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Thread: Brake Booster Pushrod Adjustment - Master Cylinder Swaps

  1. #1
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    Default Brake Booster Pushrod Adjustment - Master Cylinder Swaps

    We have gone over a variety of brake swaps on this site from the anemic 10" front disc setup to the less anemic 11" front brakes and then adding on the TC rear disc brake setup and finally to adding the pinnacle of all Fox calipers the SVO/Lincoln 73mm front calipers. We pretty much know that going from the 10" to 11" front brakes and if we are running the stock drum brakes in the rear a MC (13/16" bore) swap is not necessary as the piston size on the calipers is the same at 60mm. Now when we up the game to the TC rear brakes (45mm caliper) with the 60 mm front calipers we need to upgrade to a different MC (1" bore). It is really hard to find the MC piston size anywhere due to the Hydro-boost system and the Teves II crap but remember the 1993 Cobra had the same braking system so that is where you find the MC bore diameter for that setup since the Cobra and TC shared the same brakes. Now when we upgrade to the SVO/Lincoln Mark VII 73mm front calipers a yet a different MC (1-1/8" bore) is once again needed.

    This also applies when you install the SN95 V6/GT brakes on one of our cars. If you are installing the 94/95 GT or 94-98 V6 brakes they came factory with a 1-1/16" bore MC and the 99-2004 V6 cars came factory with a 1" bore MC. Just in case some folks do not know, in 1996 and up all of the GT and Cobra cars went to hydro-boost and in 2005 all Mustangs used this type of brake boost. I can tell you from experience that in all of the SN95 braking applications the all around best MC is one with a 1" bore and to utilize the 1993 Cobra booster as it has a Fox bolt pattern and takes very little modification to fit in our cars.

    Okay, so with all of that said I see instances where we discuss swapping to another master cylinder due to some kind of brake swap scenario and we discuss soft pedals, hard pedals, lack of brake power, air in the lines, bench bleeding the MC, etc. The one thing I personally have never thought to bring up is the booster rod adjustment. This is pretty critical being that if the gap between it and the MC piston is excessively large you will have lots of pedal travel and not much braking power and if there is no gap or tool little gap the booster rod can pre-load the piston and cause the brakes to drag.

    I have been taught how to work the math using a straight edge and a caliper (not the brake kind the measuring kind) to correctly adjust the booster push rod. 83TB and I were having this discussion and I was trying to figure out how to explain this without the hands on (that is how I learn the best) so I told him to let me research it and see if I could find it somewhere. I found it on Maximum Motorsports website on everyone of their master cylinder adapter kit installation instructions. You can go here and access them and the instructions on how to do this are in the first and second pages:

    http://www.maximummotorsports.com/Install.aspx

    And for the lazier bunch of us here it is:

    mm-mmbak2_Page_1.jpg

    mm-mmbak2_Page_2.jpg

    Hopefully this will help some folks out as I realized I did do this on my Coupe but did not do this on my Bird when I converted the brakes so I will be checking it this weekend.

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    Good points and results. I went through this on a MC swap but luckily I was still within spec.
    84 COUGAR/88HO, 1.7RRs, performer RPM,700DP, equal length shorties, stainless EXH ,T-5,Hurst pro-billet, KC clutch, 8.8/ 4.10s, line-lok, bla ,bla, bla.
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    I went ahead and printed that page off, but have not had the chance to adjust mine, but will report back as soon as I do.

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    Coolcats says the 1988 MC is 1", is that correct?

    What size would I need for TC disc rear and 60mm brakes up front... 1" or 1 1/16", etc.
    Mike

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    Soooo the 93 Cobra has 60mm fronts and TC rears and it has what size MC???

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    I want to add to this thread a tad. Using copper nickle brake line makes this remove and replace of the master much easier because of how the lines easily flex and bend.


    we also while doing my son's 88 bird went through a dozen or more trial and errors to get the booster rod in the correct spot.
    what we concluded was that with one man in the car using your hand to push the brake pedal,, and another man holding the master, as the pedel is pushed you can "feel" the booster rood bump into the master. Visa Versa the man holding the master can feel the impact as well.
    we concluded that after over a dozen attempts to get this part right that the rod needs to be damn near touching but "not".

    now we have a value and a process that gets us close.

    this does not account for the linkage slack on the pedal arm so beware of that.

    simply doing this process and thinking your right,, you will find what we found......... the "other slack" up inside the car needs brought into the adjustment as well.

    the only way we found to get this right required two people to do the "feel" method.

    if only one man,, then a work around to compensate for the pedal pivit pin slack is to shim the correct side of the pin (between the pin and the fire wall). ~this would simulate foot presure being applied to take up that slop.

    this ajustment is finite and very very meticulous... at some point you can find that even 10deg of a turn and your either wrong too tight or too loose. its a sweet spot thats hard to find.

    good thread!!

  7. #7
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    i had to look up this info in the shop manual because i didnt ever recall anyone here disussing this mystery adjustment....

    link to thread here.. and how we had to do some "inital" trial and error.

    As a note,, if your too tight,, here is the test..
    with car on level ground if you put it in gear with no brake pedal applied and the car does not roll easily forward on its own,,, your wrong.
    within three or four easy adjusments using the above method we were in the ball park. mason continued over the course of the next couple of weeks off and on doing tinny tiny tweeks to the spot he liked.


    http://www.foxtbirdcougarforums.com/...complete/page4

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