How To Flush and Replace Brake Fluid

Updated: Mar. 29, 2024

Brake fluid goes bad. Flushing old brake fluid and replacing it with new keeps your brakes working safely.

Next Project

60–90 minutes




$40 to $60


After working as a General Motors and Automotive Service Excellence (ASE) certified master technician, I transferred those skills into a new career — teaching! I spent 25 years instructing the next generation of automotive service professionals at a local vocational high school. It was the hardest yet absolutely the best job I ever had.

Brakes and braking systems were a huge part of my curriculum. Here's a story I told my students: Once while working in a repair shop, I had to rebuild a set of brake wheel cylinders. The insides of the cylinders were filled with rust and muck. The debris etched the cylinder walls, damaging the inner cup seals. This caused them to leak, sending the brake pedal to the floor.

All those years ago, I didn't understand brake fluid is extremely hygroscopic, meaning it can absorb and hold moisture.

How does moisture enter a sealed brake system?

A small vent in the master cylinder prevents brake system vapor lock, which could seriously affect braking performance. The vent allows air into the reservoir as the brake fluid level drops when stepping on the brake pedal, then exits when stepping off the pedal. Air entering the master cylinder contains moisture, dust and dirt that contaminates the fluid.

Moisture in brake fluid causes metal brake parts to rust and corrode from the inside out (aka a rotted-through brake line). It also causes rubber parts to swell, deteriorate and weaken. Rust and corrosion floating in the brake system can clog up and ruin expensive anti-lock brake system (ABS) pumps and valves.

Can I flush brake fluid myself?

Yes. Although enlisting a helper makes flushing brake fluid easier, if you're comfortable safely jacking up a car and taking off wheels, you can flush the entire brake fluid system yourself.

Flushing brake fluid sort of like bleeding brake fluid. Bleeding the brakes removes air bubbles from the system. Air bubbles compress, causing a spongy or soft brake pedal or brake pedal fade. Flushing brake fluid removes all the old fluid and replaces it with new. Here's how to do it.

Special thanks to the administration and automotive technology program at North Montco Technical Career Center in Lansdale, Pennsylvania, for assistance with this article.

Tools Required

  • 3/8-in. breaker bar (optional)
  • 6-point or brake bleeding wrenches
  • 6-point sockets (optional)
  • Brass or plastic hammer (optional)
  • Creeper or mechanics roller stool
  • Drain pan
  • Fender cover
  • Floor jack
  • Hand vacuum pump brake bleeder kit
  • Jack stands or car ramps
  • Lug wrench or impact gun with sockets
  • Safety glasses
  • Torque wrench
  • Trouble light
  • Turkey baster
  • Wheel chocks

Materials Required

  • Brake fluid - two quarts (check your owner's manual or with your parts store for the correct type of brake fluid for your vehicle - never mix different types of brake fluids)
  • Brake fluid test strips or brake fluid pen tester
  • Disposable gloves
  • Disposable shop towels
  • Recycling bottle
  • Rust penetrator
  • Spray brake cleaner
  • Zip ties (optional)

Project step-by-step (9)

Step 1

Getting started

  • Put on your gloves and eye protection.
  • Gather all your tools and materials.
  • Install the fender covers to protect the paint finish.
  • Clean any dirt or grime off the master cylinder reservoir cap with the shop towels.
  • Use brake fluid test strips or a pen tester to measure brake fluid quality, condition and color. Old or contaminated brake fluid will be dark brown or may contain black gritty particles. New brake fluid is clear, with a subtle yellow to light brown tint.
  • Brake fluid is caustic. If using a brake fluid pen tester, carefully clean all the fluid from the contacts after use.

Safety note: If you spill brake fluid on your skin, paint, wires or any car parts, flush with plenty of water. Seek immediate medical attention if brake fluid splashes in your eyes, or if you accidentally swallow even the slightest amount.

Test Brake Fluid Condition W Test StripBob Lacivita for Family Handyman

Step 2

Change brake fluid in the master cylinder

  • Use the turkey baster to remove as much fluid as possible from the master cylinder reservoir. Brake fluid can damage the baster’s rubber bulb, so don’t suck the fluid all the way into it.
  • Don’t fully empty the reservoir or you will introduce air into the brake hydraulic system.
  • Squirt the old fluid into the recycling bottle.
  • Refill the reservoir to the “full” mark with new brake fluid from a sealed container.
  • Place the cap back on the new brake fluid bottle.
  • Properly dispose of the old fluid.

Pro tips: Brake and power steering fluids are incompatible, so use a different baster for each. Needless to say, never reuse those basters for food.

You can stop here, but why?

  • Stopping at this step (for beginners) leaves virtually the entire system full of contaminated brake fluid.
  • Continuing with this project (for advanced DIYers) will completely flush all the old fluid.
  • If you continue, fill the reservoir almost to the top.
  • Cover, but do not seal, the master cylinder opening to keep out dust and dirt.

Using A Baster To Suck Fluid Out Of The Master CylinderBob Lacivita for Family Handyman

Step 3

Determine the proper sequence for flushing the brake system

You may need a service manual to locate this information. Always start flushing the system at the wheel farthest from the master cylinder.

For rear-wheel-drive vehicles, do it in this order:

    1. Passenger rear wheel;
    2. Driver rear wheel;
    3. Passenger front wheel;
    4. Driver front wheel.

Sequence For Bleeding A Traditional Brake SystemFAMILY HANDYMAN

For front-wheel drive or diagonal split-brake systems:

    1. Passenger rear wheel;
    2. Driver front wheel;
    3. Driver rear wheel;.
    4. Passenger front wheel.

Sequence For Bleeding A Split Brake SystemFAMILY HANDYMAN

Note: It’s critical to follow the correct bleeding sequence for the type of brake system the vehicle has, to prevent introducing air into the brake fluid.

Step 4

Remove the wheel(s)

If you have ramps, sometimes you can open the brake bleeder valves with the wheels on. But this means lying on your back, which makes it particularly challenging. This is why we recommend removing the wheels and proceeding in this way:

  • Start on a flat smooth surface.
  • Fully engage the parking brake and place wheel chocks on the wheels opposite the end you’re lifting.
  • If using a lug wrench, loosen but do not remove the lug nuts from the wheel you’re flushing.
  • Carefully and safely jack up your vehicle.
  • Remove the lug nuts.
  • Remove the tire/wheel assembly(s) and move it off to the side.

Jack up your vehicleTMB Studio

Step 5

Preparing the brake bleeder valves

Pro tip: Don’t start trying to flush the brake fluid if the bleeder valve is frozen or seized in place by rust. To prevent water and road salts from rusting the valves in place, always replace or install bleeder valve protective covers.

  • Locate the brake bleeder valves on the disc brake calipers and wheel cylinders. They look like a grease fitting.
  • Remove the bleeder valve protective cover, if it has one.
  • Place a drain pan under the bleeder valve.
  • Clean away any dirt or gunk from around the bleeder valve with an old toothbrush, or brass brush and brake cleaner.
  • Spray the bleeder valve with rust penetrator and let it soak in for two or three minutes.
  • Use a six-point wrench or special brake bleeding wrenches you can borrow from your local auto parts store to loosen the valve. Bleeder valves are made from soft material, frequently dissimilar to the brake caliper/wheel cylinder, which can cause corrosion. A corroded bleeder valve can easily round over, or worse, snap off.
  • Using the palm of your hand, carefully “bump” the wrench — about as hard as you would a ketchup bottle — to loosen, but not open the bleeder valve. If you open the valve, air will enter the system.

Stop if the bleeder valve is frozen or rounded over. If this happens, it’s not the time to pull out your 20-volt impact driver. Here are a few techniques that may open rusted bleeder valves:

  • Use a deep six-point socket and hand impact driver to loosen the valve;
  • Or place a one-size-smaller deep six-point socket on the end of a 3/8-inch breaker bar. Lightly tap, do not pound, the top of the breaker bar with a brass hammer to carefully drive the socket onto the bleeder valve. Then, with slight pressure on the breaker bar, smack the top with a brass or plastic hammer to shock the valve loose. FYI: For this story, this is exactly what I had to do, and it worked like a charm.

If you’re unable to open the valve and there are no leaks, put your car back together and call your mechanic.

Brake Bleeder Hose On Bleeder Valve Held In Place W Zip TieBob Lacivita for Family Handyman

Step 6

Test the vacuum pump

Here, I used an inexpensive DIY-level brake bleeder vacuum pump kit. If you’re going to flush brake fluid on your friends’ and family’s cars, invest in a heavier duty pro level-kit.

Pro tip: There’s no reason to start flushing the system if the vacuum pump doesn’t work.

  • Do not use your finger to test the vacuum pump.
  • Slide the vacuum control collar forward toward the hose inlet fitting of the pump.
  • Insert a screw (or cap from a tube of caulk) into one of the supplied hoses. Slide the other end of the hose over the pump inlet fitting.
  • Operate the vacuum pump lever several times.
  • Look at the vacuum gauge to ensure the pump holds at least 15 inches of mercury for at least 30 seconds. Vacuum is measured in inches of mercury (Hg) on a scale of 0 to 30 inches.
  • Slide the control collar back toward the handles to release the vacuum.

Testing Vacuum Pump Holding VacuumBob Lacivita for Family Handyman

Step 7

Assemble the vacuum pump

  • Remove the cap with two inlets from the bleeder cup/reservoir, wipe the O-ring with fresh brake fluid.
  • Insert one of the short hoses into the port under the cap.
  • Add an inch of fresh fluid to the container to prevent air from being drawn back into the brake system.
  • Replace the cap. Be careful not to damage the O-ring.
  • Connect the long hoses to the two inlets on the cap.
  • Insert the correct-size bleeder valve adapter into hose inlet closest to the hose attached to the port on the underside of the cap. Attach the other hose directly to the vacuum pump.

Note: For the vacuum pump to work properly and draw fluid and air out of the brake system, the tube that connects to the fitting on the underside of the collection cup lid must be connected to the fitting/hose that connects to the brake bleeder valve.

How To Properly Assemble And Connect The Brake Bleeding Vacuum Tool 1FAMILY HANDYMAN

Step 8

Flushing the brake system

Now you’re ready to flush the brake fluid!

  • Follow the proper sequence for flushing the brake system (Step 3).
  • Prepare the bleeder valve (Step 5).
  • Push the bleeder valve adapter onto the bleeder valve. If connecting the hose directly to the bleeder valve, secure with zip ties if it keeps coming off.
  • Squeeze the vacuum pump handle until the vacuum gauge reads at least 10 inches of vacuum.
  • Open the bleeder valve.
  • Allow brake fluid to flow into the cup until the fluid runs clear and there are no air bubbles.
  • Securely retighten the bleeder valve.
  • Release the pump’s vacuum.
  • Remove the vacuum hose or adapter. Reinstall or replace the bleeder valve protective cover.
  • Refill the master cylinder with fresh fluid.
  • Clean up any spilled brake fluid.
  • When there are no air bubbles and only clear brake fluid comes out of the bleeder valve, move on to the next wheel and repeat the same procedure.
  • Once all four wheels have been flushed, add brake fluid to the master cylinder’s reservoir to the “full” or “max” mark. Do not overfill.
  • Reinstall the master cylinder cap. Replace the master cylinder cap gasket or seal if it’s mushy or distorted.
  • Reinstall the wheels and snug up the lug nuts.
  • Lower the vehicle. Use a torque wrench to tighten all lugs nuts to proper specification.
  • Test the brake pedal to make sure it feels normal before driving. Your brakes should respond quickly when stopping.
  • Check the bleeder valve for leaks. If you see fluid coming out of the bleeder, remove and reseat the valve, or replace the bleeder valve with a new one. Then follow the steps above to re-bleed that wheel.
  • If the pedal fades or doesn’t feel natural when stopping, bleed the brakes again or take your car to a pro.
  • Clean and dry all tools, including the vacuum pump, hoses and fittings, with a non-mineral-based cleaner. Then store in a safe, dry location.
  • Properly dispose of the old fluid.

Pro tips

  • When emptying the old brake fluid out of the system, don’t fill the cup more than three-quarters. The old fluid shouldn’t reach the top of the cup or enter the vacuum pump cylinder.
  • Keep the cup as level as possible during use.
  • The kit comes with an extra cup and lid without inlets to transport old brake fluid for disposal.
  • Any air entering the system means you have to start over, from the beginning.

Flushing Out Old Brake FluidBob Lacivita for Family Handyman

Step 9


New Brake Fluid Vs Contaminated Brake FluidBob Lacivita for Family Handyman

When should I call a pro?

Know your skill limits. Although you can save hundreds of dollars over the years flushing brake fluid yourself, this project is not for novice DIYers, especially if you lack the proper tools.

How do I know if my brake fluid is low?

Low brake fluid can cause any of these problems:

What causes low brake fluid?

The most common reasons include:

  • Worn disc brake pads. It’s normal for brake fluid levels to drop as brake pads wear.
  • A leak in any brake hydraulic circuit part (disc brake caliper, wheel cylinder, brake hoses or double-rolled steel brake lines).

Can I add new brake fluid to old?

Yes, but never mix different types of brake fluids. Only add new, fresh brake fluid, and be sure it’s the correct type for your car.

Is it necessary to change brake fluid?

Yes. Like other fluids in our vehicles, heat, pressure, temperature fluctuations, wear and tear and moisture cause additives in brake fluid to wear out or degrade. Brake fluid should be flushed every two years or 30,000 miles, whichever comes first.