Rick's Free Auto Repair Advice

Replace a rusted brake line

How to replace a rusted brake line— YOURSELF

Brake lines rust out quickly if you live in the salt belt. Having a shop replace your rusty brake lines can easily cost upwards of $1,000 or more because it’s a labor-intensive job. In some cases, the shop can buy pre-bent stainless steel brake line kits, but they’re not as easy to install as it sounds. That’s because those kits replicate the path the factory took when running the lines, and sometimes requires removing components.

For example, the carmaker may have run the rear brake line over the top of the fuel tank. The pre-bent replacement kit will duplicate that route, which means the shop will have to drain and remove the fuel tank. But keep in mind, the carmaker did that to save assembly time. As long as the new brake line is run in a safe location, it really doesn’t have to follow the exact same path. That’s one reason why pre-bent kits may not be the way to go.

rusted brake line

Rusted leaking brake line

If you have mechanical knowledge and some tools, a floor jack, and jack stands and are willing to buy or rent the proper brake flaring and bending tools, you can do the entire job yourself for around $250. I’ll show you the step-by-step way to replace rusty brake lines.

Here’s what you’ll need to replace rusted brake lines yourself:

brake line repair tools

Flare nut wrenches • Air chisel with a hammer bit attachment • Rust penetrant—PB Blaster or Liquid Wrench (NOT WD-40 which isn’t a rust penetrant; it’s just a general-purpose lubricant) • A mini-sized tubing cutter • A tubing bending pliers • A really good flaring tool. This is one place you shouldn’t skimp. A cheap flare tool can turn the job into a nightmare.

 

Here are the brake line supplies you’ll need

rusted brake line supplies

I recommend S.U.R. & R. copper-nickel brake line over the other brands. It’s easier to bend. Buy 25’ or 50’ depending on how many lines you want to replace

Buy the best flaring tool out there

The S.U.R. & R. hydraulic flaring tool is the best in the business. It’s idiot-proof and worth every penny. It can even make the difference between a flare that works or one that leaks and causes you to replace a section you just bent and replaced. The kit costs about $235 online. When you’re done with the job, just post the kit on eBay and sell it for about $190 to recoup the majority of your investment

Forget about cheap brake line tubing benders

brake line bending tools

They’re garbage and they only bend a large radius bend. They’re worthless for making the tight bends you’ll need near brake hoses. Use bending pliers.

Here are the two brands I recommend.

brake line bending pliers

Step 1 to replace rusted brake lines: Disconnect the brake line at the ABS modulator or the master cylinder

If you start the job by disconnecting the line at the leak site or the caliper/wheel cylinder, the line will continue to drip and drain the master cylinder. That’ll require a bench bleed when you’re done, which is a complete waste of time. If you disconnect the line under the hood and plug it, you won’t have to perform a master cylinder bench bleed.

Step 2: Disconnect the brake line where it attaches to the brake hose

I’ll show you how to replace a rusted brake line that connects to the rubber brake hose. Those fittings are usually completely rusted to the brass fitting on the brake hose. If your leak is in a horizontal line, skip to the next step.

disconnect leaking brake line

Soak the brake line fitting with rust penetrant. Use a flare nut wrench to see if it will unscrew. If it doesn’t, STOP. These fittings are usually rusted to the brass brake hose connection AND to the steel brake line that runs through the fitting.

If the brake line fitting won’t budge

Rust is like glue, so it seals the threads and prevents the rust penetrant from wicking into the threads to dissolve rust, lubricate and allow the fitting to move. Vibration breaks up the rust and allows the rust penetrant to seep into the threads.

WARNING: The fitting will be rusted. If you don’t follow my instructions, you’ll strip the fitting and possibly damage the brake hose. This requires a bit of patience and finesse to remove

break loose a stuck brake line fitting

I use an air chisel equipped with a hammer bit. Pull the trigger and just let it vibrate the heck out of the fitting. Spray on more rust penetrant and repeat the vibration. Then try again with the flare nut wrench. This works 90% of the time.

However, if your fitting still won’t unscrew from the rubber brake line, you’ll have to but the steel line and splice in a new section, along with a new rubber brake hose.

Use the mini-tubing cutter or long-handled side cutters and cut the tubing. Then try using a deep socket to remove the fitting. If that twists the brass fitting on the brake hose, you’ll have to replace the complete brake hose.

Step 3: Cut out the rusted brake line section

Follow the rusted brake line back until you reach a good section. Use the mini tubing cutter to cut the line. This is where you’ll splice in a new line.

cut the brake line

Step 4: Clean and flare the freshly cut line

Clean off any dirt and debris from the freshly cut line. Slide on a new flare nut to fit the coupler union. Load the line into the S.U.R. & R. flaring tool and perform a two-step double lap flare.

flare brake line

Load the freshly cut line into the S.U.R.&R. die and holder. Slide the line until it’s flush with the end of the die. Then clamp it in place.

flare tool

Load the rounding over punch into the tool

brake line flare

Insert the flare tool into the die and squeeze the trigger. This will round over the brake line and complete the first step in a double lap flare.

Insert the flare punch into the tool and squeeze the trigger. That will complete the flare.

Step 5: Bend the replacement line

bend brake line

Slide a new fitting onto the brake line before you start bending. Then use a bending pliers to form the first bend.

bend brake line

Use the old brake line as a template. Use your bending pliers to duplicate the bends.

Step 6: Connect the new brake line section to the coupler union

Joint the old and new brake line sections with a coupler union. Hold the union with an open end wrench and tighten each fitting with a flare nut wrench

Step 7: Reconnect the brake line at the ABS modulator or master cylinder

Refill the master cylinder. Then bleed the brake line with a handheld vacuum pump.
©, 2020 Rick Muscoplat, Alex Steil

Posted on by Rick Muscoplat

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