Brake Pedal Ratios

Chassis, Suspension and wheels

  1. Duke5A

    Duke5A Well-Known Member

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    Is there any difference in the pedal ratio between power and manual brake cars? I've seen F body cars with factory manual brakes.

    Thanks!
     
  2. Oldiron440

    Oldiron440 Well-Known Member

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    Yep, I've got one, no power steering as well.
     
  3. Duke5A

    Duke5A Well-Known Member

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    Is the pedal longer? Everything I read it looks like the common ratio for manual brake cars is 7:1. The power pedals are 4.5:1.
     
  4. XfbodyX

    XfbodyX Well-Known Member

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    Your not using the pin and clevis from the power setup are you?
     
    Last edited: Feb 9, 2020
  5. Duke5A

    Duke5A Well-Known Member

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    If I can get away with it. Is it more of a difference than just the pedal?
     
  6. XfbodyX

    XfbodyX Well-Known Member

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    The manual setup does not use it.

    Not sure if I can do it tonight but I will post some pics.
     
  7. Duke5A

    Duke5A Well-Known Member

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    That would be awesome, but don't worry about posting tonight. I'm sourcing parts for Spring time. Going to order what I still need off of Summit this week.
     
  8. XfbodyX

    XfbodyX Well-Known Member

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    The whole ratio deal kinda goes out window when you have so many non oem parts to your system. Ive two cars that use nothing oem from the mater out other then the oem hard line going to the rear.

    On this rig here, I had power brakes and tossed all the oem parts and have the WW 4 piston units up front and the older exp. discs on the rear but upgraded. Tried 3 diff MC units with different bore sizes.

    I just run the oem manual rod from the pedal (oem hole location) to the MC, didnt even need the adjustable rod.

    So I guess what im getting at it you might not want to stock up on too much as it my go easier then you think and its easy to order parts and have them in a couple days but every car is different.

    You can see in the first pic where the part in the second pic would go.

    1.JPG

    2.JPG

    3.JPG
     
  9. BudW

    BudW Moderator Staff Member

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    The manual and power brake "petals" are the same.

    The master cylinder pushrod is in a different location for power brakes vs. manual brakes.

    Power brakes add a multiplier to the pushrod, which also raises the pushrod (to booster) up about 1½”, or so.
    PB multiplier.JPG

    ’76 to ’77 (or maybe mid-year ’78) F/M-body will have a 4-bolt iron brake master cylinder. The lower 2 studs for manual brake master cylinder and lower 2 studs for brake booster share the same two lower firewall holes.
    ’78 (or mid-year ’78) to ’89 all use a 2-bolt aluminum master cylinder uses a different set of holes on the firewall.

    I think that power brake multiplier is tossing a wrench into your calculations (maybe).
    BudW
     
  10. Duke5A

    Duke5A Well-Known Member

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    Alright, if the pedals are the same do both setups have the same mechanical advantage? I didn't think this was going to be such a pain. :confused:

    Do I need to find a donor vehicle or do I just roll with what I got?
     
  11. 80mirada

    80mirada Well-Known Member

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    the power brakes use a linkage that isnt used for manual. You just hook the manual pushrod directly to the pedal, leave the linkage with the booster
     
  12. BudW

    BudW Moderator Staff Member

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    Edited for content.

    There is someone here looking for the booster force multiplier linkage (possibly). @Aspen400 . . .maybe.
    BudW