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Brake Bleed Combination Valve

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BigBen, Jan 6, 2003.

  1. BigBen

    BigBen 1/2 ton status Premium Member

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    OK,

    I know from searching that I need to hold in the "pin" on the combination valve while I bleed the brakes. I was feeling around last night and I found the rubber cap over the pin.

    The question is:

    Is the pin "normally in" and I just need to hold it in.

    -or-

    Is the pin "normally out" and I need to push it in and then hold it in.

    I pushed on the end of the rubber cap last night and didn't really feel anything moving.

    /forums/images/graemlins/1zhelp.gif


    -Ben
     
  2. Triaged

    Triaged 1/2 ton status

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    It is normally in and you just need to hold it.
    I found that a stick of the right length propped up against the core support worked the best to hold it. I have seen one special tool used to hold it in but I have no idea where to get one.
     
  3. slider

    slider 1/2 ton status

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    Are you using a pressure bleeder or manual bleeding the brake system? The only time you need to hold open the pin in the combination valve is when you are pressure bleeding the brake system. if you are just doing a manual system bleed or are using a vacuum bleeder you do not need the combo valve held open. Pressure bleeding is kinda a thing of the past. We do not use them anymore along with most other shops I know of. Heres the best way I bleed the brakes. Remove most of the old fluid so your not putting all that contaminated stuff into your system. Fill the resivor full and gravity bleed the system for a while. Get your helper, close all the open bleeders and do a vacuum and then a manual bleed. If you do not have a vacuum bleeder the just manual bleed the whole system. If when you do not see any fluid flowing during the gravity bleed make sure the bleeder is not clogged with mud and crap. If you run low on fluid start over. Its that easy. R Rear L rear R front L front top then off the master cylinder /forums/images/graemlins/thumb.gif
     
  4. BigBen

    BigBen 1/2 ton status Premium Member

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    Triaged: Thanks, then what I noticed made sense.

    Slider: Thanks for your input. I plan to manually bleed the brakes. You can see here where some of my confusion comes from......

    I don't believe my Haynes manual mentions the Combo valve at all. My Chiltons says to hold it in, and the '74 shop manual says to hold it in specifically during manual bleeding. With every book being different, I wasn't sure what to do. /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif Thanks for letting me know it isn't necessary with manual bleeding.

    On top of that, everything I have ever heard says to go from furthest (R Rear) to nearest (L Front), but the '74 GM Light Truck Manual says just the OPPOSITE! I'm going to assume that after thirty years the 74 manual is probably not the best resource. /forums/images/graemlins/tongue.gif /forums/images/graemlins/crazy.gif

    Gravity bleeding the whole system sounds like a good idea. Especially since my master cylinder was off for a few months while I was changing the booster and engine.......

    Thanks,

    -Ben
     
  5. Alex

    Alex Registered Member

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    slider, sorry for the dumb question, but what is gravity bleeding? This is the first time I heard about this. Is it just opening the system up and letting all the fluid out without pumping the brakes? /forums/images/graemlins/confused.gif
     
  6. imiceman44

    imiceman44 1 ton status

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    Yep, that is the way I do it when I did more than one end or when I want to change the fluid, I drain it all, then fill with new fluid, give it a few pumps and let it fill slowly until I don't see much bubles getting out, I close all and start bleeding each end.
     
  7. Alex

    Alex Registered Member

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    imiceman44, do you open all the nipples or just one at a time starting from the farthest wheel from the master cylinder. Will the system drain completely even through the proportioning valve and wheel cylinders without pressure? Also you mentioned that you bleed the system afterwards. Why do that if the system was completely drained and replaced with new fluid (knowing that no air was captured in the lines)? Just trying to understand, thanks.
     
  8. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    You push in around the pin then grab the pin and pull out. There is actually a special tool for this. The pin cannot be pressed in. It's bottomed out unless there is pressure in the circuit.
    Now here is the problem. when you push in on the part around the pin it's possible that there is crud in the bore and it will damage the seal.
    If you have pressure in the front system you might be able to have somebody push the brakes and grab the pin with some vice grips when it pops out. If the system is completly out of fluid you may have to crack open the inlet lines on top and tap the thing with a wrench to dislodge the air.
    Best way to bleed these truck is rear first (side doesn't matter) then bleed driverside front then passenger side.
     
  9. imiceman44

    imiceman44 1 ton status

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    Alex
    When I open all the nipples I can get the fluid to go in the tubes faster but then each end that gets fluid to it I tighten.
    So now I have a full system with possibly some air bubles, I start bleeding the rear then the front.
    I only do that when I have all the system empty when I am replacing all the calipers or lines or when I do my bianual fluid change.
     
  10. Triaged

    Triaged 1/2 ton status

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    I often use gravity bleeding on my trucks. It worked really good when I did my axle swap and had zero fluid left in the system. I just opended up a rear bleeder and about 45min later fluid started comming out. Then I did the rest of the wheels. There was no air left in the system! It took a while but I was working on other stuff while it was flushing the system.
     
  11. R72K5

    R72K5 Banned

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    i always remove bleeder and put thuimb over hole and pump away at the pedal, this is how i do my master cylinders too i just mount the cylinder and leave the lines off and cover holes with thumbs and have someone pump away, its messy buy works quick and well

    for rear lines i always take off the 1/4" line at the rear axle hose and cover end of tube with thumb and pump away

    works good for when replacing entire rear line

    always bleed air out of the m/c first though

    this pin ordeal is sure complicated, you sure you can pull it outwards ? that doesnt sound like a good idea to me.....

    if the pin is bottomed out unless there is no pressure hten why is it outwards some at rest ?

    conmtradictory here.,,.


    any more info on this ?

    what are you really supposed to do with the pin when are manually bleeding with brake pedal pumps ?

    does anyone know ?
    for real ?
     

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