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prop valve

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by BobK, Mar 19, 2001.

  1. BobK

    BobK 1/2 ton status

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    Saw this on the 73+up forum and got me thinkin.The brass pin on the prop. valve...do you push it in or pull it out when bleeding the brakes on the 69-72 Blazers.
    Thanks,Bob.

    [​IMG]<font color=green>BobK<font color=green>
     
  2. Triaged

    Triaged 1/2 ton status

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    I think you push it in (at least that is how I did it and it seams to work).

    '71 Blazer CST with alot of rust
     
  3. arq

    arq 1/2 ton status

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    push it in...

    ARQ.
     
  4. Steve_Chin

    Steve_Chin 1/2 ton status

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    I agree with the above two posts. In fact, the Factory Service Manual says to use a special tool or make a special tool to hold the plunger into the body of the combination valve while bleeding.
     
  5. R72K5

    R72K5 Banned

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    Ok, heres a dumb question,, Ive removed and installed many of these proportioning valves, yet dont really know what pressing the pin actually accomplishes, other than maybe holing the piston, inside, in a certain position ??

    Oh, and while Im here, howcome my 72 wouldnt have a prop valve plumbed, or even one that exists,
    and whats bad gonna happen if it was driven without one ??

    '72 K-5 4x4, CST, 3.07, 4 speed, NP 205, 31' x 10.5", Olive green and primer, rusted out, rice smasher!
     
  6. Steve_Chin

    Steve_Chin 1/2 ton status

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    Yup... It just holde the piston in a certain position. It helps to overcome the RPV and allow proper bleeding of the rear brakes.

    No combination valve in your '72??? Sheesh. That might cause your brakes to grab funny (front before the rears) or to lock one end up before the other during hard braking (probably the rears will lock early). Don't the lines have fittings for one below the master cylinder?
     
  7. arq

    arq 1/2 ton status

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    I have a 72 without one. I have been driving for about 3yrs without it(prev owner took it out). Any how, if i stop slowly no problem. when i do try and stop fast(slam the brakes) all bets are off as to what side it will pull. It is scarry if you have not been in that situation before. takes a bit to get used to it, or you can just fix it. I don't drive that beast much anymore, but the one i am driving has the prop valve and the difference is noticable.

    ARQ.
     
  8. BobK

    BobK 1/2 ton status

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    Well I tried the" push in" thing and it didn't do much.1st I could only push the pin in approx.1/32 of an inch(it hardly moved).I can pull it out approx.1/16 to 1/8 of an inch,it will then "spring" back in if not held out.I then bled the brakes with the pin pushed in.
    I just can't seem to get these brakes right!Like I said before,it seems the brake pedal bottoms out before enough pressure can be generated.WHAT THE HELL AM I DOING WRONG!

    [​IMG]<font color=green>BobK<font color=green>
     
  9. arq

    arq 1/2 ton status

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    bobk,

    how exactly are you bleeding the brakes. I had a hell of a time with mine. turn out to be the pads but through that proccess i found many mistakes. here are a few.

    1) when bleeding the brakes i noticed that i got are air along the threaded part of the bleed screw.

    2) Rear brake adjustment is critical. If it's not adjusted properly your front brake will never catch.

    3) carefull when you frist put on your master cylinder you could damage it when pushing the pedal all the way in. something about the seals bottoming out. i somehow tore up my first.

    4) don't pump to fast you could create bubbles.

    5) adjust the booster to master cylinder push rod properly.

    if you have questions on any of the above email me directly.

    ARQ.
     
  10. Triaged

    Triaged 1/2 ton status

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    Which are you having prob's with, front, rear, or both. I had prob's w/ the rear. I ended up having to bleed the line starting at the master. I bleed every joint on it before I could even get any fluid to the rear (no fluid in system...long story). If you try this use flare fitting wrenches or you will strip each one.

    '71 Blazer CST with alot of rust
     
  11. BobK

    BobK 1/2 ton status

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    Might have bottomed out the master cylinder when I 1st got it on.I bleed the system with a MityVac vacume pump now.I do get small bubbles when bleeding the rear brakes.I've heard if you put teflon tape on the bleeder nipple threads it'll help with those little bubbles.Arq,what happens if you bottom out the master cylinder?Is it repairable or is it toast?How can you tell if it was bottomed out.I'm pretty sure I adjusted the master cylinder push rod length properly.Thanks,Bob.

    [​IMG]<font color=green>BobK<font color=green>
     
  12. arq

    arq 1/2 ton status

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    Bobk,

    i am glad you caught the bubbles problem. I had the same problem so i took the bleeder screw out and riged an old brake line. I also used the vaccum method for priming the brake lines. then i had someone push the pedal slowly while i took it out and replaced it with the bleeder screw. while the pedal was down i went to the other side of the axel and hooked up my contraption, vaccumed the fluid, let the pedal go, vaccume again, then replace the bleeder screw like mentioned previously.

    as for bottoming out the MC, it will damage your seals. you will have to take it apart and replace them or take it back where you bought it and use up the warrantee(spelling). i am not sure if there is another method of checking to see if you toasted your MC.

    i have seen another method for bleeding the MC. They are just plugs for the brake lines, then you pump the MC till you get no more bubbles. I would assume that the pedal would begin to get harder to push down. If the seals are damaged the pedal would remain soft all the time. I am not sure on this one but someone else may.

    ARQ.

    PS: where did you get the animated flying canadian flag?? you think i can get an animated mexican flag.<P ID="edit"><FONT SIZE=-1>Edited by arq on 03/22/01 12:36 PM (server time).</FONT></P>
     
  13. BobK

    BobK 1/2 ton status

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    I did a search under "canadian flag gif" and just checked out the site that resulted in the search.Here's one for you
    <A target="_blank" HREF=http://www.animfactory.com/af_flags_poles_nations_gn_page_bf.html>http://www.animfactory.com/af_flags_poles_nations_gn_page_bf.html</A>
    found it by doing a search under " mexico flag gifs".

    [​IMG]<font color=green>BobK<font color=green>
     

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