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Hot Rods AV8 brake help needed

Discussion in 'The Hokey Ass Message Board' started by hotrodrhp, Mar 27, 2019.

  1. hotrodrhp
    Joined: Sep 19, 2008
    Posts: 302

    hotrodrhp
    Member
    from Wisconsin

    The car is about 98% done and I have done virtually all the work on this build. However I have some concerns with the braking. Used hydraulic drums front and rear. Adjustable bias valve installed to balance system pressures,adjusted brakes and fully bled system. Problem is that I have a high pedal but it takes a "lots" of foot pressure to safely stop the beast. Installed power brakes on the 34 build but wondering if this is normal in this set up. Do the shoes need to be seated? Bias valve adjustment wrong? Any advice is appreciated.
     
    hfh likes this.
  2. theboss20
    Joined: Dec 30, 2018
    Posts: 230

    theboss20

    What year and what brake system? Did you check the fit of the shoes in the drums before you installed everything? Did you make sure the shorter primary shoe was toward the front on the vehicle? Is the master cylinder a match to the original brake system? Did you rebuild or replace the wheel cylinders?


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  3. Pete Eastwood
    Joined: Jul 27, 2011
    Posts: 991

    Pete Eastwood
    Member
    from california

    Pedal ratio ? Master cylinder bore size ?
    These things are important .
     
    RICH B and 55styleliner like this.
  4. 55styleliner
    Joined: May 11, 2015
    Posts: 558

    55styleliner
    Member

    Yeah, what Pete said!!! Pedal ratio and bore size are probably to blame.
     

  5. theboss20
    Joined: Dec 30, 2018
    Posts: 230

    theboss20

    I don’t recall any drum brake system using a bias valve...the master cylinder provided the balance between front and rear and the differential in the size of the friction material between front and rear provided the rest of the balance...65% front...35% rear...on average.


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    Chappy444 likes this.
  6. manyolcars
    Joined: Mar 30, 2001
    Posts: 8,400

    manyolcars

    Why did you add an adjustable bias valve? I've been working on old Ford's for 52 years and have never heard of that
     
  7. BJR
    Joined: Mar 11, 2005
    Posts: 6,796

    BJR
    Member

    A smaller bore master cylinder will give you higher brake line pressure, thus less foot pressure.
     
  8. hotrodrhp
    Joined: Sep 19, 2008
    Posts: 302

    hotrodrhp
    Member
    from Wisconsin

    Shoes and drums are matched sets . Standard Ford new master cylinder. Pedals from a mid Forties Ford. Think I had a brain freeze..... bias valve most likely the culprit. Stupid of me.... always over designing the wheel.
    Simple rerouting of brake lines. Guess I’m not quite there.


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  9. hotrodrhp
    Joined: Sep 19, 2008
    Posts: 302

    hotrodrhp
    Member
    from Wisconsin

  10. hotrodrhp
    Joined: Sep 19, 2008
    Posts: 302

    hotrodrhp
    Member
    from Wisconsin

  11. theboss20
    Joined: Dec 30, 2018
    Posts: 230

    theboss20

    No...


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  12. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,741

    V8 Bob
    ALLIANCE MEMBER

    Yes, if the brakes are over 40 years old. But residuals are good for any drum brake, regardless of age.
     
  13. town sedan
    Joined: Aug 18, 2011
    Posts: 1,290

    town sedan
    Member

    Two, or three things...
    "Standard Ford master cylinder" Don't think there is any such thing.
    What is the wheel cylinder bore size?
    What is the master cylinder bore size?
    Or, what was the original application for the master cyl & wheel cyl?
    -Dave
     
  14. Another example of poor information on brakes, the master cylinder does not provide balance between front and rear, it simply moves fluid, have a look at pascals law...and YES residual valves are required as V8bob said, unless the wheel cylinders have cup expanders, still will not hurt to have them.


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  15. theboss20
    Joined: Dec 30, 2018
    Posts: 230

    theboss20

    Guess I was thinking of a dual master...plus the residual valves are built in to the ports of a drum brake master...


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  16. Provided you are using a drum brake master to start with...., we don’t have nearly enough information to guess on his problem, need master cylinder and wheel cylinder dimensions as well as pedal ratio etc.


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  17. Chappy444
    Joined: Jan 27, 2012
    Posts: 1,227

    Chappy444
    ALLIANCE MEMBER
    1. Maryland HAMBers

    Since no one has asked yet, do you have any pedal free play? do you have the adjustable master push rod/eye bolt arrangement?
    Chappy
     
  18. hotrodrhp
    Joined: Sep 19, 2008
    Posts: 302

    hotrodrhp
    Member
    from Wisconsin

    I have free play at top of the pedal and the push rod is adjustable. Front wheel cylinder bore is 1.125 and rears are 1.065 inch bore Master cylinder bore is 1.625 inch bore. All are new pieces.
    I removed the residual valves and bias valve today ,re-routed fluid lines and bled the system. Pedals are unmolested 39-40 pedals. Frankly not much difference in braking.
    Need a "brake" from climbing under the car about now! Suggestions appreciated.
     
  19. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,741

    V8 Bob
    ALLIANCE MEMBER

    What kind and year drum brakes are they?
    Are you sure about the 1.625 master cylinder bore? That's a very large bore, and would definitely require a booster.
     
  20. murf 32
    Joined: May 30, 2013
    Posts: 66

    murf 32
    Member

    Try clamp the flexi hose to the rear
    Try the pedal then
     
  21. 31 Chopped Coupe
    Joined: Aug 24, 2014
    Posts: 97

    31 Chopped Coupe
    Member

    That master cyl bore sure sounds large to me. I would ditch the adjustable bias valve and just go with the stock Ford components. I used 39 pedals and master cyl and stock Ford wheel cyls for late forties backing plates plumbed with 1/4 inch brake lines. Stops great, couldn't ask for better performance from drums.
     
  22. hotrodrhp
    Joined: Sep 19, 2008
    Posts: 302

    hotrodrhp
    Member
    from Wisconsin

    Brake problem update....pulled the the drums from the car and this is what I found. Appears the shoes had high spots and that has limited shoe drum contact. Had high spots removed, readjusted the brakes and re bled the system. After much rain and some stupid spring snow here finally took the car out. Braking is remarkably better!!!!!
    Sometimes the simplest things are hardest to see. Thanks all for the input.
     
    theboss20 and town sedan like this.

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