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Losing brake pedal pressure...again

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 88K5Jimmy, Aug 18, 2003.

  1. 88K5Jimmy

    88K5Jimmy 1/2 ton status

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    After installing the lift, extended brake lines, new front calipers, brake hardware and bleeding the entire system twice, I am still losing brake pedal pressure. The pedal feels excellent after we re-bled the rear lines because thats where we thought we had air in the system. I could lock up the brakes and the pedal was great. After a couple of days the pedal starts to fade and then its like there is no pedal and the brake light comes on. I am thinking about replacing the master cylinder and re-bleeding the entire system and see what that does.

    Anybody have any other suggestions? Ohh, it is the stock disk/drum setup.

    Thanks
    Ross
     
  2. NITRO

    NITRO 1/2 ton status

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    its your MC.....replace that and u will b good to go

    NITRO
     
  3. slider

    slider 1/2 ton status

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    Look where your mastercylinder bolts to the booster, is there any paint left? is it weaping fluid? Pull the mastercylinder off the booster and look in the booster for fluid. When you pump the brakes does the pedel get better on the second or third stroke? It sounds like you still have air in the system but mastercylinders are cheap. Bench bleed the cylinder until it recurclates fluid with no bubbles, then bolt it on. Open all the beeders and let it gravity bleed for a while then do a normal bleed. Sometimes if you let a buch of air into the system it takes some time to get all of it out. I have had to tap on the wheel clyinders and calipers with a rubber mallet to get on system to bleed. bleed it rr lr rf lf .good luck
     
  4. 84_Chevy_K10

    84_Chevy_K10 Banned

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    How's the rear brakes? Are either sides of the master going dry?
     
  5. 88K5Jimmy

    88K5Jimmy 1/2 ton status

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    No, the master cylinder isn't going dry. We thought our problem was in the rear brakes so that's why we only bleed them. However that isn't the case, I'm assuming, because I've lost pedal pressure for the second time.
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    When my MC was on its way out, and I'd lose pedal pressure, 2 or 3 pumps and I would regain most of the pedal.

    Typically pedal wuld just start dropping (such as at a light) and then the brake light would come on, and I'd start rolling. Should have been a clue when I rebuilt it and could never get the "sponginess" completely out of the brake system. Pedal never was firm like it should have been.

    Spent a lot of time bleeding my system, but as is so often the case, if you bleed your brakes with an old MC, it typically will fail.
     
  7. Rolled

    Rolled 1/2 ton status

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    Rear cylinders leaking? Just a thought...
     
  8. 88K5Jimmy

    88K5Jimmy 1/2 ton status

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    Rear cylinders aren't leaking, put them on a while ago and just reused them on my swapped in axle.

    I'm not losing pedal pressure when at a stop, but I can press the pedal down and make the light come on.
     
  9. TrcksR4ME

    TrcksR4ME 1/2 ton status

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    You sure the rear wheel cylinders aren't leaking, as in you took the drums off and checked? Might be newer cylinders, but that doesn't mean one isn't going out. Everyone jumps to MC as the first thing, which is what I did, and it wasn't the problem. Also on my wheel cylinder problems there was not enough of a leak to see or smell it for quite some time, but my symptoms were very similar, would bleed it, would be good, and slowly start to fade, with the brake light coming on.
     
  10. slider

    slider 1/2 ton status

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    Your combination valve is toast or you still have air in the system. My buddy had the same exact problem we could not get the light to stay off, we re-bled the system including the combination valve and it still would not go off. Replaced the valve and no more problem. /forums/images/graemlins/thumb.gif
     

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