doesn’t have to start and it doesn’t have to turn. It doesn’t have to have a kick adze stereo. It just needs to be able to stop.

So you need to be absolutely sure that you’re using the correct type of fitting. The correct type of line and the correct type of fluid, for that matter. If you don’t know what kind of fluid to use look in your vehicle’s owner’s manual. Or sometimes the information will be right there on the cap of the master cylinder, under the hood.

OK well it would be fair to ask: first of all what does a single flare look like? OK so here’s a single flare with the flare nut on it. To give you an idea of what that looks like. As you can see the flare on the tubing matches the flare on the fitting and they lock together. Perfectly good fitting for low pressure but not for high pressure applications.

Double flares

So you can buy your brake lines ready made at your local auto supplies store. They’ll come with the flare nut on them and the standard double flares already installed for you there.

So what I’ve done here is I’ve taken a standard piece of double wall and cut it in section and polished it up with a diamond file so that we could see how it’s folded over onto itself and that’s what’s meant by the double flares. You can see how it’s curled back inside. So in fact it has two sealing surfaces now, the inside edge here as well as the face of it here. And it’s a lot less likely to crack on the radius, which is a common problem for single flares.

So you’ll need a double flaring tool kit. I got this nice Blue-Point set from my Snap-on dealer. OK so I’ve got his little tubing cutter alright? In the idler there are these notches cut into the idler rollers. And what they’re for is so you can load your flare right into that notch on the followers and now the cutter is just going to take off the very end of it. And that’s so you can just remove the flare if you want. OK so I’ve removed the single flare alone just by running it through that little groove on the followers.

Prep the end

OK so after you’ve cut it there’s three things you need to do to prepare the end. First of which is you need to cut a chamfer on the edge here. So you’re either going to do that using a flat file  or you’re going to use your bench grinder.

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OK so I generally like to mount my flaring bar right into my vise just to hold things steady but you can actually do this pretty much freehand if you need to. Flip the flaring bar over, take my piece of three sixteenths. You can see at this end I’ve already created a nice flare.

So now at this end, before I go any further I’m going to drop one on that way and the other one on the opposite way – you see how they’re going to both work: this one is going to work for this end, and this guy’s going to work for this end.

OK so I put those on and I open it up and I put it in just proud, just barely. I’m going to do that down this side then this side. Every time, always going to do the side that the tube is on first, and then the far side. I’ll take my flat file, and just make sure it’s got a nice flat top on it. And then I’m going to take my reaming tool. OK it has been well prepared by chamfering the edge, levelling the top and reaming out the inside.

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Alright so now I’m going to flip it back over to the correct way. Again, make sure that I’ve got my flare nuts in place and in the right place opposite the end over here.

Flaring bar

Going to put it in the three sixteenths loosely, just holding until I grab the three sixteenths anvil and I’m going to put that beside it and match the height.

Alright so you set the protrusion of your tube from your flaring bar to the same height as the shoulder. Here on the anvil that is the correct size. In this case it’s three sixteenths of an inch. OK when you see that you’ve got the height right you’re going to tighten the side that’s closest. Then the other side. Make sure the bar’s nice and square, that it’s lined up flat.

The only thing you want to lubricate your brake system with is brake fluid. So I keep a little DOT3 brake fluid in here. I’m just going to use a little drop of DOT3… well a couple of drops.

So you’ve got them set up to be the same height. And then you’re just going to drop the anvil in there. Check that it’s the right height. Drop it in. Fit the yoke with the flaring cone over the anvil. Get it so that it’s nice and straight, and then turn it down by hand. Then turn the flaring cone down on the anvil. Turn the flaring cone down onto the anvil until the anvil is flush with the flaring bar.

Hand tight

So now we’re going to put the flaring cone directly into the end of the tube. And turn that down until it’s flush. It goes fairly easily, you don’t need to use big heavy wrenches or anything to get this done. And then it’s done. That’s what it will look like. I’m just going to clean that up with a little brake cleaner and some compressed air.

I’ll undo this. Get that free. As you can see I’ve got my flare nut on the end. And there’s the finished product, double flared with the flare nut on it. That’s a standard double flare.

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