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Brake pedal ratio

Discussion in 'The Hokey Ass Message Board' started by Oldbill51, Jul 6, 2012.

  1. Oldbill51
    Joined: Jun 12, 2011
    Posts: 284

    Oldbill51
    Member

    Any one got a good suggestion on how I can increase my pedal ratio without totally screwing my paint on the frame here? Maybe some kind of bolt on bellcrank?

    Any help would be much appreciated, Bill

    Sent from my DROIDX using Tapatalk 2
     

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  2. XXL__
    Joined: Dec 28, 2009
    Posts: 2,051

    XXL__
    Member

    Move the pivot collar on the arm (??)
     
  3. roundvalley
    Joined: Apr 10, 2005
    Posts: 1,774

    roundvalley
    Member

    The ratio is on the brake arm. The foot arm pad has to be further away from the pivot or the rod arm needs to be shorter. Foot arm pad higher or rod arm shorter. These shoudn't affect the frame.
     
  4. squirrel
    Joined: Sep 23, 2004
    Posts: 50,283

    squirrel
    Member

    You need to move the pivot down on the frame, as well as on the arm. Fortunately it's on a place on the frame where it's pretty hard to see once you put the body on.
     

  5. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    mustang6147
    Member
    from Kent, Ohio

    There is a company that makes them. I forgot the name, but its called a "bell crank system" I think ECI sells there version, but this other company has a simplified version.

    It has a mounting point on the frame, then sleeved and the peddle shaft mounts to the top, and then the lower bracket is sized depending on how many time you want to increase the movement.


    I put it on my old 41, when I went to a vette master cylincer from the old single resivoir...... Its basically a mechanical multipier, and the pictures are on the website.

    http://ecihotrodbrakes.com/firewall_mounted_systems.html
     
    Last edited: Jul 6, 2012
  6. Oldbill51
    Joined: Jun 12, 2011
    Posts: 284

    Oldbill51
    Member

    I should have provided more information. The pedal arm fits the hole in the cab the way it is now, so adding length to that would result in the hole having to move in the firewall and intruding into the steering colume provisions and assembly, and screw that paint as well. If I shorten the rod arm very much it will begin to contact the botom of the
    k-memeber , and before it will improve the situation enough, it will actually intrude into the k-memebr itself. This would also require the master cylinder support bracket to be raised about the same amount. I hoping that someone else had encountered a similar situation and came up with some kind of inovative solution.

    Thanks again for all help,
    Bill
     
  7. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,474

    landseaandair
    Member
    from phoenix

    Like squirrel said, just remake the pedal and K member mount with the pivot further down and touch up the paint. Keep it simple.
     
  8. VoodooTwin
    Joined: Jul 13, 2011
    Posts: 3,455

    VoodooTwin
    Member
    from Noo Yawk

    The lower leg of the brake pedal needs to be longer to achieve more throw. But that'll mess with the plunger rod angle worse than it is now. So yeah, a bell-crank with unequal length arms would work. But man that's adding complexity to what should be a simple (and safe) setup.
     
  9. JohnEvans
    Joined: Apr 13, 2008
    Posts: 4,883

    JohnEvans
    Member
    from Phoenix AZ

    Wrong ! to increase the pedal ratio the lower arm needs to be shorter.
     
  10. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,789

    V8 Bob
    ALLIANCE MEMBER


    It might be the picture, but does the push rod enter the master at angles? Normally the push rod would be somewhere between the top and bottom of that frame K member, going through instead of under. You really don't want brake linkage to be in harms way, and running under the K puts it at risk.

    One possibility is to make the pedal shaft "live", with the much shorter lower arm now located inside the frame, sorta like the '39 Ford clutch pedal setup. The m/c bracket may have to be modified for a clear straight input from the arm.

    You want a 6-7:1 ratio minimum with most manual setups. :)
     
    Last edited: Jul 6, 2012
  11. railroad
    Joined: Feb 3, 2010
    Posts: 242

    railroad
    Member

    The master cyl push rod does not seem to be in line with the master cyl, so I am concluding you have a bell crank or another pivot arm making the final push into the master cyl. If this is true you can change the ratio on it and not mod your pedal/arm/ pivot. One more good picture, maybe from the bottom showing how the rod goes into the master cyl and I am sure you will get a workable solution.
     
  12. VoodooTwin
    Joined: Jul 13, 2011
    Posts: 3,455

    VoodooTwin
    Member
    from Noo Yawk

    I may have incorrectly assumed that he wants to INCREASE the throw of the master-cylinder push-rod. If he wants to decrease it, then I agree.

    It would help to know WHY he wants to increase his pedal ratio. Too stiff a pedal feel?
     
  13. Beanscoot
    Joined: May 14, 2008
    Posts: 2,205

    Beanscoot
    Member

    Changing the bore size of the master cylinder will achieve the same result.

    Going to a smaller bore MC will make it easier to apply the brakes.
     
  14. Oldbill51
    Joined: Jun 12, 2011
    Posts: 284

    Oldbill51
    Member

    Well it wasn't exactly easy but I think I have found a solution. Thanks to all for your input.
    Bill

    Sent from my DROIDX using Tapatalk 2
     

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  15. Oldbill51
    Joined: Jun 12, 2011
    Posts: 284

    Oldbill51
    Member

    Second picture didn't take for some reason. Again thanks.

    Sent from my DROIDX using Tapatalk 2
     

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  16. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,474

    landseaandair
    Member
    from phoenix

    Doubt you changed the ratio any, just the configuration.
     
  17. JohnEvans
    Joined: Apr 13, 2008
    Posts: 4,883

    JohnEvans
    Member
    from Phoenix AZ

    Well it won't win engineer of the year award ,but looks functional. One suggestion though ,your link would work better if there was another piece of metal on the open side of the Himes. No twist that way in the link, or change to clevis yokes.
     
  18. Look at the picture. The new pivoting bracket is changing the ratio quite a bit. The closer that the existing Heim joint is raised up to the rod that the pivot arm is the more ratio he will have.
    Good solution!!!
     
  19. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,474

    landseaandair
    Member
    from phoenix

    Did you see both pics? He gained leverage shortening the lower pedal arm but lost it again with the rocker assembly. It would work if the pedal rod and master cylinder push rod were both on the same bolt. They should probably end up one behind the other to avoid twisting though and the lower pedal arm should start at more of a foreward angle for a better mechanical advantage (very Rube Goldberg if you ask me). I'd just keep it clean and maybe move the master up or the pedal down myself. Either, way the lower arm on the pedal should still angle slightly foreward from the start.
     
  20. I see that now. As long as it clears everything and he has the throw good, then he succeeds. Hope this is the case. At least the rod that goes into the master is pretty straight now.
     
  21. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    Screw worrying about the paint on your frame, that won't kill you, a badly engineered brake setup will. You really need to get that thing so that the pushrod from the pedal makes a straight transition into the MC with none of that Rube Goldberg stuff in between. If you need to cut stuff up and start over sometimes that is the right way to do things. The frrame can be touched up after you make this thing right.

    What exactly is this thing pointed out by the red arrow ? If it is a bellcrank you lost every bit of mechanical advantage you thought you gained from the original setup.

    [​IMG]

    Don

    I just read Landseaandair's post and he is 100% on the money.
     
    Last edited: Jul 9, 2012
  22. unkledaddy
    Joined: Jul 21, 2006
    Posts: 2,865

    unkledaddy
    Member

    I agree with skipping the Rube Goldberg stuff!
     
  23. oj
    Joined: Jul 27, 2008
    Posts: 6,281

    oj
    Member

    I don't think you will get enough movement thru the pedal to operate the 2nd piece and drive it deep enough into the master cyl to get any kind of brake pressure.
    It is time to get out the sawzall, the welder, some raw materials and redo the whole mess. You can get a can of matching touchup paint.
     
  24. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    I guess the question that needs asking is, what company made that pedal and mc mount assembly, and what was it supposed to fit ? With the nice way it was mounted and everything detailed it is obvious the owner put some hard work into the frame. The pedal looks like a professionally made piece, so it must have been made for some application, and just wondering why it fits this setup so badly.

    Don
     
  25. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    I changed one of the original photos he posted so that it was easier to see what he has, and it looks like the original pedal setup was altered to make it fit. There is an added on section to drop it down lower and it is using back to back rod ends, which is kind of bizarre. I think that is what is causing this problem, he has reworked it to a shape that it wasn't intended for and ended up with about a 3 to 1 ratio instead of the 6 or 7 to 1 he should have.

    Don

    [​IMG]

    I've looked at his picture above a little more and I think I see what has happened here. The pedal assembly was probably made to use with an X or K member that wasn't cut the way his is cut for transmission clearance. It was designed for the MC to sit more directly behind the pedal and it would have been ok in that position. BUT, since his crossmember is cut out there the MC is way off to the drivers side and he had to add on the piece indicated by the red arrow to kick the rod over to line up with the pedal.

    Not sure how you are going to do it, but you need to redesign that setup so the original ratio is restored and the pushrod is going straight back into the MC, not through that bellcank you have made.
     
    Last edited: Jul 9, 2012
  26. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    I think I have a fix for Bill, but he may not like this option. I would totally forget about using the underfloor setup and buy one of the 180 or 90 degree setups sold by Kugel Komponents and put the whole thing under the dash as a swing pedal assembly. My Son used one in his rpu and I am using one in my rpu project, It really is a clean setup and works great.

    Just a thought. Here is a link to kugel and their products:

    Don

    http://www.kugelkomponents.com/zencart/index.php?main_page=index&cPath=4

    He has such a misalignment issue between the bottom of the pedal and the spot where the pushrod enters the MC that I really don't know if he could kick either or both of them enough to close that gap.

    [​IMG]
     
    Last edited: Jul 9, 2012
  27. If you bleed the brakes and you have a hard pedal (That doesnt go to the floor) and then you take a slow drive, stab the brakes and see how it feels then you can raise or lower the fulcrum point up or down a bit to create the right force.
    There is no way you will push the rod through the master cylinder with too much force. This would take incredible force to blow seals etc and if that were the case, people with real strong legs would be losing their brakes all the time. People are making this too difficult and no it's not a safety issue until failure which would be in bad welds, pedal hitting the floor before brake pressure etc.
    Bleed the brakes , get a solid pedal, go for a small drive , come back and adjust as needed. It's hydraulics, not rocket science. Think about how alot of people don't use a dual master cylinder. A small leak in one seal and game over!! That is unsafe as far as I'm concerned and millions of cars were built this way. If half these guys on this board were trying to design a hydraulic brake system, they would freak out that there is only one seal on each wheel cylinder and say that they are unsafe yet thats all there is on most every brake. One cup or o-ring!!!!!!!
     
  28. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,789

    V8 Bob
    ALLIANCE MEMBER


    Your previous post #25 stated the plunger went through the master cylinder, (almost an impossibility!) and said nothing about a booster. :)

    Generally, a 10 or 12 to one pedal ratio will result in the pedal hitting the floor/firewall well before the master or booster ever get near full travel, much less doing any damage to either.

    Not sure how you determained the diaphragm pushed through the seal, as it's travel is limited by the booster can and master cylinder.

    When DOT FMVSS 105 (all US cars/lt trucks) was manditory, (up to about 2005) one part of the test was a "spike" test, where the pedal force (manual or boosted) had to hit/exceed 200 lbs, from 30 MPH, and in .08 seconds. Now, muliply that 200 lbs by the nominal pedal ratio of 3:1 power/6:1 manual, and the resulting booster or master push rod forces were 600-1200 lbs!
    I've tried, but do not EVER remember a booster diaphragm or master cylinder failure in the hundreds I performed. (LOTS of other carnage! :eek::D)

    You're right-pedal ratio is very important! :D
     
    Last edited: Jul 9, 2012
  29. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,474

    landseaandair
    Member
    from phoenix

    I'm guessing by the last couple of posts, there's been at least one post removed from this thread? Anyways, Don's Hot Rods saw a couple things I missed like the offset issue and double heims??? Best probably to start from scratch, whether under floor or dash. If the owner is stubborn enough to stick with what he's got, that initial angle of the lower arm on the pedal is going to move up as much as back through its range of motion. It could end up inline or even off center and possibly lock the brakes with no return. I'm not one to cry about a single or fruit jar master cylinder but that arrangement is far from ready to run and needs to be sorted before it sees the road.
     
  30. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    There may be another way to solve it and still keep the underfloor pedal. If you tuck the MC closer to the inside of that crossmember by remaking it's mounting bracket you can move it closer to the center of the car. Then, if you take a cut off wheel and carefully remove the mount that holds the pedal in place you could move it further up that crossmember to a spot where it puts the arm of the pedal more in line with the center of the MC. (As you move it further up that crossmember it will naturally move more to the left)

    By moving the MC to the right and moving the pedal to the left you could get close to having the pushrod be a straight shot. If you were still off it wouldn't be a sin to put a little longer pivot bolt and spacer on the pedal arm to shove the rod end even more to the left.

    Once you had everything lined up you would have the ratio you want and the pushrod would not be on an angle. All that would be needed then might be to reshape the top part of the pedal to move it left or right to where it goes around the steering column and fits where you want your foot to be. I think a days work could get this thing corrected and the car would be safe.

    Don
     

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