Barely any brakes, I'm stumped.

Discussion in 'The whoa and the sway.' started by ancientx, Sep 1, 2019.

  1. ancientx

    ancientx horn/antler&bone carver

    Background:
    66 Lark, originally single resevoir master cylinder/booster with drum brakes. The booster shot craps so my uncle and I replaced it with a "Corvette" style (his words) dual resovoir an 9inch booster which was brand new in the box. It was bench bled and the brakes worked great for 2 years.
    The Lark has sat for 8yrs since then.
    I've rebuilt the wheel cylinders, replaced the front brake hoses and bled d@mm near a quarts worth of fluid through the lines.
    I double checked that all lines and bleeder valves are tight.
    I also removed the vacuum hose to the booster, inspected it, passing muster, I reinstalled it.
    The pedal still goes almost to the floor and barely stops the car.
    I also inspected for leaking lines, none.
    Any ideas?
     
    Last edited: Sep 2, 2019
  2. gsx455-4ever

    gsx455-4ever Gold Level Contributor

    Did you " bench Bleed " the Master cylinder ???
     
  3. ancientx

    ancientx horn/antler&bone carver

     
  4. Nailhead

    Nailhead Gold Level Contributor

    Master cylinder leaking internally is a possibility.
     
  5. buick64203

    buick64203 Just plum crazy Staff Member

    Stupid question- did you make sure the rod in the booster is up against the reciever cup on the master? Some corvette style/ bathtub style masters have a deep receiver cup for extra long booster rods. So in other words, you may be pressing the pedal to the floor but the piston in the master might be hardly getting depressed
     
    mrolds69 likes this.
  6. Dr. Roger

    Dr. Roger Stock enthusiast

    Try the simplest thing first...bleeding. Bleeding the air in the rear lines can be a real issue. I've gotten air in those lines after replacing components that made me pull my hair out. I learned when bleeding, pump the brakes 3-5 times then hold before opening the valves. This seems to help get those stubborn bubbles out.
     
  7. ancientx

    ancientx horn/antler&bone carver

    Yes
    Yes, we had. I drove it for 2 years no problems, then it sat for 7.
     
  8. ancientx

    ancientx horn/antler&bone carver

    *sigh* That's what I've been doing. I got nothing in this one, I'm stumped.
     
  9. BuickV8Mike

    BuickV8Mike SD Buick Fan

    Can you "pump up" the brakes gaining a firm pedal up off the floor?
     
  10. ancientx

    ancientx horn/antler&bone carver

    Nope. It goes most of the way to the floor before stopping.
     
  11. BuickV8Mike

    BuickV8Mike SD Buick Fan

    Most of the time when you have air in the lines you can quickly pump up the brakes to get a firm pedal up off the floor while a single push firms up at the floor.
     
  12. BuickV8Mike

    BuickV8Mike SD Buick Fan

    When you rebuilt the rear brake cylinders, did you properly adjust the pads for proper drag with the drums?
     
  13. ancientx

    ancientx horn/antler&bone carver

    I thought I did.
    Adjusted the star wheel until the drums were rubbing on the shoes. I then had a busy step on the pedal and tried turning the drum by hand, if it didn't lock up, I did it some more.
     
  14. BuickV8Mike

    BuickV8Mike SD Buick Fan

    With no brakes on the rear wheels should only make one turn and stop when spun hard.
     
  15. Dr. Roger

    Dr. Roger Stock enthusiast

    Are you getting a good strong burst of fluid at all 4 wheels when you open the valves when bleeding? If it is just a trickle, it could be air in lines, clogged lines, bad master cylinder, etc. I can't remember if a 66 had the rear rubber hose. Sometimes, those collapse inside when they get old and don't allow fluid to the rear brakes. If the flow is about the same at all wheels, then it could be the master.
     
  16. Electra man

    Electra man Older and Slower

    Internal seals in master cylinder hardened and are not making a pressure seal. Rebuild or replace it. You've already done everything that should firm up the pedal. It's somewhat rare for a replacement master to last 10 years with regular use, yours is already 10 and stale from non use.
     
    ancientx and Briz like this.
  17. Briz

    Briz Platinum Level Contributor

    Exactly what I was thinking
     
  18. ancientx

    ancientx horn/antler&bone carver

    Strong pressure, large volume of fluid.
     
  19. Dr. Roger

    Dr. Roger Stock enthusiast

    I guess I would replace the master, then bleed the crap out of it and see if that helps. Sounds kind of like the wheels are getting fluid but the shoes aren't doing their thing. No oil or glaze on the pads? Had a Nova that did the same thing (4 wheel drum). Ended up being air in the line that took a lot of work to get out. But yeah, it is a stumper.
     
  20. ancientx

    ancientx horn/antler&bone carver

    *sigh* Well, I have been eyeing that new MC Baer came out with. :)
    Could the booster have shot craps also?
     

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