How to Flare Brake Lines: A Step-by-Step Guide

To flare brake lines, use a flaring tool to create a precise, angled flare on the end of the brake line. Flaring brake lines ensures a secure and leak-free connection between the lines and fittings.

Flaring brake lines is an essential skill for anyone working on automotive brake systems. It involves using a specialized flaring tool to shape the end of the brake line into a flare that matches the fittings used in the braking system.

This process is crucial for maintaining the integrity and safety of the brake system, as it creates a tight seal that prevents fluid leaks and ensures proper brake function. Understanding how to flare brake lines is a fundamental aspect of automotive maintenance and repair, allowing for the safe and reliable operation of a vehicle’s braking system.

What is Brake Line Flaring?

Brake line flaring is a process in which the end of a brake line is shaped to create a conical or bulbous end that fits tightly against a brake fitting or junction. The flare helps create a strong seal that can withstand the high pressure of brake fluid in the system. Without this secure seal, the brake fluid could leak, leading to decreased brake performance or even failure.

Flaring is done using a specialized tool kit designed to compress and shape the metal tubing in a precise manner. There are different types of flares depending on the vehicle and the type of brake lines used.

Why is Brake Line Flaring Important?

The brake system in a vehicle operates under extremely high hydraulic pressure. A leak or weak spot in the brake line can lead to reduced brake efficiency or total brake failure, which can be dangerous. Flaring ensures that the connection between the brake lines and the fittings is completely sealed, providing the durability and strength needed for safe operation.

For many DIY mechanics, learning how to properly flare brake lines can save money and time, eliminating the need to buy pre-flared lines or have them installed by a professional.

Types of Brake Line Flares

There are two main types of flares used in brake lines:

1. Single Flare

A single flare involves the end of the brake line being spread out in a conical shape. This is the simplest type of flare, but it is not commonly used in modern brake systems because it’s not as strong as other types. Single flares are often found in older cars or non-brake hydraulic systems.

2. Double Flare (Inverted Flare)

The double flare is more common in automotive applications and is widely regarded as the safest and most reliable option for brake lines. The double flare is created by folding the edge of the line back on itself and then shaping it into a flare. This results in a double-thickness flare that can better withstand the high pressure of brake fluid.

3. Bubble Flare

A bubble flare, or ISO flare, is used primarily in European cars. It’s similar to a double flare but is formed differently and results in a “bubble” at the end of the brake line. These are less common in American vehicles, but they are widely used in ABS-equipped cars.

How to Flare Brake Lines

To properly flare brake lines, you’ll need specific tools to achieve a precise and safe flare. Here’s what you’ll need:

• Flaring Tool Kit: A brake line flaring tool is designed to hold the tubing securely while you create the flare. The kit should include dies or adapters for different flare types and sizes.
• Tube Cutter: Used to cut the brake line cleanly and squarely.
• Deburring Tool: After cutting, the inside of the brake line will have sharp edges that need to be smoothed out with a deburring tool.
• Brake Line: Copper-nickel or steel brake lines, depending on your vehicle’s specifications.
• Brake Line Fittings: Ensure you have the correct fittings for the flare type and line size.
• Brake Fluid: If you’re replacing a section of the brake line, you’ll need fresh brake fluid to refill the system.

Step-by-Step Guide to Flaring Brake Lines

Flaring brake lines requires precision and patience. Below is a step-by-step process to guide you through creating a secure flare.

Step 1: Cut the Brake Line

• Measure and cut the brake line to the correct length using a tube cutter.
• Ensure that the cut is clean and square to prevent leaks. An uneven cut can compromise the integrity of the flare.

Step 2: Deburr the Inside of the Brake Line

• Use a deburring tool to clean the inside and outside of the cut brake line. This step removes any sharp edges that could interfere with the flaring process.
• A clean, deburred line ensures the flare will seat properly against the fitting and not cause damage to the flare tool or brake line.

Step 3: Place the Fitting on the Brake Line

• Before flaring, slide the appropriate fitting onto the brake line. Ensure the fitting is facing the correct direction (threads pointing outward). If you forget this step, you’ll need to cut the line and start over.

Step 4: Clamp the Brake Line in the Flaring Tool

• Select the correct die size for your brake line from your flaring kit. The die should match the outer diameter of the brake line (e.g., 3/16” or 1/4”).
• Clamp the brake line into the flaring tool, ensuring it sticks out slightly from the die. The amount of exposed line should equal the thickness of the brake line wall.

Step 5: Create the Flare

• For a double flare, start by using the adapter (the round piece that goes into the end of the tube) to press the brake line down into the die. This folds the line inward, creating the first step of the double flare.
• Remove the adapter and use the cone-shaped tool to press the folded line into a proper inverted flare. Tighten the tool slowly and evenly to ensure the flare is uniform and smooth.
• For a bubble flare, the process is similar, but the adapter will create a bubble-like shape rather than folding the line. Always refer to the manufacturer’s instructions for the correct procedure.

Step 6: Inspect the Flare

• Once you’ve created the flare, inspect it closely. It should be symmetrical, smooth, and free of cracks or deformities. The flare should also seat correctly into the brake fitting.

Step 7: Install the Brake Line

• Once your flare is complete and inspected, install the brake line by screwing the fitting into the appropriate port. Ensure the flare seats firmly against the fitting.
• Tighten the fitting using a wrench, making sure not to overtighten, as this could damage the flare.

Step 8: Test the System

• After installing the brake line, bleed the brake system to remove any trapped air. Refill the brake fluid and test the brake pedal to ensure proper pressure.
• Inspect the flare for leaks by checking for any signs of brake fluid at the fitting. If leaks are present, you may need to refit or reflare the brake line.

Common Mistakes to Avoid

When flaring brake lines, common mistakes to avoid include:

• Forgetting the Fitting: Always remember to slide the brake line fitting onto the tube before creating the flare.
• Uneven Cut: An uneven cut can compromise the flare. Ensure you use a quality tube cutter and take your time when cutting.
• Skipping Deburring: Failing to remove burrs can result in a weak, imperfect flare.
• Using the Wrong Flare Type: Always check your vehicle’s specifications for the correct type of flare (single, double, or bubble).

Frequently Asked Questions

Here are some FAQs about flaring brake lines –

1. Can I flare a brake line without a special tool?

No, you need a specialized flaring tool to create proper flares for brake lines. These tools are designed to create precise, high-pressure flares, which are essential for safety in a brake system.

2. What’s the difference between a single flare and a double flare?

A single flare is a simple, conical shape, while a double flare folds the brake line back on itself before shaping it. Double flares are stronger and more durable, making them the preferred option for most brake systems.

3. Can I reuse old brake line fittings?

Yes, as long as the fittings are in good condition, they can be reused. However, if there is any visible wear or damage, it’s best to replace them to avoid leaks or failure.

4. How long does it take to flare a brake line?

With the right tools and some practice, flaring a brake line can take anywhere from 5 to 15 minutes per flare. The time includes cutting, deburring, flaring, and inspecting the line.

5. Is it okay to use copper brake lines?

Copper brake lines are not recommended because they are soft and prone to cracking under high pressure. Copper-nickel alloy brake lines, on the other hand, are widely used due to their corrosion resistance and durability.

Conclusion

Flaring brake lines is a crucial skill for maintaining or repairing your vehicle’s brake system. By using the proper tools and techniques, you can create secure, leak-proof connections that will ensure safe braking performance. Whether you’re working on an older vehicle or making modifications to a newer model, mastering the art of flaring brake lines can save you both time and money. Always remember to double-check your work for any signs of leaks or weak flares before hitting the road.