Rick's Free Auto Repair Advice

Brake line splice

Brake line splice instructions

You’ve got two options to replace rusted brake lines

If you have a rusted brake line you’ve got just two options. Option #1: Try to order a pre-bent replacement brake line from the dealer or order a set of pre-bent brake lines online or, Option #2: Buy a coil of brake line and perform a brake line splice. There are advantages and disadvantages to each approach.

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

The pre-bent brake lines sold in kits are often made from stainless steel set of stainless steel pre bent brake linesso 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

They’re 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.

Make your own replacement brake lines or have the shop make them

Performing a brake line splice isn’t hard if you have the right tools and take the time to practice making double or inverted flared ends. Contrary to popular belief it is NOT illegal to make a new section of brake line and splice it into a non-rusted section of your old brake, as long as you use automotive grade SAE double/inverted flare, SAE “bubble” flare and DIN Single Mushroom flare unions and fittings.

See this post to learn about brake line flaring tools.

But you can’t 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 aren’t designed for high brake line pressure and can leak during heavy braking. Single flare plumbing unions are a big NO as well. Single flares can handle the 40-80-psi. in your home’s plumbing system, but a single flare can crack and leak at braking pressures up to 2,000-psi.

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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