Air on Brake Lines: Symptoms & DIY Bleeding

Hydraulic brake systems, a critical component regulated by entities like the National Highway Traffic Safety Administration (NHTSA), rely on the incompressibility of brake fluid to effectively transmit force. The presence of air on brake lines, often introduced during maintenance involving components like brake calipers, compromises this system’s integrity, leading to a spongy pedal feel. DIY bleeding, a procedure often executed using tools from manufacturers like Motive Products, aims to eliminate these air pockets and restore optimal braking performance, preventing potential hazards.

Diagnosing and Addressing Air in Your Brake Lines

When air infiltrates your brake lines, it compromises the hydraulic system’s ability to transmit force effectively. This leads to a noticeable reduction in braking performance, potentially creating a dangerous situation. Understanding the symptoms of air in brake lines and knowing how to safely bleed them are crucial for vehicle maintenance and safety. This guide will walk you through both aspects.

Recognizing the Symptoms of Air in Brake Lines

The presence of air in your brake lines manifests in several ways. These symptoms range from subtle changes in pedal feel to significant reductions in stopping power. Recognizing these indicators early can help you address the problem before it escalates.

• Spongy or Soft Brake Pedal: This is the most common symptom. Instead of feeling firm and responsive when you press the brake pedal, it will feel soft, mushy, and require excessive travel before the brakes engage. This is due to the compressibility of air, unlike the incompressible nature of brake fluid.

• Reduced Braking Power: Even with significant pedal pressure, your vehicle may take longer to stop, or you may notice a decrease in overall braking effectiveness. This can be particularly noticeable in emergency braking situations.

• Inconsistent Brake Pedal Feel: The brake pedal may feel different each time you press it. Sometimes it might feel firmer than others, but generally, it will still exhibit a spongy quality. This inconsistency arises from the varying amount of air being compressed within the system.

• Brake Pedal Goes to the Floor: In severe cases, the brake pedal may travel all the way to the floor with minimal resistance, indicating a substantial amount of air in the system. This is a critical safety issue that requires immediate attention.

• ABS Light Illumination: While the ABS light can indicate various issues with the Anti-lock Braking System, it can also be triggered by air in the brake lines affecting the system’s sensors and operation. It is always important to scan your vehicle for error codes to diagnose the source of ABS light.

• Unusual Noises: You might hear gurgling or hissing sounds when you apply the brakes. These sounds are caused by the movement of air within the brake lines and master cylinder.

DIY Brake Bleeding: A Step-by-Step Guide

Bleeding your brakes involves removing trapped air from the brake lines and replacing it with fresh brake fluid. Always consult your vehicle’s repair manual for specific instructions and torque specifications related to your vehicle’s braking system. This is a general guide and it is crucial to prioritize safety:

1. Gather Your Supplies:

   • New brake fluid (DOT 3 or DOT 4, consult your owner’s manual).
   • A clear plastic hose.
   • A wrench that fits your brake bleeder screws.
   • A container to collect old brake fluid.
   • Safety glasses and gloves.
   • Jack and jack stands.
   • A helper (optional, but highly recommended).

2. Prepare the Vehicle:

   • Park your vehicle on a level surface.
   • Loosen the lug nuts on the wheels you will be working on.
   • Jack up the vehicle and securely support it with jack stands.
   • Remove the wheels.

3. Locate the Bleeder Screws:

   • The bleeder screws are typically found on the brake calipers or wheel cylinders. They are small, screw-like valves.

4. Prepare the Bleeding Setup:

   • Attach one end of the clear plastic hose to the bleeder screw.
   • Place the other end of the hose into the container for collecting old brake fluid. Make sure the end of the hose is submerged in the fluid to prevent air from being drawn back into the system.

5. Bleeding the Brakes (Two-Person Method):

   • Helper: Have your helper slowly press the brake pedal down and hold it.
   • You: Open the bleeder screw (usually a quarter to half turn) using the wrench. You will see brake fluid and possibly air bubbles flowing through the hose.
   • You: Once the fluid flow stops or slows to a drip, close the bleeder screw tightly.
   • Helper: Slowly release the brake pedal.
   • Repeat these steps until you see a steady stream of brake fluid without any air bubbles. Ensure the brake fluid reservoir never runs dry during this process. If air is drawn in from an empty reservoir, you’ll have to start the bleeding process again from the wheel furthest from the master cylinder.

6. Bleeding the Brakes (One-Person Method – Using a Bleeder Kit):

   • If you are using a one-person brake bleeder kit (such as a vacuum bleeder or pressure bleeder), follow the instructions provided with the kit. These kits typically create a vacuum or pressure that assists in drawing the brake fluid through the system.
   • The principle remains the same: you are removing old fluid and air, ensuring the reservoir never runs dry.

7. Repeat for All Wheels:

   • Bleed each brake starting with the wheel furthest from the master cylinder and ending with the wheel closest to the master cylinder. The typical order is:
     1. Right Rear
     2. Left Rear
     3. Right Front
     4. Left Front

8. Check and Top Off Brake Fluid:

   • After bleeding all the brakes, check the brake fluid level in the master cylinder reservoir. Top it off to the "MAX" line with fresh brake fluid.

9. Test the Brakes:

   • Pump the brake pedal several times to ensure it feels firm and responsive.
   • Carefully test the brakes by driving the vehicle slowly in a safe area. Ensure the brakes engage properly and the vehicle stops smoothly.

Important Considerations

• Brake Fluid Compatibility: Always use the brake fluid type specified in your vehicle’s owner’s manual. Mixing different types of brake fluid can damage the braking system.
• Contamination: Brake fluid is hygroscopic, meaning it absorbs moisture from the air. Always use fresh brake fluid from a sealed container. Discard any unused brake fluid that has been opened for an extended period.
• Bleeder Screw Condition: If the bleeder screws are rusted or damaged, they may be difficult to open or close properly. Consider replacing them if necessary.
• Professional Assistance: If you are not comfortable performing this procedure yourself, or if you encounter any difficulties, consult a qualified mechanic. Brakes are a critical safety component, and it’s essential to ensure they are functioning correctly.

Troubleshooting Persistent Air

If you bleed the brakes multiple times and still experience a spongy pedal, there may be an underlying issue:

So, there you have it! Recognizing the symptoms of air on brake lines and knowing how to bleed them yourself can save you money and keep you safe on the road. If you’re not comfortable tackling this yourself, don’t hesitate to take your car to a trusted mechanic. Better safe than sorry when it comes to brakes!