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Need some schooling- rear height-sensing proportioning valve

Discussion in 'The Garage' started by Can Can, Jul 17, 2006.

  1. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Can anyone explain to me how the rear height-sensing proportioning valve works on my 89 V3500? Does it need any periodic maintenance or adjustment? :confused:
     
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    My understanding is this...as you load weight onto the truck the arm lowers. That arm is like a flow control valve for the amount of rear braking you're going to get. More load, more rear braking. Light load, less braking in the rear. I don't think there is much you can do as far as maintenance on it. Maybe hit the pivot points with a bit of lube now and then...

    Rene
     
  3. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Yep, what Rene said. :thumb:
     
  4. ntsqd

    ntsqd 1/2 ton status

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    Pressure rather than flow, but yep, what he said. Think of it as a load directed variable Proportioning Valve.

    About the only adjusting is fine tuning it if you want to match it to a known loading.
     
  5. neverendingproject

    neverendingproject 1/2 ton status

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  6. K5er4Life

    K5er4Life 1/2 ton status

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    When I did a 4" lift on my crew I ended up using a 2" block in the rear to level the truck out. I just removed mine because I was too lazy to "adjust" the arm longer 2 inches. I havent been able to tell a difference stopping from before and after it was removed. I would venture to say it probably was so old it didnt work but my crew cab is in really good condition.
     
  7. HarryH3

    HarryH3 1 ton status Author

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    The only time you would notice is in a full-on panic stop. The valve is supposed to prevent the rear wheels from locking up first. A truck with an empty bed needs way less braking out back than a fully loaded one needs. You won't notice a difference in normal braking.
     
  8. sled_dog

    sled_dog 1 ton status

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    it definetally does something too.... the previous owner of my Burb broke the fittings off in the valve so he bypassed it. That thing would lock up the rear tires in a heartbeat.
     
  9. 79k20350

    79k20350 3/4 ton status

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    wow i never knew what that was before...learn something new everyday:D
     
  10. sled_dog

    sled_dog 1 ton status

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    only on some vehicles. 3/4 and 1 tons. My Burb was a 2500, so it had it.
     
  11. 79k20350

    79k20350 3/4 ton status

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    My k20 had it. it wasnt hooked up, just the arm off the diff. I have seen it on a few 3/4 and 1 tons since though. i never knew what it was and wound up just unbolting it. I had a few panic stops in that truck but the rear never really locked up (and the brakes were good too)
     
  12. K5er4Life

    K5er4Life 1/2 ton status

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    I locked up my 37"s on the freeway doing about 55mph and the truck stopped great. :eek1: Some dip lady pulled out in front of me on the freeway. It was a hard stop and started to go out of my lane but I was trying to steer away from her. It felt as though the front and rears locked at near the same time. Before I made any mods to the truck (lift, tires, and removal of valve) I also had another hard stop and the truck felt exactly the same. And that was with radial dually tires.

    Im very impressed with the way the hydroboost stops the truck, in fact I cant believe how well the crew cabs take lifts and tires. Other than sitting a little higher there hasnt been a huge noticeable difference in ride, stopping, turning, performance, or anything thats usually associated with lift and tires. But I only did a 4" lift so that may have alot to do with it. :D
     
  13. Goose

    Goose 1/2 ton status

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    I bypassed mine when I put new rear brakes on.
    Haven't had any problems with the rears locking first.
    Testing on sand/gravel roads showed the front tires still locked first.

    On a side note, just had to replace the passenger side rear brake line.
    Good thing for dual resivoir master cyclinder. I was able to make to the parts store and back home without too much trouble.

    It did take a lot more pedal travel to stop and I held my foot over the e-brake just in case. $7 for brake fluid and a line, not too bad.
    Bent it myself, hooked up the mitivac and bled it. About 2 hours in all.
     

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