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Thread: Master cylinders

  1. #1
    Junior Member
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    Dec 2018
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    Master cylinders

    Sir
    During assembly of the peddle box on my gen 3 coupe it came to my attention that the master cylinders bore were different sizes. As per the instructions on page 180 the 3/4 Master cylinder goes into the left mount and the 5/8 master cylinder in the right mount. The picture illustrating this shows the master cylinders one on top of the other not left to right. Question 1. Which master cylinder goes in which slot. On Page 182 where it talks about balance bar adjustment it states the master cylinders are the same size bore. This contradiction in the manual is causing further confusion. I called factory five and was told it doesn't matter which size master cylinder goes in which position. I did not get an explanation as to why it doesn't matter.
    Question 2. Could anyone explain the thought process behind the two different size bore master cylinders. And The thought process behind why it now doesn't matter.
    Thank you
    Bill-53

  2. #2
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    The quick answer is this-

    Typically the coupe and roaster are a lot closer to 50/50 front/back weight balance that most anything you're going to use for donor brakes.

    Given this, Detroit engineers brake bias into front + rear caliper piston sizes (and pad sizes and rotor sizes, etc).

    So your typical Mustang front calipers do a lot more braking than Mustang rear caliper, by design (at equal MC pressures - typical OEM).

    Put these front + rear systems in a car that's 50/50 weight distribution and sprung like a go-kart (in some cases) - the fronts tend to lock early and the rears aren't effective.

    So the 5/8" MC is meant to plumb to the rear brakes (5/8" gives higher pressure), and the 3/4" MC plumbs to the front.

    It doesn't really matter much which side of the balance bar they are arranged - the balance bar lets you fine tune the pressure headed to the rear calipers vs the pressure headed to the front calipers (it adjusts in either direction).


    So it really doesn't matter left vs right - whatever is simpler to plumb properly.


    Clear as mud?
    Last edited by mike223; 02-12-2019 at 01:35 PM.

  3. #3
    Top Notch Builder P100DHG's Avatar
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    Must be invisible mud cause that was pretty clear. Wow big thanks for the question and amazing answer.

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