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How to bleed your brakes

How to bleed brakes – the right way
MSF Comeskey by John and James Walker, Jr., scr motorsports

Why Bleed brakes?

The term "bleeding the brakes" refers to the process which opens a small valve on the caliper (or wheel cylinder) to allow controlled amounts of brake fluid to escape from the system. (When one thinks it, "bleeding" may appear to be a somewhat graphic term, but it aptly describes the release of a vital fluid.)

We bleed the brakes to release air that sometimes becomes trapped within the lines. Technically, "air" only enters the lines if there is a commitment system sealing (as when the flexible lines are removed or replaced), because when the liquid boils, it will instead create "fluid vapor." Vapor in the Brake fluid, like air, will create a loss of efficiency in the braking system. However, for the sake of simplicity we use the term "air" through this article to describe both air and steam flow.

When the air (or vapor) is present within the lines, it creates inefficiencies in the system because, unlike liquid, air can be compressed. So when the air fills enough lines to enter the pedal simply makes the air to compress instead of creating pressure on the corners of the brakes. In other words, when air is present in the system, the efficiency and effectiveness of the braking system is reduced. Usually, a small amount of air in the brake system will contribute to a soft "or" soft "pedal (since less energy is needed to compress the air needed to move the fluid along the brake lines.) If enough air enters the brake system, which can lead to complete brake failure.

So how to write the airlines in the first place? Sometimes it may be the result of a service procedure or an upgrade – as replacement of the population of flexible lines braided stainless steel lines. But often it is the result of high temperatures that cause brake fluid components to boil, thus releasing gases boiling liquid into the hydraulic brake system.

Selection of brake fluid

This leads us to contemplate the type of liquid used as brake fluid. In theory, even plain water would work – and that, if a liquid, water can not be compressed. However, it is important to remember that the fundamental function of the braking system is to convert kinetic energy into heat energy through friction. And the reality of this process is that certain parts of the braking system will be exposed to very high temperatures. In fact, it is not uncommon to see temperatures of the rotor during a career as high as 1,200 degrees Fahrenheit – which can raise the temperature of the brake fluid to over 300 degrees Fahrenheit. Since the boiling point of water is 212 degrees Fahrenheit, it is easy to see that the water inside the brake system could boil easily – and therefore release gases into the brake pipes – which would reduce the efficiency the system. (Water would also present a major problem in cold climates when frozen in ice!)

The "obvious" solution to this problem is to use a liquid that is less sensitive to extreme temperatures. Hence the development of "brake fluid." But unfortunately no such thing as a "Perfect" brake fluid. And like most things in the world, the addition of certain beneficial characteristics usually brings advantages and disadvantages in other areas. In the case of brake fluid, usually has to balance the fluid temperature sensitivity of their cost and impact on other components within the system.

Simply put, it is possible to reduce the sensitivity of an oil temperature to vary the ingredients of the fluid. However, certain combinations of ingredients can significantly increase the cost of the fluid and may react with OEM materials to damage seals and induce corrosion throughout the braking system.

The chemical composition and minimum performance requirements of the fluid are usually indicated by a classification as "DOT3" DOT4 "or" DOT5. "DOT-rating itself is assigned after a series of government tests. However, this characterization is not intended to indicate boiling points, even though higher DOT ratings generally correspond with higher boiling points. Perhaps most important, the DOT rating indicates the base compound brake fluid – which allows manufacturers to specify types of liquids that are less likely to react negatively to the materials known and used within a particular braking system.

The greatest irony regarding brake fluid, however, is the fact that the chemical compositions which tend to be less sensitive to extreme temperatures tend to attract and absorb water! So although the fluid itself is unlikely to boil (liquid DOT 3 more glycol based have a "dry boiling point" around 400 degrees Fahrenheit), water absorbing time it tends to boil with ease (at 212 degrees Fahrenheit.) It is this characteristic of absorbing moisture that leads to the measure known as the "wet boiling point." Wet Boiling Point is the equilibrium boiling point of liquid after the absorption of moisture, under specified conditions. Because Brake fluid absorbs moisture through of the brake system hoses and reservoir, evaluation of the wet boiling point is used to test the performance of used brake fluid and degradation in performance. (And that's why we still need to bleed the brakes often in racing cars, even though racing use liquid that costs upward of $ 75 per bottle!) The lesson: do not expect to avoid bleeding the brakes just because you bought expensive brake fluid.

As one can imagine, "racing" fluid use relatively "aggressive" chemical compositions that tend to have higher wet boiling points and higher costs, while the middle of the street used fluid compositions are more conservative than lower wet boiling points and lower costs. In some cases – like a race car built especially – the compensation for racing using the liquid side is offset by competitive advantages. But for the average driver – whose driving style is less likely to induce brake temps as high as those seen on the track – the cost of fluids and potential wear-and-tear factors in the components of the system can justify the use of a fluid more conservative with a lower wet boiling point.

How-To

Therefore, now you understand the need behind bleeding the brakes, we present a simple procedure that can be used to maintain your own car. Note that unless you are replacing your master cylinder, the procedure is the same whether you have a vehicle equipped with ABS or not …

Materials required

You will need the following tools:

• Box suitable wrench to bleed screws for your car. An offset design head usually works best.
• Extra brake fluid (about 1 pint if you are bleeding, about 3 if completely replacing).
• 12-inch long section of plastic tubing, ID size to perfectly fit the screws vent of your car.
• Disposable bottle for waste fluid.
• A can of brake cleaner.
• An assistant (to pump the brake pedal).

Vehicle Preparation and Support

1. Loosen the wheel nuts Road and place the entire vehicle on jackstands. Make sure the car with the strong support before going ahead with this procedure!
2. Remove all road wheels.
3. Install one lug nut backward at each corner and tighten the nut against the rotor surface. Note that this step is to limit caliper flex that may distort pedal feel.
4. Open the hood and check the level of the brake fluid reservoir. Add the liquid required to ensure that the level is in the MAX deposit. Do not let the tank is empty at any time during the bleeding process!

The bleeding procedure

1. Start at the farthest corner of the driver and proceed in order toward the driver. (Right back, back left, front right, front left.) While the actual sequence is not critical to the performance of blood is easy to remember the sequence as the most distant from the nearest. This will also allow the system is bleeding, so as to minimize the amount of potential cross-contamination between the fluid new old.
2. Locate the bleeder screw at the rear of the caliper body (or drum brake cylinder of the wheel.) Remove the rubber cap bleed screw – and do not miss it!
3. Place-end wrench on the bleed screw. An offset wrench works best – because it allows a greater range of motion.
4. Place one end of clear plastic hose on the bleed screw nipple.
5. Place the other end of the hose into the disposable bottle.
6. Place the bottle for waste fluid on top of the caliper body or drum. Hold the bottle with one hand and grab the key with your other hand.
7. Instruct assistant to "apply." The assistant should pump the brake pedal three times, hold the pedal firmly, and respond with "applied." Instruct the wizard not to release the brakes until told to do so.
8. Loosen the bleed screw, with a brief ¼ turn to release fluid into the waste line. Screw only needs to be open to a second or less. (The brake pedal go down to the floor as the bleeder screw is opened. Instruct participants in advance not to release the brakes until instructed to do so.)
9. Close the bleed screw, pressing gently. Note that you do not have to pull the wrench with ridiculous strength. As Generally, only a quick jerk will do.
10. Instruct the assistant to "release" the brakes. Note: Do not release the brake pedal, while the bleed screw is open, as it will suck air back into the system!
11. The assistant should respond with "released."
12. Inspect the fluid within the drain pipe of the air bubbles.
13. Continue the bleeding process (steps 11 through 16) until air bubbles are no longer present. Be sure to check the brake fluid level in the reservoir after bleeding each wheel! Add the liquid needed to maintain the level in the mark MAX. (Typically, this process is repeated 5-10 times the wheel to make a 'standard' bleed.)
14. Move systematically towards the driver – Right rear, left rear, right front, left front – repeating the bleeding process at each corner. Be sure to keep a watchful eye on the brake reservoir liquid! Keep full!
15. When all four corners have been bled, spray the bleeder screw (and any other party which is moistened with spilled or leaked fluid brake) with brake cleaner and dry with a clean cloth. (Leaving the area clean and dry, it will be easier to spot leaks through visual inspection later!) Try to avoid spraying the brake cleaner directly on the pieces of rubber or plastic, as the cleaner can make these parts brittle after repeated exposure.
16. Test the brake pedal for a firm feel. (Bleeding the brakes will not necessarily cure a "soft" or "soft" pedal – since pad taper and compliance elsewhere in the system can contribute to a soft pedal. However, the pedal should not be worse than it was before the bleeding procedure!)
17. Be sure to inspect the bleeder screws and other fittings for signs of leakage. Correct as necessary.
18. Discard the liquid waste used as you would dispose of used motor oil. Important: used brake fluid should NEVER be poured back into the master cylinder reservoir!

Wrap-up of vehicles and road

1. Reinstall the four road wheels.
2. Lift all the vehicle and remove jackstands. Tighten the wheel nuts limit recommended by the manufacturer. Re-install any hubcaps or wheel covers.
3. With vehicle on a flat surface with the car does not work, and release the brake pedal several times until all permits, is included in the system. During this time, brake pedal feel may improve slightly, but the brake pedal must be at least as strong as it was before the bleeding process.
4. road test vehicle to confirm proper functioning of the brakes. BEWARE OF THE FIRST AMENDMENT TO DRIVE your car later to ensure the proper function of all systems vehicle!

How often do I need to bleed my brakes?

In closing, here are some golden rules to help determine the range of bleeding suitable for application in particular:

1. Under normal conditions operation, and without brake system modifications, typical of OEM brake systems are designed to require no bleeding during the life of the vehicle unless that the system is open to the repair or replacement. If you're driving around town or on the road to work, there's really no need to bleed! There are few vehicles European recommended replacement in a semi-regular basis for other reasons, however, so be sure to check the owners manual or service center for your particular application.
2. Those who choose to autocross or driving in a sport so you can choose to upgrade your brake fluid and bleed once year – this is a "good start to the season" maintenance item for low-speed competitors.
3. If your car see large amounts of high braking speed, or if you decide to participate in driver schools and / or lapping sessions, bleeding before each event is a good decision. More intense drivers at these events can choose the right beyond this step and at # 4 …
4. Finally, dedicated race cars should be bled after each track session.

About the Author

Redline Motive is your premier source for brake rotors http://www.redlinemotive.com/replacement/brakedisc.asp and brake pads http://www.redlinemotive.com/replacement/brakepadset.asp

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