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Brake Warning Light

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by NuBombs72K5, Nov 27, 2001.

  1. NuBombs72K5

    NuBombs72K5 1/2 ton status

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    After replacing all of the instrument panel bulbs, I find the brake warning light will not go off. When I take the wire off of the proportioning valve, the light goes out. My stoplight switch is new and there are no burnt bulbs. I don't seem to have any braking problems, so I don't know why this light is on. Does anyone have any Ideas.
     
  2. Ryan B.

    Ryan B. 3/4 ton status GMOTM Winner

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    Duuude.
    We're assuming you don't have any brake lines leakin'.
    That wire goes to the Pressure differential warning switch on the proportioning valve right.
    The purpose of this is to activate the warning light if either the front or rear loses hydraulic pressure.
    You said that if you disconnct it there at the switch on the p.valve and open the circuit the light goes out.
    I'll bet you $10 that if you reconnect that wire to a good ground the warning light on the dash will come on again.
    This means your bulb and all the wiring is GOOD.
    Check the connection good, make sure it's not shorting to ground somehow.
    The pressure differential warning switch in the proportioning valve must be bad. The contacts are probally stuck.
    My 2 cents.
     
  3. Triaged

    Triaged 1/2 ton status

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    I aguree...Either the prop valve is bad or you have a hydrolic leak somewere. I would bet on a leaky rear wheel cylinder or a bad master cylinder. Make sure you pull back the dust boot on the wheel cylinder to see if it is leaking.

    '71 Blazer CST w/ a 400sbc, 4" lift, 36" Supper Swampers, and alot of rust
    <a target="_blank" href=http://community.webshots.com/user/triaged>See it Here </a>
     
  4. Steve_Chin

    Steve_Chin 1/2 ton status

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    The "Switch" in the combination valve is nothing more than a metal spool and a couple of seals. The metal spool rides against the inner bore of the combination valve. If the combination valve's bore becomes rusted (or if the spool rusts) and the spool is shifted to one side or the other for any reason (including bleeding the brakes), the spool will become stuck against the pin that protrudes down from the contact to which the tan wire is connected. Un-sticking it is a relatively simple job of disassembling the combination valve, cleaning it, and putting it back together.
     
  5. NuBombs72K5

    NuBombs72K5 1/2 ton status

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    That is probably the problem. I don't have any leaks or brake problems. I replaced the master cylinder a while back as well as the calipers and the brakes have been great. I'll check to wire and then try cleaning it up like you said. Thanks for all the quick replies.
     

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