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Technical disc brakes

Discussion in 'Traditional Hot Rods' started by coolieman, Jul 15, 2018.

  1. coolieman
    Joined: Jan 31, 2010
    Posts: 119

    coolieman
    Member

    Can 1caliper dragging slightly heat up fluid in the master cylinder to cause all 4 wheels to drag after 10 miles of driving on and off brakes,
    I have 4 wheel disc, corvette dual master cylinder,7 inch lower booster. ,there is 1/2 inch play in push rod, mike
     
  2. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,419

    Mr48chev
    ALLIANCE MEMBER

    Hot fluid shouldn't cause the problem you have. The wrong fluid might though.
    wrong residual valves? 10 lb rather than 2 lb? 1/2 inch play at the pedal? 1/2 at the pushrod would be excessive and probably beyond the travel of most master cylinders. Return spring on pedal? Pedal hanging up on something like the hole in the floor board? Had that happen on my truck at one time. Pedal would stick after you pressed it and let off.
     
  3. Since you already have way too much clearance on the pedal pushrod, maybe the the adjustment between the booster and master cylinder is tight. Easy way to check is loosen the booster, slip a body shim on bolts, and see if it works on a test drive. If works, just fix both adjustments.
     
  4. coolieman
    Joined: Jan 31, 2010
    Posts: 119

    coolieman
    Member

    had 2lb residuals took them out ,also I have heavy spring brake peddle I put a little extra clearance on pushrod to make sure it wasn't holding pressure also I can't figure out why I get higher brake pedal when hot the m/c can't be pushing peddle up cause it can't go any futher than back to stop ??? could the booster cause that ??
     

  5. fms427
    Joined: Nov 17, 2006
    Posts: 864

    fms427
    Member

    I’m with Rich B - check booster to MC pushrod


    Sent from my iPad using H.A.M.B.
     
  6. 29moonshine
    Joined: Dec 30, 2006
    Posts: 1,313

    29moonshine
    Member

    ^^^ i had a bad booster it was building pressure and applying the brakes. plug the hose going to the booster and drive it.
     
  7. DDDenny
    Joined: Feb 6, 2015
    Posts: 14,572

    DDDenny
    Member
    from oregon

    Had a mismatched m/c and booster, no free play in the intermediate rod, causing brakes to lightly apply on their own, shortened the rod about 1/8" and they worked great after that.
     
  8. 28TudorAZ
    Joined: Dec 29, 2016
    Posts: 114

    28TudorAZ

    I had the same issue. Swapped out the master cylinder and it went away.
     
  9. Ralphies54
    Joined: Dec 18, 2009
    Posts: 736

    Ralphies54
    Member

    I believe booster to master clearance at .030 and pedal to booster clearance 1/4" at most. Ralphie
     
  10. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,739

    V8 Bob
    ALLIANCE MEMBER

    There is no "free play" adjustment with the pedal push rod on a vacuum booster that I am aware of. Any perceived free play is the booster control valve initiating action.
    This requires the pedal, with it's own return spring, to have slightly more movement (when disconnected from the push rod) to ensure the booster can fully return.
    The booster output rod or pin should have +/- .040" free play with the master cylinder primary piston (unless specified otherwise) and this is checked with full vacuum applied to the booster, or about 20"Hg.
     
    Last edited: Jul 16, 2018
  11. coolieman
    Joined: Jan 31, 2010
    Posts: 119

    coolieman
    Member

    I unpluged booster hose and drove truck about the same distance as before came back to garage and jacked it up checked all wheels front turned free, rear just slightly tight, Does this show bad booster or booster rod needs adjusting??
     
  12. Ralphies54
    Joined: Dec 18, 2009
    Posts: 736

    Ralphies54
    Member

    Sounds like booster needs readjusting clearances. Is this booster above or below the floor?
     
  13. coolieman
    Joined: Jan 31, 2010
    Posts: 119

    coolieman
    Member

    I put two 1/8 shims between booster and master cylinder and hooked vacuum back up took it down road and it didn't lock up must have been clearance issue thanks all,mike

    L
     
    Blues4U likes this.
  14. I like the shim idea, great for diagnosing and easy to do.
     

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