I did a post some time ago about how to change a rear brake caliper on a small sedan. Around the same time, I had to a brake line repair on the work truck I was using. Line repairs tend to be pretty common here in the Northeast, and likely in other areas that salt the roads in the winter.
Being able to make your own brake lines can save you a ton of money. It is dirty, difficult work most of the time, which is why the shops will charge you so much to do it. The actual parts and tools involved, however, are fairly inexpensive. Flaring kits like the one pictured below have been readily available for under $20 for decades. I paid around $18 for this one about 25 years ago. These cheaper kits have some flaws, and may only last for a few a jobs out of the box (I had to replace the 'clamping' bolts on this one, and it has worked great ever since), but at over $100 for any line repair at the mechanic, it can save a lot of money in a couple jobs. As you can see, you can flare several sizes of line with this kit, although I have only ever used the smallest three sizes for brake lines. The larger ones fit some power steering and fuel lines that I've seen, and even a couple hydraulic lines on heavy equipment, but it won't always be strong enough to actually flare those lines. Most newer lines in these larger sizes will use a different style of connection than this anyway. It will work for flaring copper lines used on some propane and natural gas connections.
This post will deal specifically with enameled steel brake lines, but the process will be the same no matter what kind of metal the line is made of. The first thing to remember, especially if it's the last connection on the line, is to put the 'nut' (I don't know if there's a special term for this kind, probably) on the line. For most brakes jobs, you will be able to re-use the old ones if you are careful removing them, and I highly recommend this. New ones are usually just a few bucks each or less, but sizing them properly can be a bit of a task if your local auto parts store clerk doesn't know their business well. If you don't remember to put the nut on first, you will have to cut your beautiful flare off and start over.
The 'die' part of the tool (probably the right word) should have a little ridge on it that you use to set how much of the line sticks through the 'vise' part of the tool. This height is a little different for each size of line, and needs to be set as close as you can get it. I like to roll it all the way around the end of the line, to make sure the end is square. If not, I'll use a file to square it up.
When tightening up the vise, always start at the end closest to your line. This lets you take advantage of leverage when tightening down the other end. If you do this backwards, you will have to use a LOT of force tightening down the second wing nut. The tool comes with a small bar that you can insert between the wings for extra leverage. For this smallest line, I don't need it to get things clamped all the way down.
When the line is clamped properly, the two parts of the vise should be touching in the middle. If it isn't clamped tight enough, the following steps will just push the line out of the vise. For the first flare, or single flare, you insert the post end of the die into the clamped end of the line.
The kits come with a deburring tool that you use to clean any jagged edges off the inside of your line before inserting the die. There is a little resistance inserting the die sometimes, but it should go in fairly easily. If you need to hammer on it, something is wrong, and you should re-cut the end and start over.
The tool also comes with an 'anvil' that sets into the indent on top of the die and clamps onto the sides of the vise. Tighten this just finger tight at first, and make sure everything is lined up just right. Give it a few wiggles while tightening it up, and when nothing moves anymore it should be ready to flare.
The same handle that you use to tighten the wing nuts on the vise inserts into the top of the anvil so you can tighten it down until the die seats against the vise. This can take a lot of force, especially with larger lines. It help if you keep the threads on the anvil lubricated, and will also help your tool last longer. Additionally, it makes it easier to 'feel' when the die has seated while you're tightening the anvil.
Once the die has seated, unscrew the anvil and remove the die from the line. You now have a single flare, which I haven't seen on any vehicle brakes since the 80's, but I do still see these used on some power steering lines. If you're not sure which type you need, I would try the double flare first.
To double check that the flare set completely, look at the back side of the vise. If the line was pushed out, you will see bright streaks here where the metal scraped against the 'teeth' inside the vice.
To set the double flare, simply insert the anvil back into the single flare, without the die. For this part, being able to feel when the anvil seats is much more important. You'll feel a consistent resistance from the time it starts pushing into the flare until all the metal has pushed to outside of the bevel at the top of the hole your line is clamped into. At this point, the resistance will increase significantly, and you'll want to stop. If you overtighten, you can squish the flare out of shape and it will leak.
That's all there is to it! Remove the anvil, unclamp the vise, and your shiny new brake line is ready to install. This type of standard enameled steel brake line is usually sold in spools of 50' for around $25. This is usually much better line than the short sections of pre-flared brake line that they sell at auto repair stores, and will typically outlast them by years. 50' will be enough to replace every line on most cars twice, or more.
The teeth of the vice will leave some marks where they bite in. I like to put anti-seize compound on these, it helps keep the line from rusting in these spots where the enamel is worn off and helps keep the line from seizing fast to the inside of the nut, so it will be easier to remove if you need to pull the same line a couple years later.
The nut should slide easily up against the flare and turn freely. Sometimes bits of enamel or slivers of metal cut loose by the vise teeth will get between the line and the nut, stopping it from moving freely. If this happens, you should back the nut off and clean things up. Your line may still install and seal properly, but the line will likely rub through and leak inside the nut at the site of contamination in a short time.
Of course, once you have the tools and know how to do it, this is the easy part of brake line repair. Getting the old line out, and getting the new line bent into the proper shape and put into place is usually the worst part of the job. Sometimes, getting the new line into place is so difficult that I have to install it before both ends are flared, and then flare one end in place, usually in a wheel well or under the hood near the master cylinder. Under the hood tends to be easier.
I hope this post taught you something, or saved you some money, or at least helped you negotiate with your mechanic! Remember that nothing is as hard as you think it is, and I hope to see you back for more!