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Brakes ... again!

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by backlash, May 14, 2001.

  1. backlash

    backlash 1/2 ton status

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    When I stomp on the brakes ... I hear a "gush" of air and the pedal travels 2-3 inches before I get response at the wheels. Is there some sort of piston or something between the brake pedal and the booster?

    Could this be related to the check valve at the booster? Sound is loud and definitely under the dash, not behind the firewall. When letting up on the pedal I hear a squeak behind the firewall sounds like air leaking more than hydrolics. Any suggestions?
     
  2. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    Sounds like the power brake booster has a problem. Do you think it can be forcing the air through the firewall as the mechanism in the booster collapses....?
     
  3. backlash

    backlash 1/2 ton status

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    You know ... I was thinking at first no way (the booster and master cylinder are brand new), But then I was thinking. Maybe that damn $20 check valve has something to do with it. Just got off the phone with the parts guy at the dealer.

    Does pushing on the brake pedal push the rod towards the master cylinder or pull it towards the cab? Not sure if it's direct or if it pivots.

    I mean which direction does the piston in the M/C apply to the wheels?
     
  4. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    I think it is a pusher system all the way.
    If all the boots are good, I think a quick depression of the pedal would funnel air back into cab - could just be speaking outa my arse cuz never experienced this one. There is always a liitle noise but you are speaking of a change....?
    The closest scenario I had was by switching to synthetic fluid- lost lots of peddle. Later found out that since it is more slippery than regular fluid, some efficiency is lost in the master cylinder. Synth doesn't collect water tho.
    I ramble. Keep us posted.
    Dave
     
  5. backlash

    backlash 1/2 ton status

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    This has been going on for about 2 years and started gradually ... have taken it several places, but no luck!

    What boots are you speaking of?

    Thanks
     
  6. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    I think there is supposed to be a boot on the cab side of the power brk unit.
    Other thoughts.
    Have you evere had the brake system power bled? You might want to try that. How much everyone?
    Also master cylinders can lose efficiency after many miles -
    hardened rubber and wear spots in the cylinder that let fluid by - what I've been told anyway.
     
  7. backlash

    backlash 1/2 ton status

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    I can't seem to find any info on that boot. Not sure how to research this. Is it pressurized? Would explain the excessive travel.

    The M/C has been replaced 3 times in 2 years by the dealer ... I should hope they power bled the brakes. Is it possible that the excessive free travel is tearing up the M/C internally?

    Thanks again ... this must be a boring topic for some ...LOL

    HELP!
     
  8. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    If it is not my imagination, I am thinking that it is just a dust boot.
    And the boot is not a problem or symptom - was just an idea on why you were hearing 'whoosh' in cab.
    Free travel should not be harming anything but we need to determine if the 'free' is normal or a problem.
    How old are your pads/shoes? Do you have stock tire size? What about the check valve you mentioned? Why do you think it may be related?

    The basics:
    -resurface rotors-a glazed rotor is also more 'slick' then a fresh rotor. Extra force (pedal travel) will be required to get normal braking. There is a post on turning ideas <A target="_blank" HREF=http://www.coloradok5.com/forums/showflat.pl?Cat=&Board=blazer4x4&Number=138087&page=0&view=collapsed&sb=5>http://www.coloradok5.com/forums/showflat.pl?Cat=&Board=blazer4x4&Number=138087&page=0&view=collapsed&sb=5</A>. Go for the on the vehicle option if you can.
    -flush the system with new brake fluid. I would not use synthetic.
    -Bleed, bleed, bleed. Some post here mention needing QUARTS to finish. I have done it with 1. Options include powere bleed.
    -adjust the back (assuming shoes). More power, less volume of fluid.
    Are any of our brethren in your area? You need to compare.

    Since everything is new, I think you need to adjust and bleed etc.... This can all be air in the lines.

    ANYBODY ELSE?

    Dave
     
  9. backlash

    backlash 1/2 ton status

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    Dust boot ... stopped by the parts department yesterday and got an exploded view of the system ... don't see a boot. The woosh sounds like a bad shock absorber or pushing on a bicycle pump with nothing attached ... no seals or something.

    Everything is new and/or stock ... no mods.

    I replaced the check valve yesterday ...and although the booster was replaced and I originally thought the valve had not ..in fact it had (I'm pretty sure). It brakes correctly when cold at least today.

    Still have the woosh and the squeak when you let the pedal up. But much better.

    Guess I need to try another post to see if that is normal. Thanks for all the interest.

    Bicycle Bob
     

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