How to Gravity Bleed Brakes

Do you know how to gravity bleed brakes? If you’re maintaining your own brakes, then you will have to bleed them at some point. It sounds a bit gruesome, but it’s really nothing more than draining out all the old brake fluid so it can be replaced with fresh fluid. Here’s what you need to know about how to gravity bleed brakes.

Why Do This?

All the fluids in your car need attention from time to time. You change your oil and check your coolant, right? Well, you need to bleed the brakes as well to make sure your brake fluid does its job. Be sure to follow the manufacturer’s recommendations regarding the proper intervals, whether it means bleeding the breaks every 20,000 miles or every 150,000 miles. This isn’t something you should skip, and you can bleed the brakes more often if needed. It’s a good idea anytime you’ve been working on the system and there’s a chance that air got into the lines.

The reason why this is important is that brake fluid is hygroscopic, which means it absorbs water from the air. That water lowers the boiling point of your brake fluid, and when it boils it can escape the lines as steam. You’ll feel this low fluid as a spongy brake pedal and see contamination as a black goo in the fluid reservoir. That goo is corrosive and can lead to the introduction of even more air into the system, creating a vicious cycle that ruins your brakes.

Safety First

Make sure you park your car on a level surface. You’ll need jack stands to lift it up and remove the wheels, and you’ll also need something to protect your hands. Brake fluid is caustic, so keep it off of your hands, clothes and any paint or finishes on your car, as it can cause damage. Make sure you have a plan to properly dispose of the old brake fluid. For instance, you could do a web search for hazardous waste disposal in your town. Do not dump it down a drain.

Start With the Master Cylinder

Begin the process by popping the hood, locating the master cylinder and removing most, but not all, of the brake fluid from it with a turkey baster, siphon or similar device. The key here is to leave some fluid behind. Do not bleed the master cylinder dry. Next, add fresh fluid and cap the bottle immediately after to keep the air out.

Move to the Brakes

Start with the brake furthest from the reservoir. Attach one end of a small hose to the brake bleeder bolt, and put the other into a bottle with a little clean fluid at the bottom so no air gets sucked back into the system.

Now it’s time to let gravity do the work. Open the bleed screw and you’ll see dirty fluid slowly flowing into the bottle. Once the fluid runs clean, you’re all set and can move on to the next brake. This might take up to an hour for each wheel. While it might not be the quickest job, the effort is minimal and the majority of the time is spent waiting. You don’t want to run the reservoir dry as you bleed, so top it off between each wheel. Repeat this process for each of your brakes. Once you’re done, top off the reservoir to the fill and replace the cap. Now you can reassemble your brakes and reinstall the wheels.

It’s easy to gravity bleed brakes. Make sure you do this anytime you work on your brakes and expose air to the system — or at least at the manufacturer’s recommended intervals to keep your brakes working properly.

Check out all the brake parts and brake care products available on NAPA Online, or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information about how to take care of your brakes, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy Flickr.