How to Replace Brake Fluid：Six simple steps and three methods

That spongy feeling in your brake pedal? The slightly longer stopping distances? These could be subtle cries for help from your car’s braking system. The culprit is often old, contaminated brake fluid. While it might sound like a job for a mechanic, replacing your brake fluid is a manageable DIY task that can save you money and, more importantly, ensure your brakes are in top condition. This guide will walk you through everything you need to know, from why it’s crucial to the step-by-step process.

Why Bother Changing Your Brake Fluid?

Brake fluid is hygroscopic, which is a fancy way of saying it absorbs moisture from the air over time. This moisture has two negative effects:

• Lowers the Boiling Point: As water content increases, the boiling point of the brake fluid drops. The braking process generates a lot of heat. If the fluid boils, it creates air bubbles in the brake lines. Air is compressible, while fluid is not. This means when you press the brake pedal, you’ll be compressing air instead of applying force to the brakes, leading to a “spongy” or soft pedal and a dangerous loss of braking power.
• Causes Corrosion: The moisture can cause rust and corrosion in your brake lines, calipers, and master cylinder. This can lead to expensive repairs down the road.

Most vehicle manufacturers recommend replacing your brake fluid every two to three years, but it’s always best to consult your owner’s manual for the specific interval for your car.

Signs It’s Time for a Brake Fluid Change

• Spongy or Soft Brake Pedal: This is the most common symptom.
• Increased Stopping Distance: If you notice your car is taking longer to stop than usual.
• ABS Light is On: In some cases, contaminated fluid can affect the Anti-lock Braking System.
• Dark or Cloudy Fluid: New brake fluid is typically a light amber color. If yours looks dark, murky, or has particles in it, it’s time for a change. You can check this by looking at the brake fluid reservoir.

Getting Started: What You’ll Need

Before you get your hands dirty, you’ll need to gather a few essential tools and supplies.

Tools & Materials:

A Word on Brake Fluid Types:

It is critical to use the correct type of brake fluid specified for your vehicle. Using the wrong type can damage your braking system.

• DOT 3 and DOT 4: These are glycol-based and are the most common. DOT 4 has a higher boiling point than DOT 3. You can usually substitute DOT 4 for DOT 3, but not the other way around.
• DOT 5: This is silicone-based and should never be mixed with DOT 3 or DOT 4 fluids. It’s typically used in classic cars or military vehicles.
• DOT 5.1: This is also glycol-based and has a higher boiling point than DOT 4. It can be mixed with DOT 3 and DOT 4.

Always check your owner’s manual or the cap of the master cylinder reservoir for the correct fluid type.

The Brake Bleeding Process: Step-by-Step

Brake bleeding is the process of pushing the old, contaminated fluid out of the system while introducing new, clean fluid. Here are three common methods to do it.

Preparatory Steps (For All Methods)

1. Safety First: Park your car on a level surface and engage the parking brake.
2. Lift the Vehicle: Loosen the lug nuts on your wheels before jacking up the car. Then, use a jack to lift the vehicle and secure it with jack stands. Never work under a car supported only by a jack.
3. Remove the Wheels: Take off the wheels to get access to the brake calipers and their bleeder screws.
4. Locate the Master Cylinder: Open your hood and find the brake fluid reservoir. It’s usually a small, translucent container on the driver’s side.
5. Remove Old Fluid: Use a turkey baster or syringe to suck out as much of the old brake fluid from the reservoir as possible. Do not empty it completely. Wipe out any gunk from the reservoir with a clean, lint-free cloth.
6. Fill with New Fluid: Top up the reservoir with new, clean brake fluid. Keep the master cylinder cap off but cover the opening to prevent dirt from getting in. Throughout the process, keep a close eye on the fluid level in the reservoir. If it runs dry, you will introduce air into the system, and you’ll have to start over.

Method 1: The Two-Person Method (The Classic)

This is the most common and reliable method for DIYers.

1. Start at the Correct Wheel: The bleeding sequence is important. You should start with the brake furthest from the master cylinder and work your way closer. For most cars with the master cylinder on the driver’s side, the sequence is:
   • Right Rear
   • Left Rear
   • Right Front
   • Left Front
2. Attach the Tubing: Locate the bleeder screw on the brake caliper. It’s a small nipple-like valve. Place your wrench over it, and then attach the clear tubing to the end of the screw. Put the other end of the tubing into your catch bottle.
3. The “Pump and Hold” Dance: This is where your helper comes in.
   • You: “Pump the brakes.”
   • Helper: Pumps the brake pedal slowly three to five times and then holds it down firmly. They should call out “Holding!”
   • You: While your helper is holding the pedal down, open the bleeder screw about a quarter to a half turn. Old fluid and air bubbles will flow out.
   • You: Close the bleeder screw just before the fluid flow stops.
   • You: “Release the brakes.”
   • Helper: Releases the brake pedal.
4. Repeat and Refill: Repeat this process until you see clean, new fluid with no air bubbles coming through the clear tubing. Remember to top up the master cylinder reservoir with new fluid every four to five cycles.
5. Move to the Next Wheel: Once you’re done with one wheel, tighten the bleeder screw (don’t overtighten it), remove the tubing, and move to the next wheel in the sequence.
6. Final Check: After all four wheels are done, top up the master cylinder to the “Max” line and replace the cap. Pump the brake pedal a few times. It should feel firm.

Method 2: The Gravity Bleeding Method (Slow and Steady)

This method is simpler but takes much longer. It’s a good option if you’re working alone.

1. Get Set Up: After the initial prep, simply attach the clear tubing to the bleeder screw of the first wheel and place the other end in the catch bottle.
2. Open the Bleeder Screw: Open the bleeder screw about a half turn.
3. Wait: Gravity will do the work, slowly dripping the old fluid out. This can take a while, so be patient.
4. Monitor the Reservoir: Keep a very close eye on the master cylinder and top it up with new fluid as needed. Do not let it run dry.
5. Look for Clean Fluid: Once you see clean fluid dripping out, close the bleeder screw.
6. Repeat for All Wheels: Move on to the next wheels in the correct sequence.

Method 3: The Vacuum Pump Method (The Pro’s Choice)

A vacuum pump makes the job quicker and is a great one-person solution.

1. Connect the Pump: Attach the vacuum pump’s tubing to the bleeder screw.
2. Create a Vacuum: Pump the handle to create a vacuum in the line.
3. Open the Bleeder Screw: Slightly open the bleeder screw. The vacuum will suck the old fluid out.
4. Watch the Fluid: Keep an eye on the fluid color and look for air bubbles. Continue until the fluid runs clear.
5. Maintain the Vacuum and Fluid Level: You may need to pump occasionally to maintain the vacuum. As always, keep the master cylinder topped up.
6. Close and Repeat: Close the bleeder screw before releasing the vacuum to prevent air from being sucked back in. Repeat for the other wheels.

Comparison of Brake Bleeding Methods

Finishing Up

Once you’ve bled all four brakes:

1. Double-Check Bleeder Screws: Make sure all bleeder screws are snug.
2. Reinstall Wheels: Put your wheels back on and tighten the lug nuts in a star pattern to the manufacturer’s recommended torque.
3. Test the Brakes: Before you go for a drive, start the car and pump the brake pedal. It should feel firm and high.
4. Dispose of Old Fluid: Brake fluid is hazardous waste. Take it to an auto parts store or a local recycling center for proper disposal. Do not pour it down the drain or on the ground.

Frequently Asked Questions (FAQs)

Q: How much does it cost to have a mechanic replace my brake fluid? A: Typically, a professional brake fluid flush can cost anywhere from $100 to $200, depending on your vehicle and location. Doing it yourself can save you a significant amount of that.

Q: How long does it take to replace brake fluid? A: With the two-person or vacuum pump method, it can take about an hour for an experienced DIYer. If it’s your first time, allow for a couple of hours. The gravity method can take several hours.

Q: Can I just top off my brake fluid? A: If your brake fluid is low, you can top it off to get by in an emergency. However, low fluid usually indicates a leak or worn brake pads. Simply topping it off doesn’t remove the moisture and contaminants, so it’s not a substitute for a full replacement.

Q: What happens if I don’t change my brake fluid? A: Over time, the moisture-laden fluid can lead to a soft, spongy brake pedal, reduced braking performance, and eventually, brake failure. It can also cause expensive corrosion to your braking system components.

Q: Can I mix different types of brake fluid? A: You can generally mix DOT 3 and DOT 4, but it will lower the boiling point of the DOT 4 fluid. You should never mix DOT 5 (silicone-based) with DOT 3, DOT 4, or DOT 5.1 (glycol-based) fluids. Always use the type of fluid recommended in your owner’s manual.

By taking the time to replace your brake fluid, you’re not just performing routine maintenance; you’re investing in your safety on the road. With a little patience and the right tools, you can confidently tackle this job and keep your braking system in prime condition. Happy motoring!