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Brake Problem Help Me

Discussion in 'Mechanic and Repair' started by flattoplawncare, Mar 14, 2008.

  1. flattoplawncare

    flattoplawncare LawnSite Senior Member
    Posts: 321

    Hey guys i am usually pretty good at diagnoses, First i have a 99 chevy tahoe and the rear brakes went out (drum brakes) and the brake pedal traveled to the floor. So i put new shoes and both wheel cylinders in bleed the brakes and still same thing pedal still went to the floor but after i let the pedal back up the brakes would seem fine untill next time i stopped same thing to the floor. So then i replaced the master cylinder, i bench bleed it and installed it and then bleed the system. Now the pedal goes down 3/4 of the way and is still not really any better than before. When i hit the brake there is not much pressure but once again when it comes back up and i push it down again it feels normal. I dont know what else to try maybe the power booster? i don't know Please help me out.
  2. Two Seasons

    Two Seasons LawnSite Senior Member
    Posts: 791

    Sounds like you're bleeding brake fluid out a line or bleeder. Or you don't have a sealed system and are pulling air into it.

    Are you losing brake fluid?
  3. flattoplawncare

    flattoplawncare LawnSite Senior Member
    Posts: 321

    Nope not losing any fluid anywhere. when i push down on the pedal i hear air though?
  4. Two Seasons

    Two Seasons LawnSite Senior Member
    Posts: 791

    There is air trapped somewhere in there.

    You need to find the longest run of brake line from the master cylinder and open up the bleeder and let it run into a clean pan. Don't let the reservoir become empty as you'll start to suck air back into the system.

    Keep opening the longest line bleeder (after you refill the reservoir) until you cannot see anymore air bubbles. Then go to the second longest line and repeat. Do this until all lines are bled.

    Or you can go to an auto store tomorrow and get a bleeder buddy from them.
  5. flattoplawncare

    flattoplawncare LawnSite Senior Member
    Posts: 321

    Ok so 2 man one pumping brakes and then holding while the other cracks it open doesn't work? So should i crack open both bleeders in the rear and pour fluid into the reservoir. or should i do them one at a time? also should i not pump the brakes?
  6. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    I myself use a system with fish-tank air lines that I cut to a length and attach each to a valve then drop it into a cup that's partially filled with fluid and bleed them myself. But the liquid in the cup the hose dips down in it so when I let go of the pedal NO air gets sucked back in. Actually I don't even push the pedal, I just do what's called a 'gravity bleed,' only had to do this once so far and it worked but sometimes air bubbles can get stuck to the sides of the line so that's why the 'pressure bleed' is better.

    Those are the two kinds of brake bleedings, gravity and pressure.

    I think you might be doing it wrong, here's how the 2-man system works:
    One man HOLDS the brake.
    The other loosens the valve just enough to let it squirt.
    The first man still HOLDS the brake as it travels to the floor and KEEPS IT THERE!
    The other guy tightens the valve back up.
    Then, when the other guy says "AWWWRITE" that means the valve is shut, NOW the first guy lets go of the brake pedal to let it up.
    Repeat several times, for each wheel.

    Any other way, if you let Up on that brake pedal any time that valve is open you're just sucking air right back into the system.

    Another good method is get a hand-operated vacuum pump specifically made for this, Harbor Freight sells them.
  7. flattoplawncare

    flattoplawncare LawnSite Senior Member
    Posts: 321

    Yes that is how we did it i have never had any problems before bleeding brakes but i think i am going to do the gravity bleed. what if that doesnt solve my problem?
  8. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    You might, while gravity bleeding, right when the fluid is good on both the reservoir and the cup end, push that brake pedal one time to the floor good and let go. That should loosen any 'stuck' air bubbles.

    They do sell kits for it also, but after I bought one I ended up building my own.
    Plastic cups and fish-tank air line (transparency is key, the cups, too, so you can SEE if bubbles).
    3/16" and plenty of it, I'd get 10-12 feet if you have some left over it's better than not enough.
    Especially for a truck, it has to drop almost to ground level, a few feet is all right for one wheel at a time...

    Here's a neat article with pictures on just such a DIY kit:
    (that's even better than mine lol).

    Odd I never thought of pushing fluid UP the lines by raising that end, nifty concept.
  9. flattoplawncare

    flattoplawncare LawnSite Senior Member
    Posts: 321

    Ok my friend did the drums for me what if the auto adjuster is not working that could cause this problem to, or the drums could be to thin maybe? because my brakes worked fine before they started grinding in the rear. I should be able to set the parking brake and pump and if they go normal then it would be the self adjusters then right? he did kinda sit there blank for awhile when he did the drums.
  10. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Posts: 1,164

    Your brake booster is bad.

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