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model a hydraulic brake problems?

Discussion in 'The Hokey Ass Message Board' started by captain j, Mar 16, 2013.

  1. DICK SPADARO
    Joined: Jun 6, 2005
    Posts: 1,887

    DICK SPADARO
    Member Emeritus

    You cannot have a hard pedal and no brakes unless you are bottoming out the master cylinder piston. If you are bottoming out the master cylinder then you dont have enough piston fluid displacement, wheel cylinders expand and then stop because there is no more fluid to displace the wheel cylinders.. Master cylinder displacement too small. Doesnt matter what the pedal ratio is.
     
  2. gimpyshotrods
    Joined: May 20, 2009
    Posts: 18,031

    gimpyshotrods
    ALLIANCE MEMBER

    It does sound like more than one problem. If his measurements are correct, he's got a 2:1 pedal ratio.
     
  3. When I did mine, I used a mid 60's Mustang non power/drum MC. I also shortened the arm pushing the plunger into the M/C quite a bit shorter then the arm coming from the pedal to the brake shaft. I also used Residual valves. All worked handy/dandy
     
  4. captain j
    Joined: Dec 21, 2008
    Posts: 125

    captain j
    Member

    I can only get about 1 inch of pedal travel before it stops. So I would assume the mc is only going half way in then. If 2 inches of pedal equals 1 inch of push rod into the mc. That means for some reason the mc is only going in a half inch then stopping. That's using a pretty firm foot pedal push.
     
  5. captain j
    Joined: Dec 21, 2008
    Posts: 125

    captain j
    Member

    a few pics of what it looks like
     

    Attached Files:

  6. captain j
    Joined: Dec 21, 2008
    Posts: 125

    captain j
    Member

    a few more
     

    Attached Files:

  7. Mart
    Joined: Mar 3, 2001
    Posts: 4,378

    Mart
    Member

    Sorry my friend, but the ratio's are all f'd up

    The big fabricated lever that the pull rod pulls on is mounted down the dip of the cross shaft. You have to project a straight line between the pivot points and then see how far the lever sticks up from that line. The effective length of that lever is very short.

    You need to work out the leverages at each point. First the pedal. Distance from the pad to the pivot and distance from the pivot to the rod attachment point That is your first ratio. for the sake of argument lets say the pedal is 9" long and the lever is 3" long, that is a 3:1 ratio. (You can insert the correct figures).

    Then the distance from the projected pivot point of the cross bar up to the attachment of the new lever that's about 2". Then the same for the push rod attachment point on the pusher lever lets say 4". That's a 2:1 ratio the wrong way. So if the measurements are right, you have a ratio of 1.5:1 No good at all.

    The new lever on the cross shaft has to be a lot longer. Also the end needs to be vertical so it is in the same plane as the boss on the pedal. There also seems to be a lot of alignment issues and things rubbing. The attachment of the pull rod to the fabricated lever looks ill thought out too.

    Sorry to be so critical but it is a safety critical item and should only be done one way - the correct way.

    Come back with some accurate measurements and we can see what you have.

    Mart.
     
  8. budd
    Joined: Oct 31, 2006
    Posts: 3,478

    budd
    Member

    so on my stock A if i move the pedal 6" the rod moves 1-1/2", 4 to 1
     
  9. budd
    Joined: Oct 31, 2006
    Posts: 3,478

    budd
    Member

    have you made any progress?
     
  10. captain j
    Joined: Dec 21, 2008
    Posts: 125

    captain j
    Member

    Yes, I pulled the cross shaft rod out yesterday and welded up a new attachment point on the driver side so that the pivot point was not down on the bend. On the passenger side I drilled a hole for the pin about half way down that arm. I'll now use one shaft directly from that point to the master cylinder and its going into the m/c a lot straighter. Have to make that rod today after work. I measured the attachment pin on the driver side is two inches high and the pass side is 1.5 inches high from the centerline of the cross shaft pivot. The driver side was lower before and the pass side was like 4 inches high
     
  11. Mart
    Joined: Mar 3, 2001
    Posts: 4,378

    Mart
    Member

    Good. It all sounds like you are moving in the right direction.

    Mart.
     
  12. captain j
    Joined: Dec 21, 2008
    Posts: 125

    captain j
    Member

    I just measured the pedal height and height of the pedal pushrod from centerline of pivot. Pedal approx 12 inches high. Pushrod off of pedal approx 3 inches high.
     
  13. Mart
    Joined: Mar 3, 2001
    Posts: 4,378

    Mart
    Member

    So around 4:1 on the pedal. you want about 1.25 to 1.5 :1 on the cross shaft to net between 5:1 and 6:1 overall.

    Should work well then.

    Mart.

    Edit: Just re-read your note on the crossshaft mods and you have a 1.33:1 ratio there so 4 times 1.33 is 5.33:1 - pretty good.

    M.
     
  14. Kensey
    Joined: Sep 25, 2006
    Posts: 737

    Kensey
    Member
    from Pittsburgh

    I'd get a good heat shield between the m/c and the muffler.
     
  15. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,750

    V8 Bob
    ALLIANCE MEMBER

    caption j,
    You really need to reevaluate your brake pedal linkage, as it leaves a lot to be desired. There are much less complicated (and ratio correct) conversions that keep the master cylinder on the left side with the battery in place, but why not move the battery, as your Model A is hardly stock with that late drive train, and then have plenty of room to mount the master cylinder behind the pedal with direct linkage without bell cranks?
    You may want to modify the park brake cable attachment as well, such as replacing the present cable bolt with a short metal tube, or OE style equalizer.
    The brake system is a very important part of the vehicle, and needs be designed and built as safely as possible. Hopefully my comments/criticism will be taken constructively, as intended. :)
     
  16. captain j
    Joined: Dec 21, 2008
    Posts: 125

    captain j
    Member


    I would rather of had the mc on the driver side. I would've just moved the batt no problem. The problem is when you push the pedal it pulls the rod to the front of the car which in return I would still have to fab up some push/pull levers. The whole big cross shaft came in the ( t-5 trans to stock 4 banger engine) adapter kit. Just using what was there. Obviously it's not ideal but will work and is def heavy duty solid bar. I'm asking you guys on here for help because I do want the car to be safe. I still have some rod clearance to take care of among other stuff. I do have a brake line equalizer that will go on it. Just did what I did on the e brake for my front of house test runs w the regular brakes. It's not permanent. I do appreciate everyone's input.
     
  17. budd
    Joined: Oct 31, 2006
    Posts: 3,478

    budd
    Member

  18. captain j
    Joined: Dec 21, 2008
    Posts: 125

    captain j
    Member

    We definitely made progress! I now have more than an inch of pedal travel, it about goes to the floor. So now I know the master cylinder rod is moving more than a half inch also. The pedal is pretty soft now compared to before. I may have to rebleed the brakes now that its working correctly. I engaged the pedal and put a board on it and the wheels are pretty stiff compared to before I could still turn them. I'll make some final adjustments and take it for a test spin later next week. The linkage and pedal ratio makes a difference. I never knew how much of a difference the crossrod and linkages made compared to how high they were mounted.
     
  19. captain j
    Joined: Dec 21, 2008
    Posts: 125

    captain j
    Member

    That is a nice set up. I'd have to cut a hole underneath the seat to access the reservoirs. Maybe next time ill do his idea!
     
  20. captain j
    Joined: Dec 21, 2008
    Posts: 125

    captain j
    Member

    Update, I still had weak brakes after all this along with a soft pedal going to the floor. After researching a little I found out the original 46 ford deluxe master cylinder was an 1 1/8 inch bore. The new one I put on was an 1 inch bore so I basically wasn't pushing enough brake fluid to the wheel cylinders. I put the original 46 ford m/c back on and now the brakes seemed to stop the car pulling in and out of the garage. Ill try to get it out for a road test this Friday and see how she stops.
     
  21. DICK SPADARO
    Joined: Jun 6, 2005
    Posts: 1,887

    DICK SPADARO
    Member Emeritus

    I think I told you that 10 days ago in post # 31. Now follow instructions on getting your pedal ratios squared away and you will be doing donut stops.
     
  22. captain j
    Joined: Dec 21, 2008
    Posts: 125

    captain j
    Member

    I understand what you were saying, I had the same issue with 46 master cylinder in there in the first place. My main problem was the linkage and pedal ratio. I tried to make it better by changing the M/C but in fact made it worse with the smaller bore. Now I was up against two problems which were both my fault. Once i got the linkage n pedal ratio figured out i now could attack the lack of fluid displacement. Without everyone's and your knowledge I don't think I would've figured it all out. Thanks
     

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