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Auto Repair: Bleeding Your Brakes

Working on a creeper

If your vehicle has squishy-feeling brakes, the way to get the air out of the lines is to bleed the brakes. To do the job, you need either a brake bleeder wrench or a combination wrench that fits the bleeder nozzle on your vehicle, a can of the proper brake fluid, a clean glass jar, and a friend.

Caution: To avoid getting air into the actuator of ABS, EBD, BA, or other sophisticated brake systems, a professional should bleed the brakes for you.

Follow these steps to bleed your brakes:

  1. Find the little nozzle called a brake bleeder screw (see Figure 15-9) that's located behind each of your brakes.

    Reaching this bleeder screw may be easier if you jack up the vehicle. If you're going to crawl underneath, lay down an old blanket or a thick layer of newspapers first. If you really want to be comfortable, beg or borrow a creeper to lie on and slide around with easily.Figure 15-9: Using a bleeder hose to bleed your brakes.

  2. Special wrenches called bleeder wrenches fit the bleeder screw and can prevent rounding the screw's hex-head. Find the proper wrench or socket that fits the screw, and loosen the screw.

    Be careful not to break the screw off or you'll need professional repairs. If it's stuck, spray some penetrant like WD-40 around the screw. After you loosen the screw, tighten it again (but not too tight).

  3. If you have a small piece of flexible hose that fits over the end of the bleeder screw, attach it and place the end of the hose in the jar. Then fill the jar with brake fluid to cover the end of the hose (see Figure 15-9). If you don't have anything that fits over the bleeder screw, just keep the jar near the nozzle so that any fluid that squirts out lands in the jar.
  4. Have your friend slowly pump your brake pedal a few times (see Figure 15-10). Have your friend say "Down" when pressing the brake pedal down and "Up" when releasing it.

    Caution: If the vehicle is jacked up, before you let your friend get into it with you underneath it, make sure that the wheels are blocked in the direction in which the car would roll and that it isn't parked on a hill. Leave your tires in place so that the vehicle will bounce and leave you some clearance if it falls.Figure 15-10: How to bleed your brakes.

  5. When your friend has pumped the pedal a few times and is holding the pedal down, open the bleeder screw.

    Brake fluid will squirt out (duck!). If there's air in your brake lines, air bubbles will be in the fluid. Seeing these bubbles is easiest if you're using the hose-in-the-jar method, but you can also see them without it.

  6. Before your friend releases the brake pedal, tighten the bleeder screw.

    If you don't, air is sucked back into the brake lines when the pedal is released.

  7. Tell your friend to release the pedal, and listen for him or her to say "Up." Then repeat Steps 2 through 6, loosening the screw and tightening it again and again until no more air bubbles come out with the fluid.
  8. Open your master cylinder and add more brake fluid until the levelreaches the "Full" line.

    Caution: If you neglect to do so, you run the risk of draining all the fluid out of the master cylinder and drawing air into the lines from the top. If that happens, you have to go back and bleed your master cylinder until you suck the air out of that end of the system. Who needs the extra work?

    If you goof and have to bleed the master cylinder, it's the same deal as bleeding your brakes (friend and all). Just bleed it at the point where the brake lines attach to the cylinder or at the master cylinder's bleeder nozzle if you have one (see Figure 15-11).Figure 15-11: Bleeding a master cylinder: If you have a bleeder nozzle, use the hose and jar method (a). If not, bleed the cylinder at the brake line connections (b).

  9. Remember: Repeat Steps 2 through 8 with each brake until the air is out of each brake line. Don't forget to add brake fluid to the master cylinder after you bleed each brake.
  10. After you finish the job and bring the brake fluid level in the master cylinder back to the "Full" level for the last time, drive the vehicle around the block.

    The brake pedal should no longer feel spongy when you depress it. If it does, check the master cylinder again to be sure that it's full, and try bleeding the brakes one more time (this situation isn't unusual, and it doesn't take as long as it sounds).

Tip: If you know that no air is left in the brake lines but the brakes still don't feel right, you may need a new master cylinder. Unless you have one of the few Japanese vehicles that integrate the ABS actuator in the master cylinder, you should definitely consider installing it yourself — at an auto class. All it involves is disconnecting the old master cylinder (a bolt or two and the hoses leading to the brake lines), removing it without spilling brake fluid on anything painted, installing the new one, filling it with brake fluid, and bleeding it. If your vehicle has ABS, the new fluid is pumped through the actuator as well as the master cylinder when you bleed the system, using up a bit more brake fluid than bleeding a non-ABS system, so plan ahead and buy an extra can or two.

If the job seems like too much of a hassle, have a professional do the work. You shouldn't have to pay for much labor, and if you choose a brake shop wisely, the whole deal shouldn't cost too much. Whatever you do, just be sure that when the job is finished, they (or you) bleed the brakes and themaster cylinder to get all the air out of the lines.

True Story: When I bought Tweety Bird, my first car, I had her master cylinder replaced professionally for about $60. (It would cost sooo much more now!) A few months later, I helped a friend replace a master cylinder with a rebuilt one. The rebuilt master cylinder cost about half of what I'd paid for a new one, and there were no labor charges (naturally). What are your time and troubleworth to you?

From Auto Repair for Dummies, copyright © 2009 by Wiley Publishing, Inc., Indianapolis, Indiana. Used by arrangement with John Wiley & Sons, Inc.

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