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Master Cylinder Problems

Discussion in 'The Hokey Ass Message Board' started by bigalturk1, Mar 31, 2011.

  1. bigalturk1
    Joined: Sep 23, 2010
    Posts: 369

    bigalturk1
    Member

    Help!
    I have Manual brakes on my 39' Ford Coupe.Twenty-two years ago I built it and I used it weekly. The Front brakes are Granada Discs. The rears are regular 10" drums (Bronco 9") with 13/16" wheel cylinders. I was running a 75' Nova master cylinder (Under the floor) that has a 1-1/8" bore. I finally deceided to change it because the pedal pressure was to hard for my wife to drive the car and, it never really stopped good enough to lock the brakes. I purchased a Monza (3/4") master cyclinder and installed it. I am runnning 1/4" brake line out of the front and rear, master cyclinder outlets. I have a 2 pound Residual valve going to a "Line - Loc" and a 1/4" line going to a T connector and two 3/16" lines splitting off to each front brake.
    For the rear brakes I have a 10 pound residual valve going to an adjustable pressure control valve going to a 1/4" line to the rear axle and splitting to 3/16" line to each rear brake cylinder... then I bleed the system.
    The Brake pedal now goes to the floor. On Jackstands, with the brakes applied, the front brakes lock and I can't turn the front tires by hand. However, with the Rear brakes applied, I can turn the rear tires if I apply some grunt. So... needless to say, I can't drive the car now.
    Sould I try switching the 1/4" lines out of the Master Cylinder to 3/16" inch or should I try a 7/8" or 15/16" or 1" master cylinder? I really don't want to run Power brakes!
    Any good ideas appreciated...Thanks.
     
  2. i would try a 1" master. changing the lines won't make a difference.
     
  3. Bigdaddyhemi
    Joined: Sep 1, 2010
    Posts: 361

    Bigdaddyhemi
    Member

    Is your adjustable porporiting valve open all the way?
     
  4. Normal Norman
    Joined: Aug 9, 2006
    Posts: 510

    Normal Norman
    Member
    from Goshen IN.

    Have you checked the condition of the rear brakes? Or, adjusted the rear brakes? It is hard to bleed a M/C under the floor, could that be a problem? And do you have the large resivour on the M/C plumbed to the front brakes and the small res. going to the rear brakes? Just some thoughts, Normal Norman
     
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  5. JohnEvans
    Joined: Apr 13, 2008
    Posts: 4,883

    JohnEvans
    Member
    from Phoenix AZ

    Plus 1 here . The line size doesn't make any diif,but you went WAY to small on the M/C.
     
  6. budd
    Joined: Oct 31, 2006
    Posts: 3,478

    budd
    Member

    if you still have your old parts could you just change your pedal ratio?
     
  7. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,589

    V8 Bob
    ALLIANCE MEMBER

    Normally you can't go any smaller than a 1" master on a '39-'48 Ford without the pedal bottoming out before the master. You'll never completely bleed it, or have the full advantage of a dual master if you can't fully stroke the master. The stock '39 master had a 1 1/16" bore, so you went from one extreme to the other. The others also gave good advice-make sure the rears are correctly adjusted, and the prop valve is in (open) all the way. Line size has nothing to do with it, although 1/4" is not necessary or needed, as brake fluid "shuttles" back and forth, not flows.
     
  8. Vimtage Iron
    Joined: Feb 28, 2010
    Posts: 515

    Vimtage Iron
    Member

    If all worked fine before then it would seem that changing from an 1 1/8 to a 3/4 is the problem, there is not enough fluid movement to make things work correctly, you'll need to go back to an 1 1/8 and maybe use a midland booster remotely mounted, also change the lines to 1/4 instead of 3/16 that may have been some of the problem before. 3/16 is too small for that.
     
  9. Well your too far for me to come over and take a look at it so just better swap me for my stude. The brakes don't work on it yet either so you won't be out much. :D:D

    Probably need a bigger bore master although the monza should have been a drum disc setup. Did you bench bleed the master? Are your rear brakes adjusted up or are the shoes really worn?
     
  10. ECIGUY
    Joined: Feb 24, 2009
    Posts: 111

    ECIGUY
    Member

    The Granada calipers are the same piston diameter as a Mustang II, 2-19/32 in. 79-81 Mustangs ran a 7/8 bore m/cyl. unboosted. If you are in the 5 to 5-1/2 pedal ratio range you would be fine at that bore size with 3 to 3-1/2 inches of pedal travel. The 7/8 inch bore master will give you 30% more line pressure than the 1 inch, but 30% more travel. The 15/16 would be a good compromise if you don't like the travel, but the 7/8 would be your best bet.
     
  11. bigalturk1
    Joined: Sep 23, 2010
    Posts: 369

    bigalturk1
    Member

    Thanks for your opinions....

    >Yes, I did bench bleed the Master Cylinder
    >Yes, I did bleed the system properly
    >Yes, The F&R m/c reservoirs are the same capacity (75' Chevy Monza m/c)
    >Yes, The Rear brakes are adjusted correctly and hardly worn (Originals since assembled).
    >Yes, The Proportioning valve is all the way open
    >Yes, I may buy a 15/16" m/c... what application should I use?
    >No, I don't really want a Booster, besides all my plumbing is around the Master cyl. (No room).
    >No, I cut the pedal is a little shorter when I built the car...which does give me a different pedal ratio.
    >>>>>Does anyone want to sell me a stock 39' brake pedal?<<<<<
     
  12. You are running out of master cylinder piston volume.
    Go to a bigger bore and use power brakes for your wife.
    A longer pedal ratio with a larger bore master cylinder may work if
    you don't want to use a booster.
     

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