Do you live in a place like Michigan where road salt treats your car like a school of piranhas treats a wounded duckling? If so, your brake lines might be rusty, so you should replace them to avoid things like death, despair and turmoil. It’s actually a cheap and easy job; here’s how you do it.

I’ve been working on my $600 Moab Jeep for months now, trying to get it ready for the inevitable shit-show that will be the 1,600 mile road trip from Michigan to Utah. It’s been a grueling wrenching experience filled with setback after setback, as rust turned the car into a tetanus-filled rust trap nightmare.

But one obstacle that I thought would surely be a major time-suck—my rusty, crusty and perhaps even musty brake lines—actually ended up being 1,000 times easier to mend than expected.


It also helped that I had Opponaut Santiago has successfully Sno*Drifted by my side making sure I didn’t do anything completely idiotic (a tall task).

Here’s how we swapped my iron oxide brake lines for nice, shiny steel ones.

1. Buy Or Rent Equipment


Once we determined that the old brake lines weren’t just covered in superficial rust, but that the scaling posed a real safety hazard that could send me flying off a cliff, it was time to wrangle up some hardware.

The equipment we needed for the job was:

Standard brake line sizes are 3/16-inch, 1/4-inch, 5/16-inch, 3/8-inch, 1/2-inch, 4.75mm, 6mm, 8mm and 10mm. Of those, 3/16-inch (about the same as 4.75mm) is probably the most common, and that’s what we ended up using.


But if you don’t know what size your line is, either measure it with a caliper go online to find the answer in some informative automotive content. Just remember: everything on the internet is always accurate.

You can buy brake line in rolls. At my local O’Reilly Auto Parts store, they charge about a dollar per foot, and we only needed about 13. You can also rent brake flaring kits, like the one shown above free of charge, though it’s worth noting that different cars have fittings for different kinds of flares.


The most common type of flare on modern American cars is the double flare, though some European cars, especially older ones, use a bubble flare.

If the flaring kit doesn’t come with a brake cutting tool, just buy one. They’re less than 10 bucks. You’ll need this because if you try to cut a brake line with a shear, you’ll just squeeze the end shut. You can use a box cutter for deburring, and you can buy fittings for a couple bucks at your local auto parts store.

In the end, you could probably manage to replace your entire brake line for about $20. Yes, it’s amazingly cheap, and even better: it’s amazingly easy.


2. Remove The Old Brake Line

My old brake line was really, really nasty. The whole thing was covered in scaly rusty, and as soon as we bent one section, it broke off and leaked everywhere.


When you undo the brake line from the junction at the master cylinder or at any other fitting, be sure to hit the nut it with some penetrating lubricant (PB Blaster is your friend), and if necessary, apply heat.

The last thing you want is rounded off fittings (though if you do round them off, use vice grips to loosen them). My go-to brake line removal method involves hitting the fitting with PB Blaster, applying heat with a torch, and hammering on the end of a flare nut wrench to apply an impulse load.


A note on flare nut wrenches: do not go cheap on these. If you buy a $3 flare nut wrench (also called a line wrench) at AutoZone, you can expect to round your nut off. Just get a nice, tight-fitting, wide wrench that makes lots of contact with the nut.

Once you’ve undone the brake line fittings from the junction and brake hoses, just yank it out.

3. Cut New Brake Line To Size


You’ll need a cutting tool to whittle the brake line down to size, using the old brake line as reference. If you just use a pair of snips, you’ll end up squeezing the end of the brake line, and you won’t be able to flare it.

So just buy one of these pizza cutter-like tools, tighten the cutting wheel against the brake line, and start spinning the tool around the line, gradually tightening the cutting wheel screw as you go.

After a minute or two, the wheel should cut through the line and you’ll be ready to start bending.


4. Deburr


After you’ve cut your line, you’re likely to have little metal burrs on the inside of the brake line, so take a sharp edge and clean those out. If you don’t properly deburr, your flaring tool won’t create a smooth sealing surface on the brake line.

5. Make Light Bends By Hand


Using the old brake line as reference, make some light bends in the brake line by hand. The line is fairly malleable, so you won’t break it or kink it as long as you keep your bends below about 45 degrees.

Keep in mind that you may want to make the bends once the line is installed in the car, as bends in the line can make routing the line a struggle.

6. Make Major Bends With A Pipe Bending Tool


Route the line into its approximate final location and use the brake bending tool for major bends like 90 degree-ers. Bending is fairly straightforward, as you’re essentially just wrapping a tube around a smooth filleted corner.

7. Insert Your Fitting


Once you’ve flared the line, the fitting isn’t going on, so be sure to put on your fitting before you flare. Remember that: fitting, then flare. Fitting, then flare. Fitting, then flare.

I could probably write that a million times, and you’d still forget. I know I will.

If you forget to put the fitting on before flaring, just cut the line down a bit and try again.


8. Make Your Flare

Making a flare is fairly simple. Simply insert the brake line into the appropriate hole in the vice. Choose the adapter for that size brake line, and use the thickness (or first step if it has two steps) of the base of the adapter (which Santiago is holding in his hand above) to determine how much the brake line should stick out from the vice.


Lay the adapter on its base right next to the brake line that’s jutting out of the vice and look at it from the side to make sure you’ve got it lined up.

Then tighten the nearest vice bolt all the way, squeezing the flaring bar halves together. On the other side, tighten the bolt snug, but not too tight. All you’re trying to do is make sure the grooves in the vice hold the brake line and prevent it from slipping axially.


Next, crank the yoke down until the adapter hits the vice and the yoke’s screw no longer wants to turn. Remove the adapter, and the end of your brake line should look a bit like a mushroom:


To finish off your double flare, cranking on the yoke again, this time without the adapter in place, as shown in the image below:

In reality, you’re more likely to be doing this under your car. You could flare the line before you install it, but your initial length estimate for the brake line should always be a bit on the long side, as it’s easier to cut the line down than to splice in a new line.


That’s what I did: I installed a little too much brake line, then I went underneath and cut it down to size and flared it from under the car. It’s not nearly as comfortable as doing the flare on your work bench, but wrenching and discomfort go together like manual transmissions and wagons.

The final product should look something like this:


Here’s my installed brake line. It’s not exactly pretty, as I intentionally put bends in the line to take up some of the slack. Still, the peace of mind I got for only about $20 and an hour of work was absolutely worth it.