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to brake or not to brake!!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by tipoil, Aug 19, 2002.

  1. tipoil

    tipoil 1/2 ton status

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    I have a 77 blazer whit power brake (rear drum,front disk)
    The problem is that i can't get any pressure buildup to the rear(the pedal goes to the floor)and wen i try to bleed the wheel cylinder i still get no pressure (can hold the pressure whit my finger,and whe i let go it just ooze out (no pressure!) that's whit my freind pushing on the pedal at the same time.
    Since i got no pressure at both wheel cylinder i tought that i had a bad line .So i removed the metal line that's comming from the front were it bolt to the rubber ones in the back ,Still no pressure (in the metal one!!)
    Next i removed the metal line at the combi.valve (the one that go to the rear)still no pressure at the valve!!
    then i remouved the line at the master and ... PRESSURE AT LAST!!!was not able to hold the pressure whit both my tumb and the pedal was harder to push(sure it was not like new but was better whit my tumb on it!!)

    So do i get a new master or a new metering valve or i'm way off!!!

    by the way i have no prob whit the front (got pressure and is bled (no more air in) )
    PLZ HELP MEEEEEEE!!!!!!!!
     
  2. YtseJam

    YtseJam 1/2 ton status

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    Sounds like the combination valve is junked. If you are going to replace the combination valve it's a good time to flush out all of the brake lines. Also a remanned master is pretty cheap too while you're at it.
     
  3. tipoil

    tipoil 1/2 ton status

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    Anyone else have a idee
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Master cylinder is my idea. Combo valves don't typically fail, (what, one moving critical piece?)but are always blamed.

    The combo valve "restricts" if you will, fluid flow, so you get that 60/40 front/rear bias that you want, and GM intended. So if the prop valve is working, it puts (as far as I can tell) "bakc" pressure on the master cylinder. If the cylinder seals leak, then the fluid will lose pressure as it goes back into the master cylinder. You might even be able to watch this if you pull the MC lid off, and have someone depress and hold the brake..if fluid level rises, you would have leaky MC seals.

    MC's usually fail when bled, if old, because crud builds up in the bore. When you bleed them after 10-20 years, the piston suddenly travels further than it ever has (when the pedal hits the floor) and goes right into the crud and corrosion, tearing the seals.

    I had that happen to me, and I could NEVER get rid of the spongy brakes. Drove it for awhile, it wasn't unsafe, just not right. Finally the pedal dropped at a light, and the brake light came on, and I figured it was time for a new MC< and sure enough, that solved the problem.

    I'd verify that your brake light warning circuit is working though, with the key on, ground the tan(? on my year anyway) wire at the combo valve, and the light should come on in the cab. If it does, then the warning light circuit is working. Then try the brakes again, if you are getting no fluid to the rears, then you *should* see that warning light come on, as the pressure will be incorrect, and the combo valve should see it.

    I believe you can clean the combo valve out pretty easily, it wouldn't hurt to do that at least, I just don't think its the problem. I've heard of one or two combo valves that have failed, but thats nowehere near the times I've seen them blamed.
     
  5. tipoil

    tipoil 1/2 ton status

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    U ARE MY HERO dyeager535

    u were correct !!!
    just finish putting in the new master in and guess what??
    it WORKS!!!!
    thank u dude u just save me 100 $$ (canadian)(the price of the combi.valve)
    hyyyyyyhaaaa!!!! /forums/images/icons/smile.gif /forums/images/icons/smile.gif /forums/images/icons/smile.gif /forums/images/icons/smile.gif /forums/images/icons/smile.gif /forums/images/icons/grin.gif /forums/images/icons/grin.gif /forums/images/icons/grin.gif /forums/images/icons/grin.gif /forums/images/icons/grin.gif /forums/images/icons/grin.gif /forums/images/icons/grin.gif
    thanks again!!!!!1
     

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