Mastering the Double Flare: A Step-by-Step Guide to Perfect Brake Lines
Replacing or repairing brake lines is a crucial skill for any DIY mechanic. While pre-flared lines are available, custom-fabricated lines offer greater flexibility and a perfect fit. Creating a double flare is the preferred method for brake lines, as it creates a robust, leak-proof seal capable of withstanding high pressure. This comprehensive guide will walk you through the entire process, ensuring you can create professional-quality double flares with confidence.
## Why Double Flare? Understanding the Importance
Before diving into the steps, it’s important to understand why a double flare is superior to a single flare in brake line applications.
* **Strength and Durability:** A double flare essentially folds the tubing back on itself, doubling the thickness of the flare where it contacts the fitting. This creates a much stronger and more durable connection, reducing the risk of cracking or splitting under pressure.
* **Leak Resistance:** The double layer of tubing provides a better seal against the fitting. The increased surface area and thickness minimize the chance of leaks, which are unacceptable in a brake system.
* **Industry Standard:** Double flares are the standard for brake lines in most automotive applications. Using any other type of flare could compromise the safety and reliability of your braking system and could fail an inspection.
## Tools and Materials You’ll Need
Gathering the right tools is essential for creating clean, accurate double flares. Here’s a list of what you’ll need:
* **Brake Line Tubing:** Choose the correct size and type of brake line tubing for your vehicle. Common sizes are 3/16 inch and 1/4 inch. Copper-nickel alloy (Cunifer) tubing is highly recommended due to its corrosion resistance, ease of bending, and excellent flaring properties. Steel lines are also available but are more prone to rust.
* **Double Flaring Tool Kit:** This kit is the heart of the operation. A quality kit will include:
* **Flaring Tool:** The main tool for creating the flare. Look for a tool with a solid yoke and hardened steel components.
* **Flaring Dies (Adapters):** These dies are sized to match the brake line tubing diameter and are used to form the initial bubble flare.
* **Tube Cutter:** A specialized tool for cleanly cutting brake line tubing without deforming it.
* **Deburring Tool:** Used to remove any burrs from the inside and outside of the cut tubing. This is crucial for a proper flare.
* **Tube Bender:** This tool helps you create smooth, accurate bends in the brake line without kinking or collapsing the tubing. Avoid bending the tubing by hand, as this often results in kinks.
* **Wrench Set:** For tightening the fittings onto the flared brake lines. Use the correct size wrench to avoid rounding off the fitting.
* **Safety Glasses:** Protect your eyes from metal shavings and debris.
* **Gloves:** Protect your hands and provide a better grip.
* **Measuring Tape or Ruler:** For accurately measuring the length of brake line needed.
* **Bench Vise (Optional but Recommended):** A vise can help hold the flaring tool securely, making the flaring process easier and more accurate.
* **Brake Fluid:** For bleeding the brakes after replacing the lines. Use the correct type of brake fluid specified for your vehicle (DOT 3, DOT 4, or DOT 5.1).
* **Penetrating Oil:** Can be helpful for loosening corroded fittings.
* **Rags or Shop Towels:** For cleaning up spills and wiping down tools.
## Step-by-Step Guide to Making a Double Flare
Now that you have your tools and materials, let’s get started. Follow these steps carefully to create perfect double flares.
**Step 1: Preparation – Safety First!**
* **Safety Glasses On:** Always wear safety glasses to protect your eyes from flying debris.
* **Secure the Vehicle:** If you’re working on brake lines that are still connected to the vehicle, ensure the vehicle is safely supported on jack stands. Never work under a vehicle supported only by a jack.
* **Disconnect the Battery (Recommended):** While not strictly necessary for brake line work itself, disconnecting the negative battery terminal can prevent accidental electrical shorts while you’re working in the engine compartment or under the vehicle.
**Step 2: Measuring and Cutting the Brake Line**
* **Accurate Measurement:** Carefully measure the length of brake line you need. It’s always better to err on the side of being slightly too long, as you can always trim it later. Consider the routing of the line and any bends that need to be made.
* **Clean Cut:** Use the tube cutter to cut the brake line to the desired length. Rotate the cutter around the tubing, tightening it slightly with each rotation. Avoid over-tightening, as this can deform the tubing. The goal is a clean, square cut.
**Step 3: Deburring the Cut End**
* **Inner and Outer Burrs:** After cutting, there will be burrs on the inside and outside of the tubing. These burrs must be removed to ensure a proper flare.
* **Deburring Tool:** Use the deburring tool to carefully remove the burrs. Rotate the tool inside the tubing to remove the inner burrs and then use the outer deburring edge to remove the outer burrs. Make sure the end of the tubing is smooth and free of any sharp edges.
**Step 4: Preparing the Flaring Tool**
* **Select the Correct Die:** Choose the flaring die (adapter) that corresponds to the diameter of your brake line tubing. The die should fit snugly into the end of the tubing.
* **Insert the Tubing:** Place the brake line tubing into the flaring tool. The amount of tubing that protrudes from the tool is critical. Consult your flaring tool’s instructions for the correct amount. Generally, it’s a very small amount – just enough for the die to properly form the initial bubble flare. If the instructions are missing, experiment on a scrap piece of tubing. Too much tubing will result in an improperly formed flare. Too little tubing will result in a weak flare.
* **Secure the Tool:** Tighten the flaring tool’s clamping mechanism to securely hold the tubing in place. If you have a bench vise, use it to hold the flaring tool steady.
**Step 5: Creating the First Flare (Bubble Flare)**
* **Insert the Die:** Insert the correct size flaring die into the end of the tubing. Ensure it’s seated properly.
* **Tighten the Flaring Tool:** Using the flaring tool’s handle, carefully tighten the tool to press the die into the tubing. Apply steady, even pressure. You should feel the tubing forming the bubble flare. Follow the instructions that came with your tool, typically you will need to tighten until the tool bottoms out. Do not overtighten, as this could damage the tubing or the tool.
* **Remove the Die:** Loosen the flaring tool and remove the die. You should now have a bubble-shaped flare at the end of the tubing.
**Step 6: Creating the Double Flare**
* **Remove the Die (If Applicable):** Some flaring tool kits use the same die for both the initial bubble flare and the final double flare. Others use a different tool entirely. If your kit uses the same die, remove it from the tubing.
* **Position the Flaring Tool:** Ensure the flaring tool is still securely holding the tubing.
* **Final Flare:** Using the flaring tool, press the cone shaped end down into the bubble flare you already created, flattening it back on itself. Follow the instructions that came with your tool, typically you will need to tighten until the tool bottoms out. Apply steady, even pressure. The goal is to create a smooth, even double flare that is symmetrical and free of cracks or imperfections. You will feel the metal compressing as you tighten.
* **Inspect the Flare:** Once you’ve tightened the flaring tool, loosen it and carefully remove the brake line. Inspect the double flare closely. It should be smooth, even, and symmetrical. There should be no cracks, splits, or imperfections. The inside surface of the flare should be clean and smooth. If the flare looks good, proceed to the next step. If not, cut off the flared end and repeat the process from Step 2, paying close attention to the amount of tubing protruding from the flaring tool and the amount of pressure applied.
**Step 7: Connecting the Brake Line**
* **Install Fittings:** Slide the correct fittings (usually a union, or a fitting to connect to the brake caliper or master cylinder) onto the brake line, with the threaded end facing the flare.
* **Connect the Line:** Carefully insert the flared end of the brake line into the receiving fitting on the vehicle. Ensure the flare seats properly against the fitting.
* **Tighten the Fitting:** Using the correct size wrench, tighten the fitting to the manufacturer’s specified torque. Avoid over-tightening, as this can damage the fitting or the flare. A flare nut wrench is recommended to avoid rounding the corners of the fitting.
* **Repeat on the Other End:** Repeat steps 2-7 on the other end of the brake line, if necessary.
**Step 8: Bending the Brake Line (If Necessary)**
* **Gentle Bends:** Use the tube bender to create smooth, gentle bends in the brake line. Avoid sharp bends, as these can restrict fluid flow and weaken the line.
* **Follow the Original Routing:** When bending the brake line, try to follow the original routing as closely as possible. This will ensure that the line doesn’t rub against any other components or become damaged.
* **Check for Kinks:** After bending the brake line, inspect it carefully for kinks or collapses. If you find any, discard the line and start over.
**Step 9: Securing the Brake Line**
* **Use Clips or Fasteners:** Secure the brake line to the vehicle using the original clips or fasteners. This will prevent the line from vibrating or rubbing against other components.
* **Adequate Clearance:** Ensure that the brake line has adequate clearance from any moving parts, such as suspension components or exhaust pipes.
**Step 10: Bleeding the Brakes**
* **Essential Step:** After replacing any brake lines, it’s essential to bleed the brakes to remove any air that may have entered the system. Air in the brake lines can cause a spongy brake pedal and reduce braking performance.
* **Bleeding Procedure:** Follow the manufacturer’s recommended brake bleeding procedure for your vehicle. This typically involves opening the bleeder screws on each brake caliper or wheel cylinder and allowing brake fluid to flow out until all the air is removed.
* **Check Fluid Level:** Be sure to check the brake fluid level in the master cylinder frequently during the bleeding process and top it off as needed.
## Troubleshooting Common Double Flaring Problems
Even with careful attention to detail, you may encounter some common problems when making double flares. Here’s how to troubleshoot them:
* **Cracked or Split Flare:** This is usually caused by overtightening the flaring tool, using the wrong size die, or using damaged or corroded tubing. Make sure you have a good clean square end on your tubing, the correct die, and are not over tightening the flare.
* **Uneven Flare:** This can be caused by an improperly aligned flaring tool, uneven pressure, or a burr on the tubing. Make sure you have a clean deburred edge on your brake line.
* **Flare Not Sealing Properly:** This can be caused by a damaged or dirty flare, a loose fitting, or a damaged fitting.
* **Kinked or Collapsed Tubing:** This is usually caused by bending the tubing too sharply without a tube bender. Ensure you are using the correct tube bender to achieve a smooth consistent bend.
## Tips for Success
* **Practice Makes Perfect:** Before working on your vehicle’s brake lines, practice making double flares on scrap pieces of tubing. This will help you get a feel for the process and avoid making mistakes on your actual brake lines.
* **Use Quality Tools:** Investing in a quality flaring tool kit and tube bender will make the job much easier and produce better results.
* **Follow Instructions Carefully:** Always follow the instructions that come with your flaring tool kit. These instructions will provide specific guidance on how to use the tool properly and achieve the best results.
* **Take Your Time:** Don’t rush the process. Take your time and pay attention to detail. A properly made double flare is essential for the safety and reliability of your braking system.
* **Inspect Everything:** Inspect each flare carefully before installing the brake line. If you find any imperfections, discard the line and start over.
* **Cleanliness is Key:** Keep your tools and work area clean. Dirt and debris can contaminate the brake fluid and compromise the performance of your braking system.
## Choosing the Right Brake Line Tubing
The type of brake line tubing you choose is crucial for the longevity and performance of your brake system. Here’s a breakdown of the common options:
* **Steel Brake Lines:** Steel lines are the most traditional option and are relatively inexpensive. However, they are prone to rust, especially in areas with harsh winters or salty roads. Rust can weaken the lines and eventually cause them to leak.
* **Copper-Nickel Alloy (Cunifer) Brake Lines:** Cunifer brake lines are a superior alternative to steel. They are highly corrosion resistant, easy to bend and flare, and offer excellent durability. While they are slightly more expensive than steel lines, the added benefits make them a worthwhile investment. Cunifer is highly recommended for its ease of use and longevity.
* **Stainless Steel Brake Lines:** Stainless steel lines offer excellent corrosion resistance and strength. However, they are more difficult to bend and flare than Cunifer or steel lines. They also tend to be more expensive. Flexible stainless steel braided lines are typically used as hoses to connect to the brake calipers but should not be used in place of the hard lines running along the chassis.
## Alternatives to Flaring: Compression Fittings (Use with Caution!)**
While double flaring is the preferred method for brake line connections, compression fittings are sometimes used as a temporary repair or in situations where flaring is difficult. However, it’s important to understand the limitations and potential risks associated with compression fittings on brake lines.
* **Not Recommended for High-Pressure Systems:** Compression fittings are generally not recommended for use in high-pressure brake systems. They are more prone to leaks than properly made double flares.
* **Potential for Failure:** Compression fittings can loosen or fail over time, especially in environments with vibration or temperature fluctuations.
* **May Not Be Legal:** In some jurisdictions, the use of compression fittings on brake lines may be illegal. Check your local regulations before using them.
* **Emergency Use Only:** If you must use a compression fitting, do so only as a temporary repair to get your vehicle to a safe location where you can properly repair the brake line with a double flare. Then replace the line with a proper flare as soon as possible.
## Conclusion
Mastering the double flare technique is an invaluable skill for any automotive enthusiast or DIY mechanic. By following these detailed steps, using the right tools, and paying close attention to detail, you can create professional-quality brake lines that are safe, reliable, and long-lasting. Remember to always prioritize safety and consult your vehicle’s service manual for specific instructions and torque specifications. With practice and patience, you’ll be able to confidently tackle brake line repairs and replacements, ensuring the safety and performance of your vehicle’s braking system. Drive safe!