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Technical Hard pedal, touchy brakes

Discussion in 'The Hokey Ass Message Board' started by lincolnlog, Jun 29, 2014.

  1. lincolnlog
    Joined: Feb 25, 2007
    Posts: 186

    lincolnlog
    Member
    from Arizona

    So I switched the old treadle vac out of my 60 continental in favor of a dual 7" booster and a .75 bore dual master. The treadle vac bore was around .65 or so, but the old treadle vac had less power assist ~6" single diaphram.

    The pedal is somewhat stiff for the first 1" or so of travel until the brakes engage, but once they do, the brakes are very responsive.

    The car has a great big vacuum resivour that isn't connected now. Stock 430 motor 18-20" vacuum at the manifold. Vacuum assist line is hooked up to manifold.

    Any ideas why the first 1" of travel is soo stiff?
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 48,271

    squirrel
    Member

    wild guess is the master cylinder bore is way too small for a good booster with drum brakes.
     
  3. lincolnlog
    Joined: Feb 25, 2007
    Posts: 186

    lincolnlog
    Member
    from Arizona

    The new MC is actually larger than stock, which would explain a stiffer pedal when the brakes engage, but I'm puzzled why it is stiffer before engagement?
     
  4. Mr48chev
    Joined: Dec 28, 2007
    Posts: 28,791

    Mr48chev
    ALLIANCE MEMBER

    I'm inclined to go along with Jim on this. That small bore is going to put a lot more pressure than a 1 inch bore master cylinder would.
    As for the binding or tightness in the first inch, is it possible that the geometry of the pedal, pushrod and booster/master cylinder are off a bit? If the pushrod isn't being pushed in perfectly straight it may be pushing the piece it pushes against off to one side just a fraction causing more friction until you get past that point.
     

  5. lincolnlog
    Joined: Feb 25, 2007
    Posts: 186

    lincolnlog
    Member
    from Arizona

    Hmmm...I'll measure the pushrod angle
     
  6. alittle1
    Joined: Feb 26, 2005
    Posts: 314

    alittle1
    Member

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