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Terrible floor mount brake pedal

Discussion in 'The Hokey Ass Message Board' started by Probesport, Jan 6, 2012.

  1. Just finished up the brake pedal assembly for the A I am working on, not as fancy as some of the ones you guys have built but it works well for me.

    It was built so that everything will disassemble easily for maintenance. The main body is made from 1/4" plate, the pivot rod is 3/8" and the actual arm/lever is a GM steering arm. I still need to work in a return spring and a stop but I will probably mount everything before that.

    [​IMG]

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    I'm glad to be moving on this car again, the past year or so has been crazy for me and I haven't had much of a chance to get back on it.
     
    Last edited: Jan 6, 2012
  2. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,627

    V8 Bob
    ALLIANCE MEMBER

    Are you using a booster, as the pedal ratio looks too small for a manual system. Otherwise, nice job. :)
     
  3. No I'm not using a booster, I have an AMC manual disc/drum master but it seems to have full travel pretty quickly. It is real close to the master and just moving the bracket allows me to change the relationship - until its welded on of course.
     
  4. Ole don
    Joined: Dec 16, 2005
    Posts: 2,915

    Ole don
    Member

    That looks plenty stout. I have seen the aftermarket flame cut 3/8 metal pedals bend under a panic stop. I like the old Ford forged steel pedals. I have some if anyone needs them.
     
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  5. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,627

    V8 Bob
    ALLIANCE MEMBER


    The reason full travel comes quickly may be because your ratio is too high, and will result in very high pedal force during braking. You want close to 6:1 ratio for most manual systems, and 3:1 for power. What is your ratio?
     
  6. I don't have the real ratio yet as it's permanent home doesn't exist yet. I can get close with the planned setup but I don't have the measurements to do the calculation on hand but have been basing it on around 5:1

    Quickly may be subjective as well as it's not mounted to the floor frame yet. It's similar to the prefab assy i took out of my old t-bucket which had a decent setup so that was my starting point.
     
  7. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,627

    V8 Bob
    ALLIANCE MEMBER

    The ratio is determined by the pedal pivot to push rod distance divided into the overall pedal length, not the placement or location of the assembly.
     
  8. Correct, however depending on where the mount is that relationship changes.

    If I mount the assemble closer or further away from the master the distance of those 2 points will change. This arm isn't exactly a straight line and I am using the angle of the arm to my advantage.
     
  9. Scarebird
    Joined: Sep 26, 2006
    Posts: 860

    Scarebird
    Alliance Vendor
    from ABQ, USA

    Not true. Your lever is converting the force to lineal motion - nothing else. Unless you have a reducing bellcrank this will not work. Note the ratios in the attached pic... using a GM steeringarm will not give you the ratio previously stated needed for proper braking.

    edit: unless you mount the master at the 5 o'clock position, making the force less tangential, but you cannot do that due to room and bleed constraints.
     

    Attached Files:

    Last edited: Jan 6, 2012
  10. Seriously doubt that you would be able to generate adequate braking pressure with that pedal, you need to increase the ratio of the pedal itself. The location of the master cylinder does not change the ratio.
     
  11. Thanks for the info guys, I'll be scrapping the assembly tonight when I get home and move on to another area of the project. It's exactly what I wanted but if it's not going to work then it's not going to work, I will post the glorious demise this weekend.

    The only proper way to destroy something you've been working on awhile is with explosives, and I think I have the proper amount for this little thing here.... :)
     
  12. pasadenahotrod
    Joined: Feb 13, 2007
    Posts: 11,776

    pasadenahotrod
    Member
    from Texas

    Don't be silly! Just extend the top part of the pedal arm above the pivot point or the lower end gets shortened or a combo of the two just enough to get the ratio you need. Judging by the pics your pedal ratio is just under 2:1 now. It needs to be at 3X longer on the top end and you're there. No biggie.
     
  13. hot_rod_bones
    Joined: Sep 25, 2011
    Posts: 195

    hot_rod_bones
    Member
    from topeka, ks

    hey now, dont discourage the man.......


    from blowing stuff up.

    i for one learned something from his mistake, im glad he posted it. you guys saved his life and his ride.
     
  14. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    We all have bins of stuff we scrapped that we thought would work, it is just part of the game. :D The guys are right, you couldn't have exerted enough pressure on that one to stop it, but once you make one with more length on the part that is above the pivot point you will be fine. 6 to 1 or 7 to 1 is ideal.

    Don
     
  15. 201
    Joined: Dec 17, 2002
    Posts: 344

    201
    Member

    What Dons hot rod said!! If you look at say the Comp. Eng. after market petals, frome the pivit to where the petal pad goes, it's 14 in. From the pivit to where the clevis/m/c rod hooks up, its 2 in, so it's 7 to 1 ratio.
     
  16. I'm not sure about saving my life, it was fairly easy to push and it's not the first time I've randomly built a brake pedal assembly for me but I plan on keeping this car some time and eventually I wont be thirty-something anymore.

    If I go much longer at the top my foot would get stuck and moving the pivot down is also not an option. To keep this assembly in any way, shape or form it would require changing a bulk of the floor/frame/MC/cowl, etc. Making it 3x longer at the top puts it into the dashboard.

    This was really the best solution for the scenario and if it doesn't work then the scenario has to be changed. Scrap with extreme prejudice.

    The plan is for complete destruction amonitrate style, just need to make sure our blast hole is clear and still intact.
     
  17. There are at least a few ways to increase the leverage.
    Add a 2:1 or 3:1 bell crank. That will double or triple the existing pedal ratio and keep pedal travel short if you have space issues.
    Shorten the rod end, lengthen the pad end.

    A lot if this depends on how much pedal travel you have available to use.

    Drawing it up full size helps. Making a live model out of cardboard helps visualize this.
     
  18. need louvers ?
    Joined: Nov 20, 2008
    Posts: 12,911

    need louvers ?
    Member

    Don't feel bad man, Sometime I think my scrap it bin is bigger than my go out the door bin!
     
  19. I don't feel bad at all, I don't do the same thign twice however so if I cant do it the way I want it it gets destroyed. I stopped keeping a scrap bin as I just kept stockpiling stuff.

    The bellcrank option may be possible in the space I have, Pedal travel is not a big concern, its height and depth due to the chop/channel that gets tricky. I can move the center pivot without too many issues or ill effects.

    I may have to see what I come up on that end before I go and make metal soup.
     
  20. Mine get Hung on the wall. Most of them look pretty cool, just didn't work or fit,
    Sometimes you find another use for it later down the road,
     
  21. I thought you might have room and that could be an option because you said nothing was mounted yet and by how long that rod was. Too high of a pedal can be an enormous drag on driving. Not enough travel leaves you without brakes or a pedal so hard you bust the seat mounts.

    Bent arms can do an awful lot with leveage and ratios as well as travel vs throw directions.
     
  22. I will be nearly sitting on the floor, after seat frame and padding only about 6-8 inches up and the back will be on the rear frame "Z".

    I had never considered the bellcrank option but sketching it out in my mind I have should have the space under the floor for it.
     
  23. So it's a bit better, I haven't destroyed anything yet as I was able to make some clearance moving up the dash and scooting the steering wheel location slightly. This should put me just under 6:1

    [​IMG]

    Although not ideal per some of the recommendations, it should suffice just fine. I still have to clean, smooth and paint everything but I think this is a workable solution.
     
  24. Reggie
    Joined: Aug 25, 2003
    Posts: 1,700

    Reggie
    ALLIANCE MEMBER

    The 3/8" pivot pin would also worry me. I personally would not use less than a 5/8" pivot.
     
  25. Don's Hot Rods
    Joined: Oct 7, 2005
    Posts: 8,319

    Don's Hot Rods
    Member
    from florida

    That looks better. Proper brake pedal positioning is super important. I've driven hot rods where the builder squeezed in the pedal due to space limitations and they were awkward to drive. In a panic situation you want your brake pedal to be right where your left foot expects it to be.

    Another thing that makes or breaks a brake pedal is where the pedal pad hits your foot. You want it to hit just above the arch and just below your toes, in that padded part of the foot. It is not only more comfortable there but you get maximum push with that portion of the foot. If you reach down and grab your foot you will feel the part I am talking about, or just look at your daily driver and where you rest your foot on that pedal. The factory engineers design the pedals to hit you right there.

    Don

    PS, I agree with Reggie, use a 5/8 bolt for the pivot.
     

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