How to Flush Brake Fluid

Oil changes. Transmission and Antifreeze changes. Air filter intervals. If you've been working around cars long enough, you've heard constant reminders about when to change what, and how often. There is a fluid though that often goes ignored entirely - and when it does - bad things are soon to happen. We're talking about brake fluid. It's operates the system on everyone's car that saves their life every time they use it - the brakes!

Why Does Brake Fluid Wear Out?

Brake fluid, a hydraulic fluid, by its chemical design is hygroscopic, which means it absorbs water at a rapid rate. This presents problems in any brake system as the master cylinder, lines, proportioning valves, ABS system, and calipers are all composed of parts made from aluminum or steel, metals that corrode in water! Brake fluid is arguably the most ignored fluid change on your car, with some cars going all the way to brake component failure until the component is changed and fluid is flushed. Don’t let it get that far!

Any time the brake system is exposed to any air (usually from the master cylinder reservoir), the fluid absorbs moisture, and as it does so, it’s color turns from clear to a rusty brown over the course of thousands of miles, as corrosion begins inside the brake system. The more water in the fluid, the lower the brake fluid boiling point becomes (think of how hot brakes operate) and the more corrosive the fluid gets. Corrosive brake fluid is the #1 reason why calipers and wheel cylinders begin to seize, as corrosion inside the bores of the cylinder occurs from the contaminated fluid.

What’s a Brake Fluid Flush?

Here enters the brake fluid flush. A car owner who can proactively flush their brake fluid every time a set of pads or shoes is/are installed on their car (usually every 35-60K miles) reduces the risk of brake fade and future caliper or wheel cylinder failure, and they will get overall better brake performance.

Performing a brake fluid flush is an easy task, like changing oil. Before anything, be sure to always make sure to read who to properly bleed the brake system by doing a 2-person brake bleed. If you are unsure, you can always take your car to your preferred mechanic and ask for the fluid to be flushed.

If you are familiar with how to bleed brakes, you will be performing this process the same way as when you change a caliper, brake line, or wheel cylinder. This process is best done by a simple 2-person brake bleed – one person operating the pedal and holding, while the other opens the bleeder screw for less than 2 seconds. You will also need a quart of your favorite brand, and type of brake fluid (remember to check whether the car takes DOT 3 or DOT 4 fluid).

How to Flush and Change Brake Fluid

1. Empty the Master Cylinder Reservoir

The first step is to completely remove all the fluid that’s currently sitting inside the master cylinder reservoir. This can be done a number of ways, but a large syringe, turkey baster, small siphon pump, or transfer pump and tube can easy remove all the fluid from the reservoir while the car is off and in park, with no pressure on the brakes.

2. Fill and Bleed

Next, fill the reservoir with fresh fluid. From here on out, the process is no different than bleeding brakes. Having a small, 2 foot section of clear tubing to fit over the bleeder screw makes the process easy to see when the old fluid has all been removed.

Simply start at the rear of the car first, and bleed out the 2 rear calipers/wheel cylinders. You will know when the old fluid has all been removed when the rusty, brown fluid is gone and fresh, clear fluid is flowing through the tube.

Then, move on to the fronts, being sure to re-check the master cylinder reservoir after each wheel is bled.

3. Top It Off

After your last wheel, fill the reservoir back to the fill line and you’re done!

How Often Should You Change Your Brake Fluid?

That is a great, and often debated question because it’s one of the few fluids that car manufacturers do not normally set a change interval. A good practice though is every 3 years or 30,000 miles.

You can find everything you need to flush your own brake fluid at any of our AutoZone stores. Stop by and talk to a store associate to find all of the parts and tools you need to get the job done right. Or, if you are not the mechanical-type, consider bringing it to one of our Preferred Repair Shops in your area.

Advice, how-to guides, and car care information featured on and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.

Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.

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