What is a brake line flare tool used for? A brake line flare tool is used to create a sealed, flared end on a metal brake line tube. This flare allows the line to connect securely to fittings, like those found on brake calipers or master cylinders, ensuring a leak-free hydraulic seal.
Repairing your vehicle’s brake lines can seem like a big job. However, with the right tools and steps, you can successfully create reliable, leak-free connections. This guide will walk you through the entire process of using a brake line flare tool. We will cover the essential brake line flaring techniques needed for safe, lasting repairs, especially when repairing rusted brake lines.
Why Flaring Brake Lines Is Necessary
Brake systems rely on hydraulic pressure to stop your car. If a brake line leaks, pressure drops, and your brakes fail. You must seal the end of the tubing perfectly. A flare creates this tight seal against a mating surface on a brake fitting.
Can I reuse old flares? No. Once a flare is assembled, it should never be reused. You must cut off the old flare and create a brand new one when working on a section of line.
Types of Flares You Will Encounter
Different brake systems use different flare styles. Knowing which one you need is the first critical step. Choosing the right brake line flare size depends entirely on your vehicle’s specifications.
SAE Flares (Standard)
These are common on older American cars and some trucks.
- Single Flare Brake Line Tool: This creates a basic 45-degree flare. It is simple but less strong. It is often used for steel or annealed copper-nickel tubing.
- Double Flare Tool Usage: This is the standard for most modern hydraulic brake lines in the US. It involves creating a 45-degree flare and then folding the metal back upon itself to create a stronger, double-thick seal. This prevents leaks and tube cracking.
Metric Flares
These are common on European and Asian vehicles.
- Bubble Flare Brake Line Tool: This creates a rounded, bubble-like flare, usually 45 degrees. It is simpler than the double flare but very strong. This is the most common metric flare style.
- Metric Brake Line Flaring: When working on metric lines, ensure your tool set includes the necessary metric dies and adapters, as the fitting sizes differ from SAE standards.
| Flare Type | Common Use | Angle | Strength |
|---|---|---|---|
| Single Flare | Older, low-pressure applications | 45 degrees | Moderate |
| Double Flare | Modern hydraulic brakes (SAE) | 45 degrees (folded) | High |
| Bubble Flare | Modern hydraulic brakes (Metric) | 45 degrees (rounded) | High |
Preparing Your Materials and Tools
Before you start shaping the metal, preparation is key to success. Good preparation ensures clean cuts and proper flaring annealed tubing.
Selecting the Right Tubing
Never use regular plumbing pipe or soft copper tubing for brake lines. Brake lines must handle very high pressure.
- Use Approved Material: Only use tubing rated for hydraulic brake systems. Common materials include NiCopp (copper-nickel alloy), standard steel, or stainless steel.
- Annealed Tubing: Tubing must be flaring annealed tubing—meaning it is soft enough to be shaped without cracking. New tubing bought for repairs is usually already annealed.
- Choosing the Right Brake Line Flare Size: Brake lines come in set outer diameters (OD), such as 3/16″, 1/4″, or 5/16″. You must match the tubing OD exactly to the tool adapter and the fitting you are connecting to.
Required Tools Checklist
You need more than just the flare tool itself to successfully how to flare brake lines.
- Brake Line Flaring Tool Kit (matching the flare type you need).
- Tubing Cutter (not a hacksaw, which leaves burrs).
- Deburring Tool (or a sharp utility knife blade).
- Vise or sturdy clamp to hold the tool securely.
- Safety glasses and gloves.
- Brake fluid for cleanup.
Step-by-Step Guide to Flaring Brake Lines
The following steps focus on the double flare tool usage, as it is the most common for modern vehicle repairs requiring high strength. The basic principles apply to single flares and bubble flares too, with minor adjustments to the final step.
Step 1: Measuring and Cutting the Line
Accurate cutting prevents waste and ensures a good fit.
- Measure the Length: Determine how much new line you need. Measure twice and cut once.
- Secure the Cutter: Clamp the tubing cutter around the line.
- Make a Clean Cut: Slowly turn the cutter handle, tightening it slightly with each rotation. Do not overtighten quickly. This ensures a straight, clean cut, vital for a good flare.
Step 2: Deburring and Cleaning
This step is often skipped, leading to flare failure.
- Remove Inner Burrs: Use the dedicated internal reamer (often part of the cutter or flare tool kit) to scrape away the sharp ridge (burr) left inside the tube end after cutting.
- Remove Outer Burrs: Use the deburring tool or a very gentle pass with a file to remove the outside burr on the tube end.
- Wipe Clean: Wipe the outside and inside of the tube end completely clean. Dirt or metal shavings interfere with the flare seal.
Step 3: Installing the Nut and Mounting in the Tool
This step ensures you do not forget the necessary component.
- Slide on the Flare Nut: Before flaring, slide the flare nut onto the tube end. Make sure the flared end will point toward the nut when you are done. If you forget this, you must cut the line and start over.
- Clamp the Tube: Insert the tube into the body of the flaring tool. The tube must stick out by the precise length specified in your tool’s instructions. This distance is crucial for SAE brake line flares and metric flares alike.
- Tighten the Clamp: Tighten the clamping screws evenly until the tube is held firmly and will not move.
Step 4: Creating the Initial 45-Degree Flare (The First Stage)
This step forms the basic cone shape.
- Insert the Flaring Cone: Screw the flaring cone (or punch) into the tool body until it makes contact with the end of the tube.
- Apply Pressure: Turn the yoke handle clockwise. You will feel strong resistance as the cone forces the metal outward against the die block inside the tool.
- Torque: Tighten until the manufacturer specifies the required torque or until the turning resistance significantly increases. Do not force it past a reasonable stopping point, especially with softer metals like NiCopp.
- Release: Unscrew the yoke handle to release the pressure. Remove the flaring cone.
Step 5: Finishing the Double Flare (SAE Specific)
This step is what creates the strong seal required for high-pressure lines.
- Remove the Tube: Loosen the clamp screws and remove the tube. You should see a neat, 45-degree cone shape.
- Flare Bending: Carefully bend the flared end over so it is almost parallel to the tube shaft, but not completely flat. This prepares the metal for the second fold.
- Reinsert for the Second Flare: Place the tube back into the flaring tool. This time, you will use a different adapter (often called the seating or sealing adapter), which pushes directly onto the 45-degree flare itself.
- Second Flattening: Tighten the yoke handle again. This second press forces the 45-degree cone face to seal tightly against itself, creating a double layer—the double flare.
- Final Check: Remove the tube. The end should look like a thick, rounded lip, not a sharp cone.
Note for Bubble Flare Brake Line Tool usage: For a bubble flare, you skip Step 5 entirely. Instead of using a second flat press, you use the bubble adapter to form a smooth, round bubble shape at the end of the tube after the initial 45-degree flare.
Advanced Considerations in Brake Line Flaring
Successful flaring involves more than just turning a wrench. It requires attention to material behavior and precise tool alignment.
Working with Different Materials
The way metal reacts to pressure differs greatly between materials.
- Steel Lines: Steel is hard. It requires more force to form the flare. It is prone to cracking if over-worked, so you must use the correct torque settings.
- NiCopp (Copper-Nickel): This material is much softer and easier to work with. It requires less force. Be careful not to deform the tube wall when clamping, as this can cause weak spots. Flaring annealed tubing like NiCopp is often easier for beginners.
- Stainless Steel: This is the hardest material. It demands specialized, heavy-duty flaring tools designed specifically for stainless steel, as standard kits may break or fail to achieve the proper flare.
Maintaining the Tool
Your flare tool relies on precise geometry. Keep it clean.
- Die Condition: Inspect the die block regularly. Any nicks or scratches on the inner surface where the tube rests will transfer to your flare, causing leaks.
- Thread Lubrication: Apply a light coat of anti-seize compound to the threads of the yoke handle and the flaring cone to ensure smooth operation and consistent pressure application.
Inspecting and Testing Your New Flare
A flare that looks good might still leak under pressure. Proper inspection prevents dangerous failures down the road.
Visual Inspection
After removing the tube from the tool:
- Check for Cracks: Look closely at the flared edge using magnification if possible. Any hairline cracks mean the flare is bad and must be cut off and redone.
- Symmetry: The flare should be evenly formed all the way around the tube. Uneven flares indicate the tube was not seated perfectly straight in the tool.
- Double Flare Sealing: For double flares, the thickness at the very end should look consistent—like a solid, slightly rounded edge.
Installation and Leak Testing
When you install the new flared line:
- Seating the Flare: Screw the flare nut into the mating component (e.g., caliper). Tighten it firmly by hand first.
- Torque Specification: Use a backup wrench on the component body and use a flare nut wrench to tighten the nut to the manufacturer’s specific torque setting. Over-tightening can crush the flare, causing a leak. Under-tightening will definitely leak.
- Bleeding the System: Once installed, you must bleed the entire brake system to remove air.
- Pressure Test: After bleeding, apply firm, steady pressure to the brake pedal (using a helper or a specialized pressure bleeding tool). Hold the pressure for several minutes while inspecting every new flare connection for signs of moisture or weeping. If any dampness appears, immediately release pressure, remove the line, cut the flare off, and start over.
Troubleshooting Common Flaring Mistakes
Even with careful practice, mistakes happen. Here are ways to fix issues related to brake line flaring techniques.
| Problem | Likely Cause | Solution |
|---|---|---|
| Flare is uneven or lopsided. | Tube was not seated perfectly straight in the tool block, or clamping pressure was uneven. | Re-cut the line completely. Ensure the tube is perfectly perpendicular to the die block during clamping. |
| Flare cracks during the process. | Metal is too cold (steel), or the tool was tightened too fast/hard (overworking the metal). | If using steel, try warming the area slightly (carefully). Slow down the turning of the yoke handle. |
| The flare leaks after installation. | Incomplete double flare (SAE) or insufficient final torque on the flare nut. | Cut the line back past the damaged area. Re-flare the line, ensuring you complete both stages of the double flare, and torque the nut correctly. |
| Tube slips in the tool during flaring. | Clamping screws were not tight enough, or the tube OD is slightly undersized. | Tighten the clamp screws more firmly. If the problem persists, the tubing may be incorrect for the tool size. |
Summary of Best Practices for Flaring
To ensure professional results every time you how to flare brake lines:
- Always use a dedicated tubing cutter for clean, straight ends.
- Deburr both the inside and outside of the cut tube end thoroughly.
- Never forget to slide the flare nut onto the tube before you start flaring.
- Follow the specific torque requirements for the tool setup. Consistency builds reliability.
- When in doubt, always cut the line back and try again. Brake safety is non-negotiable.
Frequently Asked Questions (FAQ)
Can I make a bubble flare using a single flare tool?
Generally, no. While a single flare brake line tool creates a basic cone, it lacks the specific rounded die shape needed to create a true bubble flare. You need a dedicated bubble flare brake line tool or a comprehensive kit that includes the correct adapter dies for bubble flares, which are distinct from SAE dies.
What is the difference between SAE and metric brake line flares?
The main difference lies in the fitting thread pitch and the flare style. SAE systems typically use 45-degree flares (often double flares), while metric systems often use 45-degree bubble flares. The physical thread diameters and spacing on the nuts are different, meaning an SAE fitting will not seal properly on a metric line, even if the flare angle is close.
How much tubing should stick out of the flaring tool?
This measurement is critical and depends on the specific tool and flare type. For a double flare tool usage, the measurement ensures enough material is available for both the initial flare and the final folding action. Always consult the instruction manual that came with your specific flaring kit for the precise protrusion distance required before clamping the tube.
Is it safe to use old brake line tubing after cutting off a bad section?
Yes, provided the remaining tubing is not significantly corroded or kinked. If you cut out a rusted section, the remaining line must be inspected carefully. If it is still structurally sound and you are flaring annealed tubing or new material to connect to it, the repair is safe. However, if the old tubing shows pitting or thinning, replace the entire section from a connection point to the next.