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Technical Brake guru's

Discussion in 'The Hokey Ass Message Board' started by coilover, Feb 16, 2020.

  1. coilover
    Joined: Apr 19, 2007
    Posts: 623

    coilover
    Member
    from Texas

    Problem: brake builds pressure and locks up front disc brakes on 1937 Buick Special.
    Tried so far:
    New rubber lines (twice)
    New master cylinder with factory residual pressure brake line seats COMPLETELY REMOVED

    ZERO inline residual pressure valves. Did have 2# to discs and 10# to drums.
    Rod from pedal to booster has 1/4" free travel
    Rod from booster to MC has 1/4" free travel
    When cold pedal is only 1/3 of its travel off floor
    Kit is from Scarebird and uses Riviera rotors and Astro calipers.
    Brakes are perfect for first half dozen stops and then build till pedal is solid with no free travel and drag old straight eight engine down to a stand still.
    Only part not replaced is 7" dual diaphram booster.
    System worked fine for thirty years with drum/drum configuration.
    HELP!
     
    Last edited: Feb 16, 2020
  2. My brother's 57 Pontiac once did this. After checking everything I finally removed the master cyl and put it on the bench.........found the return port in the master had some gunk in it. Cleaned it out and voila! Worked fine then.
     
  3. alchemy
    Joined: Sep 27, 2002
    Posts: 16,090

    alchemy
    Member

    Is something heating up while you drive for a while? Is there a line near the exhaust somewhere?
     
    bchctybob likes this.
  4. David Gersic
    Joined: Feb 15, 2015
    Posts: 2,303

    David Gersic
    Member
    from DeKalb, IL

    You’re losing 1/2” of travel in the pushrods and it still works?

    Is it locking both wheels or only one? Crack a bleeder, see if it releases.



    Sent from my iPad using The H.A.M.B. mobile app
     
    bchctybob likes this.

  5. I'd start loosening things to find the last place the pressure releases. How did you figure the 1/4" between the master and booster?

    Sent from my Nexus 5X using The H.A.M.B. mobile app
     
    KJSR likes this.
  6. 67drake
    Joined: Aug 8, 2008
    Posts: 124

    67drake
    ALLIANCE MEMBER
    from Avoca WI

    Did you try contacting Scarebird? He is usually pretty good on follow up help.
     
    bchctybob likes this.
  7. Pat Thompson
    Joined: Apr 29, 2012
    Posts: 211

    Pat Thompson
    Member

    Wheel bearing too snug? Not allowing piston to be pushed back in caliper.
     
  8. bill gruendeman
    Joined: Jun 18, 2019
    Posts: 418

    bill gruendeman
    Member

    Is the caliper sticking and not moving back in so the pad stays on the rotor?
     
  9. what do you have to do to get them to release? does opening the bleeders solve the issue?
     
  10. earlymopar
    Joined: Feb 26, 2007
    Posts: 1,280

    earlymopar
    Member

    This symptom is most often caused by the piston in the cylinder not returning and therefore blocking the port. This is often a result of the push rod adjustment not being correct. Re-check your free-play setting but I'd start by backing the push rod off completely (no engagement of the push rod by the pedal arm) to allow the piston to return.

    - EM
     

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