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Spongy and Airy Brake Pedal - Brakes Giving Out - Master Cylinder?

Discussion in 'Under the Hood' started by MistahYebba, April 24, 2017.

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  1. MistahYebba

    MistahYebba Active Member

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    Hi friends!

    When I press the brake pedal, it makes a 'whoosh' air sound like bellows. It goes down quite a ways before it starts applying decent braking.

    When at a stop (red light, for instance), the truck will want to creep forward and I have to press the brake pedal even harder.

    Occasionally, as you push the brake pedal down harder and all the way down in order to apply more braking force to stop creeping forward, the brakes stop working completely and the car is just free to roll forward...

    If you re-pump the brakes, they start 'operating' again.

    Master cylinder???

    I've already done rotors, calipers, pads.

    Also have a very small brake fluid leak. Doesn't appear to be at MC or any calipers.

    ABS light has been on for 2 years. Never used ABS. Related?

    Thanks for your time and help! :)
     
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  3. yostyexplorer94

    yostyexplorer94 1st Gen Mod Staff Member Moderator Elite Explorer

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    Sounds like you have air in your brake lines. Fix the brake leak first and bleed the brakes. Then see if that cures the problem.
     
  4. MistahYebba

    MistahYebba Active Member

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    Hello Yosty!

    Well; I'm just not sure.

    I bled the brakes starting from valve furthest from MC this morning.. no difference in breaking power.

    The method of bleeding was a tube on the bleeder valve leading to a bottle filled with some brake fluid.

    Partner pumps brakes and then holds firmly.
    I crack open bleeder valve and let any air/fluid run through. Pedal hits floor. Continue holding firmly.

    Close bleeder valve tightly and then okay to release pedal and repeat.

    Did this at each wheel and successfully got a straight stream of fluid with no air.

    As stated previously, bleeding with this method changed nothing.

    Still get a loud and weird "whoosh" sound as the very pedal VERY EASILY pushes all the way down (in park with engine ON).

    When driving, pedal goes down very easily with little effort... accompanied by the whoosh sound as you push down. But brakes do not apply until you are very far pushed down, almost towards the end.

    Please note that with engine off, pedal is very firm and I get no "whoosh" sound.



    As a test I removed vacuum hose from brake booster to remove power assistance from brake pedal. This made the truck run choppy and want to stall.

    Anyway, the pedal was obviously much firmer to push down, but still, brakes did not start to apply until the pedal was pushed down maybe 50% of the way. If I was going even 10MPH I would have to press the brakes very strongly and still maybe not stop in time.

    To me it sounds like booster is doing its job.. making the pedal easy to press??

    Please note I replaced master cylinder today in hopes it was a bad MC but did not help at all.

    I did not bench bleed the MC but I did that whole bleeding process again starting at rear wheel and repeated bleed pattern about 8 times per wheel. I also bled right at the MC brake lines. Seemed to be okay with no air... but still very spongy pedal that requires very little effort to press and makes an air sound as it goes down and also does not apply braking power until it's far down almost to the bottom.

    On a positive note, I can floor the brakes and come to a complete and firm stop. Hopefully it will stay that way.

    Most people say if the booster was bad the pedal would be hard to push. Not very very easy to push.

    I am wondering a few things;

    1. Is the booster making the pedal TOO easy to press down?
    2. Is the booster the cause of the air "whoosh" sound, almost like someone blowing up a balloon is I continue to push the pedal down? Or could it be something else causing the sound?
    3. If I still have air in the system, why is my bleeding procedure not working?
    4. Why does the pedal go so far down before the brakes start to apply, whether the booster has the vacuum hose attached or doesn't....?

    Thanks for your time and help!!!!
     
  5. MistahYebba

    MistahYebba Active Member

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    At this point I am thinking only a few things:

    1. Lots of air in the system which is somehow not getting out when I try to bleed with my method.
    a. Is there a better, more reliable bleed method? Should I crack the line(s) BEFORE the partner pumps the brakes, or after they have pumped and are holding?

    2. Brake fluid leak somewhere that I can't find causing air to get in which relates to #1.
    a. Could it possibly be within the rear brake components? I've never even looked at the rear brakes with my own eyes nor do I know how drum brakes work, but I am reading up on that now.
    b. Could it have anything to do with ABS system leaking, if it is? I don't even use ABS. The light has been on for the 2 years I've owned it. Doesn't that mean it's disabled anyway?

    c. Doesn't explain the "whoosh" sound when I press the pedal...

    3. Glazed brake pads and rotors? Is this a possibility? I got new pads just to get it out of the way, but when I looked at the old pads, they still had almost the same amount of meat on them... BUT, I wasn't checking for glazing.
    a. I can imagine this causing weak brakes due to lack of friction, but NOT the "whoosh" sound...

    4. Brake Booster might have something to do with the "whoosh" sound but I have absolutely no idea. Seems to do its job by making it very easy to press the pedal. Maybe too easy.


    MOST IMPORTANTLY, we all should remember that at a complete stop at a red light, the only thing you're "braking" is the idle drive speed... yet, the truck has recently been "creeping" forward until I apply more pressure to the pedal.

    The other day, upon applying more pressure, eventually the pedal was as far as it goes and there was no braking pressure at all, forcing me to put it in park and pump the brakes to get stopping power back.

    This screams MC to me, but since it has now been replaced, makes me wonder if it will ever happen again? Can anything else even cause that besides the MC--The pedal to be all the way pushed down, but still have no brakes?
     
    Last edited: April 25, 2017
  6. yostyexplorer94

    yostyexplorer94 1st Gen Mod Staff Member Moderator Elite Explorer

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    When you pump the brake pedal with the engine off you said it gets firm. Does it get to the point when you are pumping where you can hardly move the pedal with your foot? If it does and it doesn't leak down on you at all with pressure on the pedal then there should not be air in the system. This is with the engine still off.
     
  7. MistahYebba

    MistahYebba Active Member

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    Hi again Yosty!
    I just went out there and pumped the pedal with the engine off. The first pump is always very soft just like however it was when the engine was last on.. But after 3-4 pumps it becomes as "firm" as it's going to become (with the engine off)... I would definitely not say it ever gets to the point where I can "hardly move the pedal with my foot". It is a decently firm pedal but I can still push it down to the floor no matter how long I pump it.

    I actually feel as though the way the pedal feels when the engine is off after I've pumped it a few times, is how it SHOULD feel when the engine is ON!


    Does the sound that the pedal makes when the engine is on spark your interest at all?
     
  8. MistahYebba

    MistahYebba Active Member

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    Here is a video of the brake pedal air sound with engine running.

     
  9. MistahYebba

    MistahYebba Active Member

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    Anyone out there? :)
     
  10. nathan mayden

    nathan mayden Member

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    Sounds like air in the brake system and the woosh could be from the bellow on the brake shaft or maybe a problem with the booster all that air has to go somewhere.
     
  11. MistahYebba

    MistahYebba Active Member

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    How could there still be air when I've bled the brakes?
     
  12. nathan mayden

    nathan mayden Member

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    Not bench bleeding the mc was probably a mistake these can take a long time to bleed. If pedal travel is still excessive I would take a look at your rear brake components. They are supposed to be self adjusting but rarely properly.
     






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