Normally, you want to avoid bleeding. Unless you’re cleaning your prey or making a voluntary visit to the Red Cross, opening veins and arteries is best avoided. But one system you want to bleed like an 18th century doctor is your brake system.
Most modern brake systems are hydraulic, which means they use fluid pressure to move the pads and/or shoes. But over time, air begins to seep into that system. At first, it’s merely an inconvenience, softening up your brake pedal and reducing its responsiveness. Eventually, however, enough air in your system could mean the difference between stopping by yourself and letting the trees, buildings, and other cars help you.
To get that air out of your lines is a fairly simple process called Brake Bleeding. Here’s what you need to do.
Fill the can. Locate your master brake cylinder under the hood. Look for the lids that seem to go on and on about only using DOT approved brake fluid. The bigger one will be your master cylinder. Pop off that cap and fill it with brake fluid until the level sits pretty ¼” from the top.
Prep the valves. To each of your brake calipers is fitted a bleeder valve specifically for this purpose. Take a can of penetrating oil around the car and spray a little on each of the valves. Let that sit for a while and work its magic.
Bleed each valve. Start with the wheel furthest from the master cylinder. It’s usually the rear right wheel. Press a length of clear plastic tubing onto the bleeder valve and put a jar under the other end to catch the brake fluid. Next, have a friend, spouse, or family pet depress the brake pedal, and with he/she/it keeping up the pressure, loosen the valve. Brake fluid should shoot out like an ex-president from the spotlight. The brake pedal will slowly retreat all the way to the floor. When it has, tighten down the bleeder valve again and have your buddy let go of the pedal. Repeat.
The whole time, keep an eye on the fluid as it exits the valve. You should be able to see any bubbles in the system, and after a few pumps, when the foam is gone as from a flat A&W, all the air has been purged from that branch of the system. Keep in mind that the fluid you’re shooting out of the lines is coming from that master cylinder, so after each valve is bled, you’ll want to keep the level up. Work your way around the car, from the wheel furthest from the master cylinder to the wheel closest, repeating the process.
And you’re done, son. That’s about it. Make sure you replace the cap on the master cylinder and lock it down tight. As a precaution, take your first drive afterward around a low-speed-limit area, with your handbrake at the ready.
Bleeding your own brakes, rather than having the pros do it, can save you a fat stack of cash in service charges. Plus, the next time a friend/mother/damsel in distress has a spongy brake pedal, you get to be the hero. And every good hero knows how to bleed.