Register now to get rid of these ads!

Help Measuring Brake Pedal Ratio

Discussion in 'The Hokey Ass Message Board' started by 3spd, Jun 2, 2012.

  1. 3spd
    Joined: May 2, 2009
    Posts: 540

    3spd
    Member

    I want to put a reverse swing master cylinder under the dash of my 56 Buick. I have a 1" master cylinder and I am aiming for a 6:1 pedal ratio. I will also need 1.5" of push rod travel to bottom out my master cylinder. To do this and clear the firewall/floor I am going to have to make the pedal arm bent. How does one measure the pedal ratio on a bent pedal? I have attached a picture of a pedal I cut out of cardboard that will give the proper push rod travel, clear everything, and hopefully give me the correct pedal ratio.

    I figure the pedal ratio is 5.7:1, am I correct? The top hole is for the push rod yoke and the middle hole is for the pivot. To get the ratio I just measured the straight line distance from pivot hole to the end of the pedal (10") (will be the middle of the brake pedal pad) and divided it by the distance from the top hole to the pivot hole (1.75") giving me 5.7. Is this the correct way of measuring?

    Thanks,
    Ryland
     

    Attached Files:

  2. EDPACECAR
    Joined: Nov 25, 2006
    Posts: 74

    EDPACECAR
    Member

    Formula for Pedal Ratio:

    Pedal ratio is the ratio of leverage you brake pedal applies to the master cylinder. To determine the pedal ratio you need to measure the height of the pedal to the pivot point then divided the measurement of the pivot point to the lower arm that controls your rod to the master cylinder.

    A = height of pedal
    B = center to center measurement of the lower arm
    C = pedal ratio
    A divided by B equals C
    Or example 9" divided by 1.5" equal 6 to 1 ratio
     

    Attached Files:

  3. A Chopped Coupe
    Joined: Mar 2, 2004
    Posts: 1,133

    A Chopped Coupe
    Member

  4. Fenders
    Joined: Sep 8, 2007
    Posts: 3,922

    Fenders
    Member

    To answer your question directly:
    (1) I believe you are correct in calculating the ratio, and
    (2) I my opinion 6:1 is fine (FWIW)
     
    Register now to get rid of these ads!

  5. 3spd
    Joined: May 2, 2009
    Posts: 540

    3spd
    Member

    Correct me if I am wrong but how I am thinking about this is that it all comes down to torque, and boiled down torque is force times radius. It doesn't matter what the pedal does (if the pedal does not flex) in the end the radius from the point of force to the pivot is what matters. This also means that it does not matter if the push rod side and the pedal side are in line with each other because the are separate systems tied together by the central pivot. As long as the pivot is solid it will transfer the force equally.

    Thanks,
    Ryland
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2020 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.