Rick's Free Auto Repair Advice

Fix a rusted brake line — 3 repair options

Learn the 3 options to fix a rusted brake line

Over time, steel brakes lines rust and leak. There are only 3 ways to fix a rusted brake line and there are pros and cons to each approach.

1) Buy a set of pre-bend brake lines (if they’re available for your vehicle) and install them in place of the rusted line, or
2) Buy a coil of copper/nickel brake line or long lengths of steel line and run new lines from the master cylinder to the brake, or
3) Splice in a new section using an automotive grade flare coupler

Option #1: Purchase pre-bent brake lines

Pre-bent brake lines or full kits are only available from the dealer or online. Most dealers have to special order the line. So both getting a replacement line means a delay while waiting for the part to arrive.

set of stainless steel pre bent brake lines

Pre-bent brake line kit

The advantage of buying a set of pre-bent brake lines

The pre-bent brake lines sold in kits are often made from stainless steel so they won’t rust like your factory brake lines. They’re pre-flared and they come with new brake fittings on each end of the line so you don’t have to search for the right fitting. If your brake lines run under the vehicle, chances are you can replace your rusted brake lines yourself just by unscrewing the old lines and installing the new pre-bent brake lines.

The disadvantages of pre-bent brake lines

In addition to the wait times, they’re also pricey. Expect to pay $200 to $350 for a set of pre-bent stainless steel brake lines. That may seem like a bargain compared to the typical shop charge of $1,000 or more to make new brake lines from scratch, but there’s a catch. They’re not always as easy to install as you think. For example, many rear factory brake lines run from the master cylinder, into the firewall, along the rocker panels inside the vehicle and then exit the interior near the back seat. There is no way you can replace one of those lines with a single pre-bent section. Plus, many car makers run the rear brake lines over the gas tank, so you still have to deal with lowering the tank to use a pre-bent line. In other words, that set of pre-bent brake lines may wind up costing you more than you think in labor if you don’t do the job yourself.

Option #2: Abandon the old brake line and run a new one

This method can be done right away and the parts are cheaper. But running a new brake line involves a lot of labor. You have to duplicate all the bends and flare the ends. On some vehicles, fixing a rusted brake line using this method can cost as much as $800 in labor.

Option #3: Splice in a replacement section

new subaru brake lines

Here’s an example showing of a Subaru splice block. Subaru ran a brake line from the master cylinder to the splice block at the rear of the vehicle. They then ran a smaller length of line from the block to the flex hose connector for the rear brakes.

Contrary to online folklore, it is not illegal to splice in a replacement section as long as you do it properly (more on that below).

In fact, carmakers routinely install small sections of brake line between the master cylinder and a splice block, and then a smaller section of line to the brake flexible hose connector (see the photo to the right).

To consider this option, you first have a good section of tubing on each side of the leak. Those sections must be clean and accessible.

To make the splice you’ll need an automotive grade (NOT plumbing grade) double flare coupler, corresponding brake line fittings, new line and a double flare tool.

See this post to learn about brake line flaring tools.

It IS illegal to use compression unions or single flare unions for brake line repairs

What you can’t do is use compression fittings or single flare plumbing unions to make a brake line splice. That’s not only bad practice, it’s just not safe. Compression fittings are designed for plumbing pressures around 40-psi, while brake lines must handle up to 2,000-psi. In other words, compression fittings can’t handle brake line pressure and can leak during heavy braking.

compression unions are illegal for brake line repairs

However, you can perform a brake line splice using an inverted double flare union and double flare fitting

As long as you use an automotive grade SAE double/inverted flare, SAE “bubble” flare or DIN Single Mushroom flare union with the appropriate size and type fitting, you can spice in a new section of brake line. But you should avoid these common DIY brake line repair mistakes:

brake line union

Common rusted brake line repair mistakes

• Using cheap flaring tools—Making a double/inverted or bubble flare requires high quality tools. If you think you can buy a cheap flaring tool and make good flares, take it from me, you’re kidding yourself. The clamps won’t hold tight and the forming tools won’t fit properly. You’ll wind up with lopsided flares.

This flare was made using the S.U.R.&R. PFT409 Piston Grip Flaring Tool Kit. To see how it’s done, click here

• Not practicing before starting the repair— Making high quality double/inverted or bubble flares takes practice. If you think you’re going to make a good flare on your first try, I promise you, your connections will leak and you’ll have to remake the entire line.

• Not having the proper bending tools—Most auto parts stores sell cheap bending tools. They work fine for large diameter bends. But you’ll need to make some sharp 90° bends and those cheap bending tools aren’t going to cut it. I’ve listed some bending tools below. Trust me, you’ll need them.

• Using steel brake line—Yes, that’s what they used at the factory. But steel brake line

S.U.R.&R. UltraBEND® brake line

S.U.R.&R. UltraBEND® Flexible Brake Line Tubing

is hard to bend and hard to flare out in the field. Do yourself a favor and buy a spool of copper/nickel easily bendable brake line. Not all auto parts stores carry it, but it’s worth finding because it’ll make the job MUCH easier. I like S.U.R&R because it bends easily without kinking and is much easier to flare than steel brake line. It costs a bit more than the copper/nickel other brands you can find online, but it’s also a much better product. The cheap stuff is made with thinner walls so it kinks easily. Find S.U.R&R UltraBEND® Flexible Brake Line Tubing at at many national retailers and most commercial parts stores and tool distributors.

If you have tight bend, invest in one of the bending tools shown below. You’re going to make mistakes, so it pays to invest in a brake line straightening tool as well. That can save you from reforming an entire section of line.

TIP: Shop on ebay for used S.U.R.&R. bending, flaring and straightening tools. If you can’t find them used, buy them new. Then do your brake job and sell the tools on ebay to recoup most of your investment.

• Reusing brake line fittings—Most of the time, the brake line fittings are rusted to the brake line. If you can get the fitting off, chances are you’ll have to drill out the old steel brake line. Even if you get the old line out, the fitting is already compromised. It’s lost its rust preventative zinc coating. So it will rust much faster if you reinstall it. New fittings are a few bucks. Be a sport and buy new fittings.

• Reusing old flexible brake lines—If the steel brake lines are rusted, chances are the metal ends on your flexible brake lines are rusted as well. They’re cheap (especially at Rockauto.com). Buy new lines and start fresh.

• Not checking to see what type of fittings you have on your vehicle—There are three types of flare connections on vehicles; the SAE double/inverted flare, SAE “bubble” flare and DIN Single Mushroom flare. You can’t make a bubble or mushroom flare using an SAE double flaring kit. Also, DIN bubble/mushroom flare kits are harder to find and are more expensive.

types of brake line flares

Tools you’ll need to repair rusted brake lines

Double flare tool kits

double flare tool kits

Brake Line Tubing Cutters

brake line tubing cutters
Brake line Bending and Straightening Pliers

You’ll have to make some really tight bends with the flare fitting already on the line. Cheap tools can’t do that.


Instead buy a brake line bending pliers. They provide nice tight bends.

brake line pliers
Flare Nut Wrenches and Flare Nut Crowsfeet wrenches

flare nut wrenches and crowsfeet

Posted on by Rick Muscoplat

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