Brake Bleeding….

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Bleeding brakes can be done several ways. The traditional two-man method requires one person to depress the brake pedal to the floor while the other opens a bleeder valve (there’s one at each wheel) to let the old fluid (and air bubbles) escape. Before the pedal is allowed to rise to its normal position, the second person must close the bleeder valve to prevent air from being sucked back in.

This process is repeated several times until all the air is gone.

During the process, the master cylinder must be kept topped off with fluid; otherwise, it can run dry and then you’ll just suck air into the system that way. Maintain the level at the “full” mark as you proceed.

Also: Don’t mash the brake pedal; ease it up and down gently or else brake fluid will splash everywhere. It’s smart to cover the fender near the master cylinder with a rubber mat; something that won’t let any spilled fluid seep through to contact the paint. If you do accidentally spill any brake fluid on painted surfaces, stop what you’re doing and clean it up immediately. Brake fluid will eat through the paint if you don’t. A spray-can detailer such as Honda Clean (http://www.amazon.com/Honda-Spray-Cl…/dp/B00383T62O) can save your car’s finish. Keep it handy.

Some mechanics like to attach a hose to the bleeder valve they’re working on, with the other end immersed in a container filled with brake fluid. This way, they can actually see the air bubbles — and when they stop coming.

This method also makes less of a mess, since you capture all the old fluid in your container instead of it squirting all over the floor.

Just be careful not to suck old fluid (and air bubbles) back into the system.

Do one wheel at a time; never open more than one bleeder valve at once.

Once you’ve purged all the trapped air from one wheel, move on to the next and repeat.  Important: Bleed the wheels in pairs – first the fronts then the rears. (Each set is paired and has its own separate fluid reservoir within the master cylinder.) The brake pedal should get firmer as air is removed from the system.

When all four have been bled, you no longer see any air bubbles coming out and the pedal feel is normal again, the job is done.

Work carefully and take your time. Getting out all the air is really important. If you don’t, the brakes will feel soggy and the car could be dangerous to drive. Air can be compressed; fluid can’t. This is why the pedal will feel soggy if there is air still in the system.

What if you don’t have a buddy to help you do the job? One possibility is gravity bleeding. This Old Mechanic’s Method works but takes a little more time, a little more patience  – and more brake fluid than you’d otherwise need.

Here’s the theory: The master cylinder, which contains the reservoir holding the brake fluid, sits higher up than all four wheels. If you fill the reservoir with fluid and then crack open the bleeder screws do one at a time)  the force of gravity will cause the fluid in the reservior to slowly drain out – forcing any trapped air out along with it.

The only catch here is to be sure you watch the fluid level in the reservior and keep it topped off before it empties out. (This is why you’ll use more brake fluid than if you and a buddy bled the system the regular way.) If you don’t and it gets too low, air will be sucked into the system, and it’s back to square one.

Caution: This technique won’t work on ABS-equipped cars, which need special equipment for bleeding.

Do the front brakes first, then the rears. Run about two pints through the system and you will usually have gotten rid of any trapped air and be ready to roll.

When you’re finished, close the bleeder valves snugly (not too tight – they’re easy to break) and put a rubber nipple or vaccum cap over each one to protect it from rusting and to keep dirt from getting into the orifice.

Vacuum caps can be purchased for less than $5 a pack at any auto parts store.

Another helpful tool for one-man brake work is Speed Bleeders (http://www.speedbleeder.com/). These puppies have an internal one-way check valve that lets fluid out, but doesn’t let air back in. You just crack ’em open and work the brake pedal until all the air is purged from the system. Speed Bleeders replace the factory bleeder screws and install in minutes.

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1 COMMENT

  1. Dood, another thing I do before I get the party started is drain all the fluid from the master cylinder (don’t go completely crazy though). Then I add new fluid in there and top it off as necessary while bleeding. When I have the system open I figure brake fluid is cheap and the job is easy, so why not just change all the fluid. Some other advice, this is something a lot of people neglect, wear safety glasses! I am forced to wear glasses anyhow because my vision sucks. Break fluid in the eye is not fun. Also, purchasing a small siphon pump makes the job a lot easier for draining the master cylinder and can also be used to drain your power steering fluid and clutch reservoir. Around $10. Also, use the box end on your wrench to crack the bleeder. There is nothing worse than leaving that (rounded bolts/nuts) signature behind on a job. The only signature you should leave is the look of a brand new, or clean looking part/area (this is true for any repairs). Pu..pu..pump it up, holding..

    Siphon Pump

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