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"BRAKES" light

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Jonathan, Apr 16, 2001.

  1. Jonathan

    Jonathan 1/2 ton status

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    \"BRAKES\" light

    The "BRAKES" light on the dash of my 77 K5 comes on during hard braking. Does this mean I need to add brake fluid or need new brakes or what?
     
  2. Goose

    Goose 1/2 ton status

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    Re: \"BRAKES\" light

    That light is activated by the switch in the combination valve(proportioning valve). It means that there is a pressure difference from front to rear that shouldn't be there. This is caused by the seals in your master cylinder going out.

    You need to replace your master cylinder.

    It can last a while longer, but why push it on something like brakes.

    [​IMG]
     
  3. Jonathan

    Jonathan 1/2 ton status

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    Re: \"BRAKES\" light

    I just bought it friday and the guy I bought it from said he redid the brakes last (pads, shoes. ect.) and said it probably needs new drums in back. Could that be it? I think I can probably do without rear brakes for a while.

    <P ID="edit"><FONT SIZE=-1>Edited by jonathan on 04/16/01 07:38 PM (server time).</FONT></P>
     
  4. Jonathan

    Jonathan 1/2 ton status

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    Re: \"BRAKES\" light

    Where can I get a new master cylinder or can I rebuild my old one?
     
  5. Goose

    Goose 1/2 ton status

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    Re: \"BRAKES\" light

    If it has new shoes, but the drums need replaced, that shouldn't cause your brake light to come on. I would take the drums off and see what kind of shape they are in.

    [​IMG]
     
  6. jimmyjack

    jimmyjack 1/2 ton status

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    Re: \"BRAKES\" light

    I dont think master cylinders are too much. Less than 30 bucks.

    "My blazer may be slow, but it goes faster at higher speeds"

    Jim
     
  7. Goose

    Goose 1/2 ton status

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    Re: \"BRAKES\" light

    They sell rebuild kits, but for the price of a rebuild one plus the time you save, the rebuilt ones are the way to go. Any auto parts store has them.

    [​IMG]
     
  8. Jonathan

    Jonathan 1/2 ton status

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    Re: \"BRAKES\" light

    Could I get a used one at a junk yand or something? If so, what years and models used that specific master cylinder? I have a 62 C10 at my disposal but I really don't think that would work.
     
  9. Jonathan

    Jonathan 1/2 ton status

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    Re: \"BRAKES\" light

    Thank's, I'll check out the rebuilt ones, I have to get a new reverse light anyway.
     
  10. Goose

    Goose 1/2 ton status

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    Re: \"BRAKES\" light

    I wouldn't go the junk yard route. Brake fluid attracks water, and one sitting in the junk yard won't have typical use or maintenace and would likely not last long. The 62 C10 would be wrong. Any 1/2 ton chevy/gmc truck/blazer/jimmy from about 73 to 87?? should work. Maybe not that much of a range.

    [​IMG]
     
  11. Jonathan

    Jonathan 1/2 ton status

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    Re: \"BRAKES\" light

    I didn't think the 62 would work but I thought I'd ask just in case. Thank's for your help.
     
  12. Triaged

    Triaged 1/2 ton status

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    Re: \"BRAKES\" light

    It could also be something besides a master cylinder. A leaking caliper or wheel cylinder could also cause the brake light to come on. My guess would be the wheel cylinders in the rear (if going bad and new shoes are put on sometimes the seals go real quick after becouse of being moved from where they were). Pull off the wheel and drum and check under the dust boot for fluid. If there is any on fluid on either side rebuild or replace both (rebuild kits are about $5 each)

    '71 Blazer CST with alot of rust
     
  13. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: \"BRAKES\" light

    He's right...even low fluid or air in the lines can cause this..all that is needed for the brake light to come on is a difference in pressure between the front and rear brakes, IE air in the system, leak, low fluid, etc.


    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     
  14. Jonathan

    Jonathan 1/2 ton status

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    Re: \"BRAKES\" light

    I checked the fluid in the master cylinder and it was full to the top then drove around in a very hilly neighborhood this afternoon and gave the brakes a real good work out a the light didn't come on one single time. I don't know what the deal is. It will be a while before i get enough time to check the drums. But I know there is no bad leakage.
     
  15. dyeager535

    dyeager535 1 ton status Premium Member

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    Re: \"BRAKES\" light

    From what I could tell from the factory service manual, the proportioning valve SHOULD re-center itself when the problem is corrected and pressure is applied. Even when bleeding the brakes, if you leave the key in the "run" position, the light should come on, since there is a pressure "leak" in the system, which should move the proportioning valve trigger internally, activating the brake light. According to GM, if you lose the front or rear half of the brakes, the end that didn't fail should still work. But I've heard of that not happening and losing all braking. Don't think I'll test that one.

    Dorian
    My K5 and Chev/Olds tech/links page: <A target="_blank" HREF=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</A>
     

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