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How to fabricate steel brake lines

Our project Jeep needs a complete brake overhaul, that means 
making our own replacement steel brake lines

The brakes on our ongoing Jeep restoration, Project CJ3A, were a complete disaster. Virtually every part in the system needed replacement, including the steel lines. We could have purchased those lines already preformed, but the cost would have been much higher than buying the basic materials and fabricating our own. So, we spent extra time in the shop and saved a few dollars. Here’s what’s involved in making them.

The Jeep needs 3/16-inch mild steel brake lines, so we stopped at an auto parts store and picked up a full 25-foot roll along with the correct number of fittings. The total cost was about $50.

The tools

To turn that role of steel tubing into formed lines, we need to cut and bend the pieces into the correct shape. Then, a 45° double flare has to be put on each end. Doing that requires a few special tools. In true Grainews style, we’re going to stick with the basic, low-cost types for this job. We want to use tools anyone can justify adding to their roller chest.

This project calls for a special tubing bender, which costs about $15. Aside from that we needed a basic flaring tool kit that typically retails for $40 to $50. Other than that, only ordinary hand tools are required.

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Cutting and bending

When doing a project like this, keep the original lines — or what’s left of them — to use as patterns to fab up new ones. Measure the overall length of the originals and unroll that length of tubing from the roll. Cut it with the tubing cutter that comes with the flaring kit.

After cutting the pieces to length, ream out the resulting minor deformity on the ends. We used an ordinary step-style drill bit for that. Next, file a bevel onto the outside edge with a hand file. After that step it’s possible to get right to flaring the ends on the shorter pieces. But a couple of sections for the Jeep were too long to lock into the vice without standing on a step ladder to reach the end. With those, we went ahead and bent them to shape first, which made it easier to fit them into the vice.

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The tubing bender came in handy, but it can only make bends with one radius. In some places we wanted tighter curves, that meant improvising by locking two 3/8 bolts into the jaws of a bench vice. Sockets from a 3/8 drive could be slipped over one bolt to give us the radius we wanted. The other bolt acted as an anchor to force the bend.

We mostly used a socket for a 5/8 nut, which gave us a tight bend, but not so tight we risked kinking the line.

Flaring the ends

To put the 45° flare on each end, the first step is to make sure the cut ends are perfectly square. One easy way to do that is to put each end into the flaring vice upside down. When the tubing is locked into the flaring vice and protruding just slightly from the bottom, a hand file can be used to file it flush with the surface.

Then flip the vice over and insert the tubing into it the correct way. Let the tubing stick out exactly the same height as the shoulder on the appropriate flaring die. That ensures exactly the correct length of tubing will be bent over to form the double flare.

Forming the double flare is a two-stage process. First, the die is placed in the end of the tubing. It is forced down by the hand tool. Twist the tool until the die bottoms out on the vice. Then remove the die and twist the point of the hand tool down onto the tubing end. This folds over the single flare left by the die and creates the double flare. Don’t over torque the hand tool or it could compress the flare too much.

This sounds like a simple process, but with the kind of flaring kit we used, it can be challenging to get the flares correctly shaped. Both halves of the flaring vice need to be perfectly even. If they aren’t, the flare won’t be formed at 90° to the tube, and it might not seat properly. That means it will be a leaky line. It’s easier than you’d think to end up with a useless flare. Getting everything lined up correctly can sometimes be a slow, frustrating process.

Take your time at this stage or you’ll find yourself starting all over again.

If you forgot to slide both fittings onto the line before flaring both ends, you’ll be left with a useless piece of tubing and have no choice but to cut off a flare you just made. You can’t get them on if both ends are flared. And if you are putting small radius curves in the line, make sure the fittings are where they’re supposed to be or you won’t be able to slide them into place over a tight bend.

Before installing the line, use compressed air to blow out any metal filings from the cut that might contaminate the brake system.

Getting the fittings on the line to thread into place usually means tweaking the angle of the tubing a bit. Lubricate the fittings with a little brake fluid before threading them in. Never use any other type of lubricant, that could contaminate the brake fluid.

With the brake job out of the way and the Jeep now capable of stopping, the next thing we have to do is make it go.

About the author

Contributor

Scott Garvey

Scott Garvey is a freelance writer and video producer. He is also the former machinery editor at Grainews.

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