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  1. #1

    Default 94-98 GT/V6 Front Calipers With Rear Drums. What Master Cylinder Do I Use?

    Hi gang, first post here.

    I have a 1986 convertible I did the SN95 front conversion on using the 1994-98 GT/V6 single 66MM calipers and am running my stock rear drums that have been freshly rebuilt. I did this conversion just so I could run the 18" wheels my son and I picked out. After completing the conversion I noticed the stock master cylinder is wet underneath and looks like it may be leaking from the rear seal. The pedal has too much travel at the moment and I am not sure if it is the leaky MC or the fact that the front calipers are larger or both. Since I will be replacing the MC do I replace it with the stock 86 MC or upgrade it to a different one? I have read through many many threads and cannot find my answer. The closet this I could find was a similar situation where Jim Hidley suggested running a 1994-95 Cobra MC with a 15/16" bore and gut the factory proportioning valve and install an adjustable. I also read some good information from Trey @wraithracing but still am not certain which way to go. I will be placing an order with Maximum Motorsports but not positive what to order yet. Any help would be greatly appreciated.

    John
    Last edited by johnnyhorsepower; 03-24-2022 at 07:58 AM.

  2. #2
    Moderator wraithracing's Avatar
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    Personally I would stay with the OEM M/C to start with. Completely bleed the system and see how everything works and feels. All the SN95 M/C's will require either adapter brake lines or cutting and reflaring due to metric fittings. They are all also designed for rear disc which you don't have. Most likely the stock M/C will do just fine even with the slightly larger front calipers. If the brake pedal still feels mushy or soft, then you might need to go from the stock 22mm to an SVO style 1". There is a direct swap 1" M/C that I believe is off an earlier Ford model, but I would have to do some searching to verify what model. Good Luck!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  3. #3

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    Quote Originally Posted by wraithracing View Post
    Personally I would stay with the OEM M/C to start with. Completely bleed the system and see how everything works and feels. All the SN95 M/C's will require either adapter brake lines or cutting and reflaring due to metric fittings. They are all also designed for rear disc which you don't have. Most likely the stock M/C will do just fine even with the slightly larger front calipers. If the brake pedal still feels mushy or soft, then you might need to go from the stock 22mm to an SVO style 1". There is a direct swap 1" M/C that I believe is off an earlier Ford model, but I would have to do some searching to verify what model. Good Luck!
    I agree. Stay with the stocker for time being. The SVO 1-1/8" will be too much, but the 1" may fit the bill. I've used it on a couple cars that I wanted to keep the original style MC on.

    The application is a 1980 Lincoln Mk VI. 1" bore. There may be an adapter fitting needed on the primary port, but it's not a huge deal.
    83 TC "Clone"
    85 Marquis LTS
    86 LTD Wagon

  4. #4
    Moderator wraithracing's Avatar
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    Quote Originally Posted by Chuck W View Post
    I agree. Stay with the stocker for time being. The SVO 1-1/8" will be too much, but the 1" may fit the bill. I've used it on a couple cars that I wanted to keep the original style MC on.

    The application is a 1980 Lincoln Mk VI. 1" bore. There may be an adapter fitting needed on the primary port, but it's not a huge deal.
    That is the one I couldn't rememeber. I also meant to say Stock not SVO style 1".
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  5. #5

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    Thanks for the replies guys! At the moment the pedal has too much travel but like I said I have discovered the original MC appears to be leaking from the rear seal so without replacing it first with another oem I will never know if the 21 MM MC will work for me. I understand moving to a larger bore MC will reduce this. So the 1980 Lincoln Mk VI MC with a 1" bore would be the way to go because it is designed to work with rear drums or because it is easier to plumb in? Both the 1994-95 Cobra MC with 15/16" bore and the 93 cobra MC with the 1" bore have adapter lines offered by Maximum Motorsports to simplify the installation so I would not be opposed to that. I just did not know if it would not work as well as the 1980 Lincoln MC because they were designed to work with rear disc? Also, if replacing the front calipers with 13" 99-04 Cobra dual piston calipers with smaller surface area and keeping the oem style MC would be better I would not be opposed to doing that either. Sorry for all the questions I just want to get this as good as it can be without converting to rear discs if possible.

    John
    Last edited by johnnyhorsepower; 03-24-2022 at 11:37 PM.

  6. #6
    FEP Super Member
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    Since you are doing so much hodge-podge trickery with your set-up: Go with the 1" bore master, gut the factory proportioning valve and install an adjustable valve in the rear brake lines. The larger bore will give you the fluid VOLUME while the adjustable valve will allow rear bias dial-in. Or quit dingling around and go rear disc and use the TurboCoupe factory proportioning valve with the 15/16" master........
    " If you're not living life on the edge, that means you're taking up too much room."
    1979 Mustang Indy Pace 2.3T/4spd (sold on 1/10/16)
    1983 GLX vert 3.8/auto (triple black, sold on 10/8/13)
    1984 (early) Turbo GT (parts SLOWLY coming together)
    1985 Coupe 4.6L DOHC/IRS swapped (sold 9/10/17)
    1986 GT TTop 5spd (sold as of 10/8/13)
    1988 Thunderbird TurboCoupe (Cobra IRS/Brakes/big turbo project)

  7. #7

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    The Mk VI 1" MC is inexpensive (Like under $40 on RA)and will work fine for what you're doing. That, plus the adapter, will be all you need. (I think it's a 7/16 INF fitting on your current MC and a 1/2" INF on the Mk VI one) It might give a slightly more firm pedal.

    The Mk VI was disc/drum with larger bores on each.

    I've used this MC on cars with the 99-04 twin piston calipers, which have about the same total bore diameter as the single piston ones from the earlier SN-95's. As well as a couple other set-ups.

    I wouldn't worry about messing with the prop block until you have a chance to drive the car. I didn't mess with it, as the car stopped fine under hard braking.

    On the '80 XR-7 I had with the bastard brake set-up (C4 Vette 12" in the front and SVO/Lincoln in the rear) I also used this one, but I did do the conversion to an adjustable prop valve, but did use the 1"-bore Mk VI MC.
    83 TC "Clone"
    85 Marquis LTS
    86 LTD Wagon

  8. #8
    Moderator wraithracing's Avatar
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    As Chuck W mentioned plumbing in the 80 Mark VI M/C should be the easiest and probably not have to mess with the Proportioning valve (MAYBE).

    You can install the 94/95 Cobra M/C and use the MM brake line kit, but you will need to gut the stock prop valve and install an adjustable. So overall cost is increased as well as additional labor to make it all work. Since you need a new M/C its a bit more of a wash and ultimately dependent upon your budget and desires. Good Luck!
    Last edited by wraithracing; 03-25-2022 at 01:53 PM.
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  9. #9

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    Quote Originally Posted by wraithracing View Post
    the 80 Mark VII M/C
    Mark VI, not Mk VII (Typo, I'm sure)
    83 TC "Clone"
    85 Marquis LTS
    86 LTD Wagon

  10. #10
    Moderator wraithracing's Avatar
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    Mark VI, Mark VII, Mark VIII they're all the same right!
    My fat fingers at work again!
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
    1969 Mach 1
    1979 Pace Car now 5.0/5 speed
    1982 GT Stalled RestoModification
    1984 SVO Still Waiting Restoration
    1986 GT Under going Wide Body Conversion Currently

    Current Capris:
    1981 Capri Roller
    1981 Capri Black Magic Roller Basket Case
    1982 Capri RS 5.0/4spd T-top Full Restoration Stalled in TX
    1984 Capri RS T-top Roller
    1983-84 Gloy Racing Trans Am/IMSA Body Parts

  11. #11

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    I picked up an oem master cylinder today to replace the leaky one and plan on installing it this weekend to see how it responds. If it is sufficient I will roll with this one and if it leaves much to be desired I’ll make a decision on what my next move is base on everyone’s feedback.

    Thank you for all your input !!
    John

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