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whats the wire on my proportioning valve for?

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

  1. Jaden

    Jaden Registered Member

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    have a misfit 84 I almost have together. Next thing is the brakes...how do I get them to bleed it says grab the clip and hold it or something is that the thing on the end?> does it come out or go in? what is the thing with the wire going to it in the middle for? HELP!!!
     
  2. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    That wire is for the pressure differential switch...
    That is, if there is a pressure change or difference between the two sides of the proportioning valve (front and rear) it activates the Brake warning light on the dash to let you know that there is a pressure differnce and your brakes could be failing!
     
  3. Jaden

    Jaden Registered Member

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    but its not connected to anything? is there a wire that should be connected to it that maybe just has come loose? it has a male terminal that is bolted to a bracket that is bolted to the frame. Also the switch to bleed the breaks "in-out is it the copper thing at the end?"

    thanks
     
  4. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    The wire that it should plug into ahould be off the harness for the head lights on the core suport.
    The button usualy has a rubber cap over it. it's possible the cap is gone. Should be a pin about 1/8 in diameter on the end that you press if the cap is gone. My guess is brass. It doesn't move much so if you feel it shift that's probably it.
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Believe its a tan wire, goes up to the firewall connector obviously. Will (or should) have a weather resistant connector (rubber outside) on it.
     
  6. mudddog91

    mudddog91 1/2 ton status

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    Just a question,have you personally pushed this "button" in for bleeding the rearrs?Just curious cause i treid to push mine in and it doesnt move.At least not the one under the rubber cap.My rear brakes still dont stop like they should so if youve got any ideas.........................
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    My understanding is the only time you should need to press that button is of you loose pressure on one end or the other it will equalize the pressure on both sides of the proportioning valve. I have never lost pressure so neve had to do it on my trucks but I have a spare that was loose in a box and it was stuck I had to put some serious mojo on it to get it to move and I'm not sure it poped all the way back out. it only moved maybe and 1/8 inch. It may pop out once you get some pressure back on the system.
    Now here is the worry. The last K5 rolled off the line 12 years ago. Brake fluid is supose to be changed every 2 years. Most people don't. The end result is the fluid becomes acidic and rust and crud accumulate in the system. It quite possible that valve will fail and leak, possibly internaly, and cause a improperly ballanced system.
    Several years back I spent $30 bucks on a cheapo hand pump vacume bleader kit (most parts stores have these). There are several advantages to bleeding this way. The biggest is you don't need to press that button on the bleeder so you limit your chances of it failing.
    You also don't risk bottoming out the master cylinder. Often you can cause the seals to fail internaly on the master if you bottom it with the old pump and hold way of bleeding. The seals will run on areas tham may have developed some rust of run over crud that is sitting beyond it's normal travel.
    If you can't get the brakes up to snuff buy bleeding and adjusting (the rears should drag and have resistance when you try to spin the drum by hand) don't fool around. Take it some place and have them power bleed and pressure test the system. They will be able to tell you if the master is bad. If you want to gamble then gamble on the master. Rebuilt masters can be had for around $40 with a life time warranty on pre ABS trucks.
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Any time you bleed the brakes your brake light should come on as presure is lost on one side of the system. (try with the key on)

    I don't disagree, that button is a "release" to re-center the prop valve internals, and the manual states this IIRC. I know the manual states that once you build pressure, the prop valve SHOULD re-center itself.

    Never needed it myself when manually bleeding numerous GM vehicles, I assume its for gunked up systems like you mention.
     
  9. Jaden

    Jaden Registered Member

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    Ok then my next stupid question would be, why cant I get the rear brakes to bleed? either with the hand vacuum pump or the old two man method. I can get my truck to stop using fronts only "still getting it all built" but I cannot get the rears to pump up at all.
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    So you know the rears are the problem because...? I'm assuming it's because you aren't getting any fluid to pump out of the rear bleeders?

    I'm not sure how bleeding reacts if the rear brake shoe adjuster (that star wheel) is in so far that the shoes don't forcefully contact the drum...I guess if the rear adjusters were that far out, you might be able to run out of pedal travel before the shoes moved out to the drum or something...seems like that would be VERY unlikely though. Can you get a firm pedal at all, or is it always spongy?
     

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