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How to Bleed Brakes - The RIGHT Way

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  • How to Bleed Brakes - The RIGHT Way

    [html:2pp5pd7r]<p align="center"><font size="6"><b>How to Bleed Brakes – The <i>Right </i>Way</b></font></p>

    <p class="copyHeading"><b>Brake System Basics</b></p>

    <p class="copy">The workings of the brake system may, at first glance, seem
    obvious: we push on the brake pedal, which clamps the pads onto
    the rotor, which stops the car, right? But think further: a
    2400-pound vehicle in motion possesses a great amount of kinetic
    energy &#40;the energy of motion.&#41; And the laws of physics dictate
    that energy cannot be created or destroyed. So what happens to
    all of the kinetic energy from a moving vehicle when the vehicle

    <p class="copy">Since the energy cannot be destroyed, then it must be
    converted into something else. In this case, it is converted into
    heat. And it is this conversion process that is the true function
    of the braking system. <i>Brakes convert kinetic energy into heat
    energy through friction</i>. And once all of a vehicle’s
    kinetic energy has been converted, the vehicle stops – since
    it has no more kinetic energy – and ends up with lots of
    heat energy. This heat energy is created as a result of friction
    between the brake pad and the rotor &#40;or the shoe and the drum,&#41;
    briefly stored in the rotor &#40;or drum,&#41; and eventually dissipates
    into the surrounding air. </p>

    <p class="copy">But how does the input of force at the brake pedal &#40;from our
    foot&#41; result in clamping force – and hence friction -
    between the brake pads and the rotor? Like most of the functions
    of a modern car, the operation of the &quot;brakes&quot; is
    actually part of a larger integrated &quot;system.&quot; And
    while there are many important parts of the braking system,
    suffice it to say that brake fluid is a <i>very</i> vital
    component within the system. </p>

    <p class="copy">In a nutshell, when we apply force to the brake pedal with our
    leg, this force is increased &#40;thanks to the lever law&#41; based upon
    the length of the brake pedal lever. This force moves through the
    vacuum booster – where it gets amplified by the motor’s
    vacuum – and finally gets transferred into the piston within
    the master cylinder. The force against the piston in the master
    cylinder pushes the piston into brake fluid. The fluid is then
    forced through the brake pipes toward the brake components at the
    corners of the car. Finally, the fluid pushes against the piston
    within the brake caliper - which clamps the brake pads against
    the rotor.</p>

    <p class="copy">Clearly, the fluid is vital – since we depend upon the
    liquid properties of the fluid to transfer force through the
    system into the brakes at the wheels. In theory, since a liquid
    cannot be compressed, we can count on the hydraulic actuation to
    result in a linear transfer of forces. &#40;In other words, we do not
    expect liquid to compress. If it did compress, then we would
    &quot;waste&quot; energy compressing the fluid instead of using
    the energy to create movement at the brake corners.&#41;</p>

    <p class="copy">In summary, the role of the brake fluid within the braking
    system is to transfer the force from the master cylinder to the
    corners of the car. And a vital characteristic of brake fluid
    that allows it to perform its task properly is its ability to
    maintain a liquid state and resist compression.</p>

    <p class="copyHeading"><b>Why Bleed the Brakes?</b></p>

    <p class="copy">The term &quot;bleeding the brakes&quot; refers to the process
    in which a small valve is opened at the caliper &#40;or drum&#41; to
    allow controlled amounts of brake fluid to escape the system.
    &#40;When you think about it, &quot;bleeding&quot; may appear to be a
    somewhat graphic term, but it aptly describes the release a vital

    <table border="0" cellpadding="4">
    <td><font color="#FF0000" size="2">*Note: technically,
    &quot;air&quot; only enters the lines if there is a
    compromise of the system’s sealing &#40;as when flex
    lines are removed or replaced.&#41; When fluid boils, it will
    instead create &quot;fluid vapor.&quot; Vapor will create
    an equivalent efficiency loss. But we use the term
    &quot;air&quot; here for simplicity.</font></td>
    <td>We bleed the brakes to release air<font color="#FF0000">*</font> that sometimes becomes trapped
    within the lines. When air becomes present within the
    lines, it creates inefficiencies within the system
    because, unlike liquid, air can be compressed. So when
    enough air fills the lines, input at the pedal merely
    causes the air to compress instead of creating movement
    at the brake corners. In other words, when air is present
    within the system, the efficiency and effectiveness of
    the braking system is reduced. Usually, a small amount of
    air within the brake system will contribute to a
    &quot;mushy&quot; or &quot;soft&quot; pedal &#40;since less
    energy is required to compress the air than is required
    to move fluid throughout the brake lines.&#41; If enough air
    enters the brake system, it can result in complete brake

    <p class="copy">So how does air enter the lines in the first place? Sometimes,
    it can be the result of a service procedure or an upgrade –
    such as replacing the stock flex lines with stainless steel
    braided lines. But often it is the result of high temperatures
    that cause brake fluid components<font color="#FF0000"> </font>to
    boil, thus releasing gasses from the boiling fluid into the brake

    <p class="copyHeading">Brake Fluid Selection</p>

    <p class="copy">This leads one to contemplate the type of liquid that is used
    as brake fluid. In theory, even simple water would work –
    since, being a liquid, water cannot 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, testing on the scR showroom stock racecar
    has shown that rotor temperatures during a race will become as
    high as 1100 degrees Fahrenheit.<font color="#FF0000">*</font>
    Since the boiling point of water is 212 degrees Fahrenheit, it is
    easy to see that water within the brake system could boil easily
    – and therefore release gases into the brake pipes –
    which will reduce the efficiency of the system. &#40;Water would also
    present a big problem in cold weather if it froze to ice!&#41;</p>

    <table border="0" cellpadding="4">
    <td>The &quot;obvious&quot; solution to this problem is
    to utilize a fluid that is less sensitive to temperature
    extremes. Hence the development of &quot;brake
    fluid.&quot; However, there unfortunately is no such
    thing as a &quot;perfect&quot; brake fluid. And like most
    things in the world, the addition of certain beneficial
    characteristics usually brings tradeoffs in other areas.
    In the case of brake fluid, we generally must balance the
    fluid’s sensitivity to temperature against its cost
    and its impact upon other components within the system.</td>
    <td><font color="#FF0000" size="2">*Note: Even though the
    rotor gets very hot, the brake fluid will never see such
    high temperatures – since the heat must be passed
    through the brake pad, caliper, piston, and other
    components. Most of the heat will dissipate along this
    route before reaching the brake fluid. Previous testing
    has indicated that a rotor temp between 800-900 degrees
    Fahrenheit can result in a fluid temperature closer to
    300 degrees Fahrenheit – still enough to boil water!</font></td>

    <p class="copy">Stated more bluntly, it is possible to reduce a fluid’s
    sensitivity to temperature by varying 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.</p>

    <p class="copy">The chemical composition and minimum performance requirements of the fluid are generally
    indicated through a rating such as &quotOT3,&quot; DOT4,&quot;
    or &quotOT5.&quot; The DOT-rating itself is assigned after a
    series of government tests. However, this rating is NOT intended
    to indicate boiling points, even though higher DOT ratings
    generally do correspond with higher boiling points. Perhaps more
    importantly, the DOT rating <i>does</i> indicate the base
    compound of the brake fluid - which allows manufacturers to
    specify fluid types which are less likely to react negatively to
    known materials used within a particular braking system.</p>

    <p class="copy">The greatest irony about brake fluid, however, is the fact
    that the chemical compositions that tend to be less sensitive to
    temperature extremes also tend to attract and absorb water! So
    even though the fluid <i>itself </i>is unlikely to boil &#40;most
    glycol-based DOT3 fluids have a &quot;dry boiling point&quot;
    around 400 degrees Fahrenheit,&#41; the water that it absorbs over
    time tends to boil easily &#40;at 212 degrees Fahrenheit.&#41; It is this
    characteristic of absorbing moisture that leads to the measure
    known as the &quot;wet boiling point.&quot; The wet boiling point
    is the equilibrium boiling point of the fluid after it has
    absorbed moisture under specified conditions. Because brake fluid
    will absorb moisture through the brake system’s hoses and
    reservoir, evaluation of the wet boiling point is employed to
    test the performance of <i>used</i> brake fluid and the
    degradation in it’s performance. &#40;And it is why we still
    need to bleed the brakes frequently on the racecars, even though
    we use AP600 racing fluid that costs $18 per bottle!&#41; The lesson:
    do NOT expect to avoid bleeding your brakes just because you
    bought expensive brake fluid.</p>

    <p class="copy">As one might guess, &quot;racing&quot; fluids will use
    relatively &quot;aggressive&quot; chemical compositions which
    will tend to have higher wet boiling points and higher costs,
    while the average street fluids will use more conservative compositions which will have lower wet
    boiling points and lower costs. In some cases – such as a
    purpose-built racecar – the tradeoffs of using the expensive
    racing fluid is outweighed by the competitive advantages. But for
    the average driver – whose driving style is less likely to
    induce very high brake temps – the costs of the fluids and
    potential wear-and-tear factors upon system components may
    justify the use of a more conservative fluid with a lower wet
    boiling point.</p>

    <p class="copyHeading">The Proper Bleeding Procedure</p>

    <p class="copy"><b>Supplies Preparation</b></p>

    <p class="copy">You will need the following tools:</p>

    <li>10mm box-end wrench &#40;8mm for rear drum brake units.&#41; An
    offset head design works best.</li>
    <li>Extra brake fluid<font color="#FF0000"> </font>&#40;1 pint if
    you are just bleeding, 3 if you are completely
    <li>14-inch long section of 3/16 in. ID clear plastic tubing.</li>
    <li>Disposable bottle for waste fluid.</li>
    <li>One can of brake cleaner.</li>
    <li>One assistant &#40;to pump the brake pedal.&#41;</li>

    <p><b>Vehicle Preparation and Support</b></p>

    <li>Loosen the lug nuts of the road wheels using a 19mm
    socket and place the entire vehicle on jackstands. Be
    sure that the car is firmly supported before going <b><i>ANY</i></b>
    further with this installation! </li>
    <li>Remove all road wheels.</li>
    <li>Install one lug nut backward at each corner and tighten
    the nut against the rotor surface &#40;to limit flex that may
    distort pedal feel.&#41;</li>
    <li>Open the hood and check the level of the brake fluid
    reservoir. Add fluid as necessary to ensure that the
    level is above the seam of the reservoir. Do not let the
    reservoir become empty during the bleeding process.</li>

    <p class="copy"><b>Bleeding Process</b></p>

    <li>Begin at the corner furthest from the driver and proceed
    in order toward the driver. &#40;Right rear, left rear, right
    front, left front.&#41;</li>
    <li>Locate the bleeder screw at the rear of the caliper body
    &#40;or drum brake wheel cylinder.&#41; Remove the rubber cap
    from the bleeder screw.</li>
    <li>Place the box-end wrench over the bleeder screw &#40;10mm for
    discs, 8mm for drums.&#41; An offset wrench works best –
    since it allows the most room for movement. &#40;If you do
    not have an offset wrench, avoid pushing the wrench head
    to the bottom of the bleeder screw – since the
    wrench may interfere with other parts during movement.
    Allow a standard wrench to sit near the top of the
    bleeder screw contact point.&#41;</li>
    <li>Place one end of the plastic hose over the nipple of the
    bleeder screw.</li>
    <li>Place the other end of the hose into the disposable
    <li>Place the bottle for waste fluid on top of the caliper
    body or drum unit. Hold the bottle with one hand and
    grasp the wrench with the other hand.</li>
    <li>Instruct the assistant to &quot;apply.&quot; The
    assistant should pump the brake pedal three times, hold
    the pedal down firmly, and respond with
    &quot;applied.&quot; Instruct the assistant not to
    release the brakes until told to do so.</li>
    <li>Loosen the bleeder screw with a brief &frac14; turn to release
    fluid into the waste line. The screw only needs to be
    open for one second or less. &#40;The brake pedal will
    &quot;fall&quot; to the floor as the bleeder screw is
    opened. Instruct the assistant in advance not to release
    the brakes until instructed to do so.&#41; </li>
    <li>Close the bleeder screw. </li>
    <li>Instruct the assistant to &quot;release&quot; the brakes.
    Note: do NOT release the brake pedal while the bleeder
    screw is open, as this will suck air into the system! </li>
    <li>The assistant should respond with &quot;released.&quot;</li>
    <li>Inspect the fluid within the waste line for air bubbles.</li>
    <li>Continue the bleeding process &#40;steps 11 through 16&#41; until
    air bubbles are no longer present. Be sure to check the
    brake fluid level in the reservoir after bleeding each
    wheel! Add fluid as necessary to keep the level above the
    seam line.</li>
    <li>Move systematically toward the driver – right rear,
    left rear, right front, left front - repeating the
    bleeding process at each corner. </li>
    <li>When all four corners have been bled, spray the bleeder
    screw &#40;and any other parts that were moistened with
    spilled or dripped brake fluid&#41; with brake cleaner and
    wipe dry with a clean rag. &#40;Leaving the area clean and
    dry will make it easier to spot leaks through visual
    inspection later!&#41; Try to avoid spraying the brake
    cleaner DIRECTLY on any parts made of rubber or plastic,
    as the cleaner can make these parts brittle after
    repeated exposure. </li>
    <li>Test the brake pedal for a firm feel. &#40;Bleeding the
    brakes will not necessarily cure a &quot;soft&quot; or
    &quot;mushy&quot; pedal – since pad taper and
    compliance elsewhere within the system can contribute to
    a soft pedal. But the pedal should not be any worse than
    it was prior to the bleeding procedure!&#41;</li>
    <li>Be sure to inspect the bleeder screws and other fittings
    for signs of leakage. Correct as necessary.</li>
    <li>Properly dispose of the used waste fluid as you would
    dispose of used motor oil. <font color="#FF0000">Important:
    used brake fluid should NEVER be poured back into the
    master cylinder reservoir! </font></li>

    <p><b>Vehicle Wrap-Up and Road Test</b></p>

    <li>Re-install all four road wheels. </li>
    <li>Raise the entire vehicle and remove jackstands. Torque
    the lug nuts to 140 Nm &#40;103 ft-lb&#41; using a 19mm socket.
    Re-install any hubcaps or wheel covers also using a 19mm
    <li>With the vehicle on level ground and with the car NOT
    running, apply and release the brake pedal several times
    until all clearances are taken up in the system.</li>
    <li>Road test the vehicle to confirm proper function of the
    ALL VEHICLE SYSTEMS!</i></b></li>


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