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Proportioning valve?

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by skyblazer, Feb 13, 2002.

  1. skyblazer

    skyblazer 1/2 ton status

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    During my daily test-drive I noticed that my rear brakes will lock up when I get on em hard. The master cyl is new, bled properly and I have no air in the lines, which leaves the prop. valve. I believe this was the topic of a previous post, but I can't find it. Is there a special way to bleed it? Any thoughts? Also the brake indicator light (dash) doesn't work, how can I test/fix this?

    <font color=blue>As my truck gets higher my balance gets lower!<font color=blue>[​IMG] <font color=red><a target="_blank" href=http://coloradok5.com/gallery/albuo72>PICS</a></font color=red>
     
  2. frito

    frito Registered Member

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    what do you mean the brake light doesnt work? are you thinking that its supposed to light up when you put on the E-brake? as far as i know thats not what it does .. mine works on my 71 K5 and that light is hooked up to the prop. valve witch is accualy called a combination valve because it has 2 functions 1st . it keeps the front brakes from working untill the rears have met resistance from the drum so your rears wont turn on first and lock up easily and 2nd it detects line leaks and the BRAKE light on the dash will come on when a leak in the lines is detected ... i have this problem =) one of my rear lines or wheel cyl. leaks and the combo valve thinks that the rears arnt working and when im half way though my pedal stroke it finaly lets the front brakes work best thing i can say for your rears locking up is to check the adjustment on them ... you prolly need to close the adjuster some so they arnt so close to your drums
    good luck!

    71 K5 Blazer,350/TH350/205 33's/ 2inch lift for now, soon to have 14B FF and D60 in a few weeks
     
  3. skyblazer

    skyblazer 1/2 ton status

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    No, what I meant about the brake light was that when I bled the rear liines (bleeder open and brake depressed) the light would not come on. It should come on right? Also, I used a meter and the wire to the combo valve has no voltage..should it? I'm assuming that during a leak, the piston between the front and rear systems would move and ground itself to activate the warning light.

    <font color=blue>As my truck gets higher my balance gets lower!<font color=blue>[​IMG] <font color=red><a target="_blank" href=http://coloradok5.com/gallery/albuo72>PICS</a></font color=red>
     
  4. skyblazer

    skyblazer 1/2 ton status

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    I finally found the post about bleeding the combo valve!! I understand that the metering pin or button must be held in during bleeding to prevent the front or rear system from being shut off. Mine bled fine without doing this......could the spool/piston in the valve be stuck? Could this cause uneven braking between the front and rear? I suppose I should see if the pin can be moved, this would tell me if the piston was free.

    <P ID="edit"><FONT class="small">Edited by skyblazer on 02/14/02 02:55 PM.</FONT></P>
     
  5. frito

    frito Registered Member

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    yeah i see .. i dont think mine came on when i bled the brakes but i guess what your saying is possible ... ohh but another thing when i bled my fronts i never pushed that button too and they bled just fine
    i have have been thinking about removing that damned combo valve and putting one in from a later year truck ... or just not having one! hook the lines straight to the MC it would fix my problems and maybe yours too =)

    71 K5 Blazer,350/TH350/205 33's/ 2inch lift for now, soon to have 14B FF and D60 in a few weeks
     
  6. skyblazer

    skyblazer 1/2 ton status

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    OK, no more drivin on busy streets until I get the brakes figured out. I got a yellow light at a busy intersection and got all squirly trying to stop. Frito, I pulled the rear drums off and turned back the adjusters a few turns. That makes sense that if the rears are too tight that the fronts may not engage properly. The brakes are new and come to think of it, I think I adjusted them out several turns. I'll test drive it tomorrow.....on an empty road!!!

    <font color=blue>As my truck gets higher my balance gets lower!<font color=blue>[​IMG] <font color=red><a target="_blank" href=http://coloradok5.com/gallery/albuo72>PICS</a></font color=red>
     
  7. 72THING

    72THING 1/2 ton status

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    Interesting. I didn't know what that wire was for on the proportioning block. I just left it hooked up, but my wiring was hacked up by previous owner and I figured theres no telling where it leads to now. It may not go to any thing. Can someone shed some more light in the little pin thingy that the wires hooked to or whatever ya'll are talking about?

    Thanks,

    Will

    '72 C10, originally 2WD, 6"Springs f+r, Dana 60 f+r, Lock-Right front, welded rear, 4.56s, 350, SM465, NP205, 39.5" TSLs, ORD crossover steering
     
  8. californiak5

    californiak5 1/2 ton status

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    That goes to a warning lite in the dash. It tells if there is any loss in brake pressure somehow and warns you about it. Mine would go on and off every once in a while. I came to find out that I had a leaky master cylinder. I changed it out and havent seen the lite on the dash since [​IMG].

    See Ya,
    Keith

    "Your just mad cause the voices only talk to me."

    <a target="_blank" href=http://coloradok5.com/gallery/californiak5>CaliforniaK5's Pictures</a>
     
  9. skyblazer

    skyblazer 1/2 ton status

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    Thing, the wiring is connected to the middle of the combo (proportioning) valve. The other "pin" we're talking about is the metering pin or button in the front of the combo block. From what I gather on the forum, this is used to hold the piston in the valve body in a centered position during bleeding. There is a lot of info out there if you do a search on "combination valve" and go back a several months.

    <font color=blue>As my truck gets higher my balance gets lower!<font color=blue>[​IMG] <font color=red><a target="_blank" href=http://coloradok5.com/gallery/albuo72>PICS</a></font color=red>
     

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