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Technical '39 Ford Dual Master cylinder low pedal help please...

Discussion in 'The Hokey Ass Message Board' started by Tim G, Nov 9, 2016.

  1. Tim G
    Joined: Jan 3, 2009
    Posts: 548

    Tim G
    Member

    I converted a customers '39 Ford sedan(with original drum brakes) to dual master cylinder using a Land Rover master cylinder. I had previously done this on my '40 Chevy Coupe and it worked out great. However the pedal was low, with no air in the system and the brakes adjusted a little too tight for my liking it was still low. the brakes worked fine but it didn't inspire confidence.

    So, I had the car back in, ordered a master cylinder(Mustang I believe) and adapter from honest Charley's and fitted that instead. It is exactly the same! It is a 15/16" master cylinder( http://www.honestcharley.com/dual-master-cylinder-for-manual-shift.html) with 4 outlets, I had to blank two as they come out right against the exhaust. I did have to use 3/16" brake lines because the outlets are 3/8" and that's too small to run 1/4 right(?), could that really make that much difference?

    Anyone had a similar problem to this?

    Thanks
     
  2. manyolcars
    Joined: Mar 30, 2001
    Posts: 8,391

    manyolcars

    It seems that brake problems are the most common. Wouldnt it be nice to have a dedicated section only for brakes? or an index
     
    Tim G likes this.
  3. hotrod37
    Joined: Aug 8, 2006
    Posts: 116

    hotrod37
    Member
    from Indiana

    Stock 39 Ford master is 1.06" bore. You are using a smaller bore master. Pressure will be lower and more fluid out of master to fill the wheel cylinders.
    Find a Mustang will 1" bore or same size as old one. Bigger will give more pressure and less movement. Maybe find a 1 1/8" bore.
     
    Tim G likes this.
  4. Tim G
    Joined: Jan 3, 2009
    Posts: 548

    Tim G
    Member

    Well, we have a search facility and there are threads about fitting dual circuits on these brakes but I couldn't find anything relating to lack of pedal...
     

  5. Tim G
    Joined: Jan 3, 2009
    Posts: 548

    Tim G
    Member

    It's not that easy just to find another master cylinder here in the UK, I told the guys at Honest Charley what brakes we were running and they told me this was the master cylinder for the job, It worked out very expensive by the time it was shipped, taxes paid etc. Are they not a reputable company that should know what they are selling? I Assumed they were...
     
  6. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,714

    V8 Bob
    ALLIANCE MEMBER

    The result of using a smaller bore master is higher output pressure for a given pedal force input, but at the expense of longer pedal travel. The big problem is probable loss of full master cylinder stroke with the '39 pedals, which eliminates the safety advantage of a dual master. I would not go any smaller than a 1" bore, but still making sure the master can be fully stroked before the pedal bottoms out.
    The use of 3/16" lines should not be a problem, but residual valves, factory internal or aftermarket 10 # external, are needed for those vintage drum brakes.
     
    Last edited: Nov 9, 2016
    Tim G likes this.
  7. If you're running drum/drum, the 67 and 68 mustang master cylinder drum/drum set up should work and be 1". I know on my F-1 I had to adjust my pedal after installation by turning that little sprocket looking thing on the pushrod. Do you have this adjustment?
     
    Tim G likes this.
  8. Since you asked, my opinion is "NO". When you get a bunch of separate buckets it takes longer to navigate the site if you intend to read everything. People tend to only go where they are interested. This means that people who may have the answer will never read the question. If the choice was mine, I would leave things as they are. The "index" is called "the search function".

    Charlie Stephens
     
  9. neilswheels
    Joined: Aug 26, 2006
    Posts: 856

    neilswheels
    Member
    from England

    I saw a thread on this recently, the conclusion was use a vette non power MC, as the bore is bigger than a Stang, and this sorts it. I'll see if I can find the thread
     
    Tim G likes this.
  10. neilswheels
    Joined: Aug 26, 2006
    Posts: 856

    neilswheels
    Member
    from England

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  11. squigy
    Joined: Nov 30, 2003
    Posts: 3,915

    squigy
    Member
    from SO.FLO.

    Are the drums adjusted properly? Thats where i would have started.

    Sent from my SM-G900T using The H.A.M.B. mobile app
     
  12. Tim G
    Joined: Jan 3, 2009
    Posts: 548

    Tim G
    Member

    Yes, As I stated in my first post.
     
  13. Tim G
    Joined: Jan 3, 2009
    Posts: 548

    Tim G
    Member

  14. Automotive Stud
    Joined: Sep 26, 2004
    Posts: 4,155

    Automotive Stud
    Member

    Just curious, are you running a proportioning valve?
     
  15. Tim G
    Joined: Jan 3, 2009
    Posts: 548

    Tim G
    Member

    Yes, Adjustable.
     
  16. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,714

    V8 Bob
    ALLIANCE MEMBER

    Why a prop valve?
     
  17. Tim G
    Joined: Jan 3, 2009
    Posts: 548

    Tim G
    Member

    We put it on because we didn't know if there would be too much pressure going to the rears. It is currently set to give no resistance.
     
  18. A 1-1/8" master cylinder will require more pedal pressure than the original 1-1/16"
    bore.
    Mart came up with a 1-1/16" dual master of a E-250 Econoline that addressed the low pedal problem he was having with the commonly used 1" bore Mustang master. I also found that the larger bore addresses the problem of the pedal "bottoming" out against the floor when in failure mode (simulated while bleeding). This relates to using the original pedal assemblies; maybe aftermarket pedal assemblies have a lower ratio to address this. One drawback is that it is physically larger.
    I believe that 1/4" lines work better with the high volume early Ford Lockheed brakes. While the final applied pressure would be equal with 3/16" lines; the 1/4" flow better during application and release. Pretty sure Henry's engineers got it right back in '39. Just saying.
     
    Tim G likes this.
  19. birdman1
    Joined: Dec 6, 2012
    Posts: 1,067

    birdman1
    Member

    keep in mind drum brake shoes travel farther than disc brakes . takes more volume of fluid. that means a bigger piston in the master to get the required volume.
     
    Tim G likes this.

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