Question about 1999 Chevrolet Silverado 1500

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Brakes are still spongy after changing the pads, one caliper, and master cylinder. bled front brakes.

Changed the brake pads including one caliper and master cylinder. Brakes are still spongy and will go to the floor. Bled the front brakes.

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  • jeffery_lowe May 21, 2009

    HOw do I bleed the back drum brakes?

  • jeffery_lowe May 23, 2009

    I have bench bled the master cylinder and then bled all the brakes. The troubling part of this problem is that the brakes are nice and tight until I start the vehicle. Then the pedal goes to the floor. Could this be the power boost unit?

  • jeffery_lowe May 24, 2009

    The brakes do not get any higher when pumping them. They stay soft and go to the floor board. The back brakes have not been changed but I checked them and they have nearly full pad left. Changed left rear cylinder.

  • jeffery_lowe May 24, 2009

    Changed the master cylinder and also adjusted the back brakes. Could the power boost be causing this problem?

  • jeffery_lowe May 26, 2009

    Kept bleeding the right rear and found a small amount of air after about 2 cups of fluid. They are fine now. Thanks for your help.

  • Jeff Hammack
    Jeff Hammack May 11, 2010

    Check the master cylinder accuator rod, between the master cylinder and the brake booster, make sure it is adjusted correctly, you should be able to remove the master to check this without disconnecting the brake lines, if it is adjusted correctly reinstall then verify bleeding. If you are positive you have all of the air out and still your prdal drops to the floor, I would return that master cylinder and get a new one. With no external leak and air out of the system the only thing that can cause the pedal to drop is internal master cylinder leakage, let me know what you find

  • Jeff Hammack
    Jeff Hammack May 11, 2010

    do your brakes pump up? meaning if you pump the brakes while the engine is running will the pedal get firmer and higher from the floorboard? Have you replace rear brakes?

  • Jeff Hammack
    Jeff Hammack May 11, 2010

    did you bench bleed the master cylinder before installation? First bleed the master at the connection lines one at a time, then since you replaced the master you will need to bleed all wheels, starting at the right rear first, then left rear, then right front then left front, ensure the master cylinder stays full during all bleeding, and that you bleed out all air from each location, then test brake pedal for firmness, let me know what happens


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I just went to Brake Masters this morning and had them replace the Master Cylinder since I was experiencing the pedal very spongy and going to the floor. When they replaced the Master Cylinder and they gave me back the car, the brakes were still spongy and going to the floor. I addressed this to them and they took another look at it, but when I took it for a second time, the brakes were extremely spongy. It was almost like they gave me back my car in worst condition to when I brought it in. Can you help?

Posted on Jul 31, 2010

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You have air in the system. You need to bleed the brakes. Start at the right rear tire and then the left rear, then right front, the left front. Keep an eye on the res. don't let it run out of fluid. Pump the peddle and bleed in order outlined above. (don't release the peddle untill the bleeder is tight.)

Posted on May 21, 2009

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  • Bennie Kennedy May 22, 2009

    Look behind the drum.(stick your head in the finder well) At the top of the drum(on the back side) There is a bleeder.

  • Bennie Kennedy May 24, 2009

    If the brakes have all the air out, the pedel should stay at the top like normal. If the pedel starts out good and slowly goes to the floor, you may have gotton a bad mastercylender. It does happen. Sometimes air is harder than you think to get out, espically after doing as much work as you did. Try one more time bleeding them. Pump the pedel 'till it's hard then crack the bleeder. (don't let off the pedel after it goes to the floor. Make sure the bleeder is tightend up first) Syart at the rear wheels then the front. watch the master cylender :don't let it run out of fluid. If it still has a bad pedel, adjust the rear brakes. (spin the drum while you turn the adjuster.) If all else fails, try another mastercylender.

  • Bennie Kennedy May 25, 2009

    the booster only helps work the brakes, it has nothing to do with the hydrloic part of the system. It's got to be air. Check the connections (clean with brake cleaner). See if you can find a pressure bleeder. ( rent one??).

  • Bennie Kennedy May 26, 2009

    thank god, I thought I was loosing my mind!!

  • Rae Nap Nov 10, 2013

    It was my understanding the the vacuum booster is where the air gets sucked out before entering the brake lines. If booster is not working properly would this not cause air to enter the brake lines giving it it's spongy feel?


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Glad you got it going, hope info was helpful, have a great day!

Posted on May 26, 2009

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