The Complete Guide to Bleeding Your Car’s Brakes
Bleeding the brakes is an essential maintenance task that every car owner should know how to do. Over time, air can get trapped in your vehicle’s brake lines, leading to a spongy or soft brake pedal feel. This reduces braking performance and can be a serious safety issue. Bleeding the brakes removes this trapped air, restoring proper brake function.
In this comprehensive guide, we’ll cover everything you need to know about bleeding brakes – what it is, why it’s important, the tools and supplies needed, and step-by-step instructions for getting the job done right. Whether you’re a seasoned DIYer or a beginner looking to learn, this article will give you the knowledge and confidence to bleed your own brakes. Let’s dive in!
What is Brake Bleeding?
Brake bleeding is the process of removing air bubbles that have become trapped in the hydraulic brake system. Your car’s brakes rely on brake fluid to transfer the force from your foot pressing the pedal to the brake pads and calipers that stop the wheels. Brake fluid cannot be compressed, allowing this pressure transfer.
However, air can be compressed. When air bubbles enter the brake lines, they reduce the hydraulic pressure and cause a soft or spongy brake pedal. The brakes may still work, but more pedal travel is required and braking performance is diminished. In extreme cases, trapped air can cause a complete loss of braking ability – a dangerous situation.
Bleeding the brakes involves opening bleeder valves located on the brake calipers or wheel cylinders to allow the trapped air to escape. Fresh brake fluid is added to the master cylinder reservoir to replace the fluid and air removed during bleeding. When done properly, brake bleeding restores the brake system to optimal performance.
Why is Brake Bleeding Necessary?
There are several reasons why air can enter the brake hydraulic system and make bleeding necessary:
- Routine maintenance: Brake fluid absorbs moisture over time, lowering its boiling point and promoting internal corrosion. Many manufacturers recommend replacing brake fluid every 1-2 years. Bleeding is done as part of this fluid flush.
- Replacing brake components: If you replace calipers, wheel cylinders, brake hoses, or other hydraulic parts, some air will enter the system. The brakes need to be bled to remove this air.
- Low brake fluid: If the master cylinder runs low on fluid, from a leak or neglect, air can be drawn into the brake lines. Topping up the fluid is not enough – the system has to be bled.
- Overheating: In extreme conditions like mountain driving or racing, the brake fluid can overheat and boil from the intense heat. This forms air bubbles in the fluid that have to be removed by bleeding.
Soft or fading brake pedal feel is the most common symptom that the brakes need bleeding. If your car requires more pedal effort than usual to stop, or the pedal travels further before the brakes engage, there is likely air in the system. Bleeding the brakes will firm up the pedal and restore lost braking performance.
Tools and Supplies Needed
Brake bleeding is a straightforward process that requires only a few basic tools:
- Brake fluid: Use the type specified for your vehicle, such as DOT 3, DOT 4, or DOT 5.1. Never mix different types. Refer to your owner’s manual or the master cylinder reservoir cap.
- Clear plastic tubing: You’ll need about 2-3 feet of 1/4″ or 3/16″ ID clear tubing to fit over the bleeder valves. The clear tubing allows you to see air bubbles during bleeding.
- Wrench for bleeder valves: A box-end wrench or line wrench in the correct size for the bleeder screws. Usually 8mm or 10mm.
- Brake fluid catch container: Disposable plastic bottle, oil catch can, etc. to catch the waste fluid.
- Turkey baster or syringe: For adding fluid to the reservoir and pumping fluid through the bleeder valves.
- Protective gloves and eyewear: Brake fluid is corrosive and will damage paint. Wear gloves and safety glasses.
- Assistant: Bleeding brakes is a two-person job – one to pump the pedal and one to open/close the bleeder valves.
- Floor jack and jack stands: If you need to raise the vehicle to access the bleeder valves. Chocks for the wheels.
- Rags or shop towels: For cleanup of spills and drips.
Having these tools and supplies on hand before starting will make the brake bleeding process much smoother. It’s also a good idea to have your vehicle’s service manual handy for reference on bleeding order and any special procedures.
Step-by-Step Brake Bleeding Instructions
With the necessary tools gathered and a helper recruited, it’s time to get started. The general process for bleeding brakes is as follows:
Step 1: Prepare the Vehicle
- Park on a level surface and set the parking brake.
- Chock the wheels to keep the vehicle from rolling.
- If you need to raise the vehicle to access the bleeder screws, do so now with a floor jack and secure it on jack stands. Never work under a vehicle supported only by a jack.
Step 2: Check the Brake Fluid Level
- Pop the hood and locate the brake master cylinder reservoir. It is usually mounted on the firewall or fender on the driver’s side.
- Check the fluid level – if it is low, top it up to the “MAX” line with fresh brake fluid. Do not allow the reservoir to run empty during bleeding or air will be introduced into the system.
Step 3: Locate the Bleeder Screws
- Each brake caliper or wheel cylinder will have a bleeder screw, usually located at the top. The bleeder screw has a small nipple that the plastic tubing will fit over. If the bleeder screw is seized or stripped, you may need to replace the whole caliper or wheel cylinder.
Step 4: Connect the Catch Container and Tubing
- Place the catch container on the ground under the bleeder screw.
- Slip one end of the plastic tubing over the bleeder screw nipple and put the other end into the catch container. Make sure the tubing is long enough to reach the container without kinking.
Step 5: Pump the Brake Pedal
- Have your assistant sit in the driver’s seat and pump the brake pedal slowly 3-4 times. This builds up hydraulic pressure in the system.
- Tell them to hold the pedal down firmly on the last pump and keep it there until you tell them to release it.
Step 6: Open the Bleeder Screw
- While your assistant holds pressure on the pedal, use the wrench to open the bleeder screw about 1/4 turn. Fluid and air bubbles will flow out of the bleeder, through the tubing, and into the catch container. The pedal will sink to the floor as the fluid escapes.
- Keep the screw open until the fluid stream no longer has bubbles.
Step 7: Close the Bleeder Screw
- When the fluid is running clear and bubble-free, tell your assistant to slowly release the brake pedal.
- As soon as the pedal starts coming up, tighten the bleeder screw. This prevents air from being sucked back into the system. The pedal should be held down until the bleeder is closed.
Step 8: Repeat Steps 5-7
- Continue this process of pumping the pedal, opening the bleeder, closing the bleeder, and releasing the pedal until no more air comes out. It may take 5-10 cycles to fully purge all the air. Check the master cylinder fluid level frequently and top up as needed. If the fluid runs empty, you’ll have to start the bleeding process over.
Step 9: Move to the Next Wheel
- Once you have clean, bubble-free fluid flowing from one bleeder, close it tightly and move to the next wheel. The sequence is important to follow – start with the wheel furthest from the master cylinder and work your way closer. A typical sequence is passenger rear, driver rear, passenger front, driver front. Your vehicle’s service manual will specify the correct order.
Step 10: Test the Pedal and Check for Leaks
- After bleeding all four brakes, have your assistant apply the brake pedal several times with the engine off. The pedal should be high and firm, not spongy or soft.
- Start the engine and test the pedal again – there should be much less travel required to engage the brakes. Check all the bleeder screws for signs of fluid leaks. A leak will allow air to be drawn in, undoing your efforts.
Step 11: Bed in the Brakes
- If you replaced the brake fluid as part of a complete system flush, it’s a good idea to bed in the brakes before driving normally. This helps the new fluid reach optimal performance.
- Find an open stretch of road and accelerate to about 60 mph. Brake firmly down to about 20 mph without coming to a complete stop. Repeat this process 2-3 times to heat up the fluid and pads. Allow the brakes to cool before parking the vehicle.
Brake Bleeding Tips and Tricks
Here are a few additional tips to make your brake bleeding job easier and more effective:
- Protect your paint: Brake fluid will eat through paint in seconds. Immediately wash off any spills or splashes with plenty of water. Cover the fender and surrounding areas with rags or towels if you’re concerned about damage.
- Use a power bleeder: For stubborn air bubbles, a power bleeder canister that pressurizes the brake fluid can be a big help. Fill the canister with fresh fluid, pump it up to 15-20 psi, and connect the bleeder hose to the brake bleeder screws. This method simplifies the process, particularly on vehicles with multiple bleed points.
- Keep the master cylinder full: Always keep an eye on the master cylinder fluid level. If it runs low during bleeding, air will be drawn back into the system, requiring you to start over.
- Perform a brake pedal check: If the pedal feels soft or has too much travel after bleeding, there may still be air in the system or another issue. Perform a thorough check or consult a professional mechanic.
- Consult your service manual: Vehicle models and brake systems can vary significantly. Always refer to your vehicle’s service manual for specific instructions and recommended procedures for your make and model.
Conclusion
Bleeding your car’s brakes is a critical maintenance task that ensures your vehicle’s braking system performs safely and efficiently. With the right tools, a little patience, and some careful attention to detail, you can tackle this job yourself and enjoy the satisfaction of a job well done. Always follow safety precautions and consult your vehicle’s manual if you have any doubts.
Remember, if you’re ever unsure or uncomfortable with any part of the brake bleeding process, it’s best to seek help from a professional mechanic. Proper brake maintenance is vital for safe driving, so make sure your brakes are always in top shape. Happy driving!