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    Stock brake bias valves? What do they do?

    <edit- this is as applies to race cars, not street cars, thus, track and auto-x>

    So the non- abs cars have 1 or 2 discrete valves in the brake systems.
    2 in my case. (2-87)

    What, if anything, are they supposed to do?

    I always thought they were limiters on the rear circuit, to pull some
    pressure off (or limit it) after a certain point. But:

    I put gauges front and back, and stood on the pedal, and I get pretty
    even pressure all the way to 2000 psi. There might be a slight tapering
    off of the rears above about 1500, but it'd be 25% or less if it was anything.
    (for reference, all 4 are locked above about 1000psi line pressure, just
    by the 'oh-shit-ometer' in my right foot. At 2000, I've got #200 on the
    pedal and the booster's doubling that)

    Given that the piston area split in the calipers is damn near ideal at
    70/30 anyway, I'm planning on pulling the stock
    valves and putting a simple line- limiter on the back- and setting it
    to about #500, to start. Because I'm sick of rear brake lockup.
    And we're not allowed dual masters.
    Even with Hawk DTC 60 in front, HT 10 in back, it'll still grab the rears sometimes...

    Interesting thing discovered- the booster adds something around #1000 psi
    to whatever you are doing with your right foot. Then it's all done, and it's
    down to your foot to generate anything more you might need.

    Another interesting thing- #100 on the pedal translates to about #500
    psi at the calipers.

    A very uninteresting thing- I need to work out more.

    But I'm curious to know what the valves are SUPPOSED to do.

    t
    now, sometimes I just mess with people. It's more entertaining that way. george graves

    #2
    The stock bias valve is supposed to limit pressure to rear brakes. It has been a while since I've seen the curve, but from memory it only allows about 600psi to rear brakes regardless of line pressure. It sounds like the one you have isn't working.
    The car makes it possible, but the driver makes it happen.
    Jim Levie, Huntsville, AL

    Comment


      #3
      600psi??? Ok, thanks, that explains a lot!

      http:// http://www.e30tech.com/forum/showthread.php?t=68770&page=6

      http:// http://forums.bimmerforums.com/forum/showthread.php?1598190-How-does-the-brake-bias-valve-work&p=21266451&posted=1

      After too much more reading, I found the above. Ironically,
      I have the same 4- port valve that Ranger does. Obviously, tho,
      mine is shot.

      t
      Last edited by TobyB; 05-18-2014, 10:18 PM. Reason: massive internet "research".........
      now, sometimes I just mess with people. It's more entertaining that way. george graves

      Comment

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