5 lug swap into 92 Fox

Discussion in 'Fox 5.0 Mustang Tech' started by clintjackson, Jun 7, 2011.

  1. After months of research and coming across a 98 Cobra, taking 3 weekends to complete the swap I am totally satisfied except for one thing. My brake pedal takes a lot, and I mean a LOT of pressure to get the car to stop. I followed all advice and instructions to the letter including replacing the MC and booster from a 95 V6. I gutted the proportioning valve as per the instructions, added the manual valve in the rear line connection near the pass firewall, and the brakes are bled to perfection. Rotors have been turned, new pads, calipers, steel braid lines, ect ect. What can I do to make the brakes feel like they are more power assisted instead of manual? Any advice would be greatly appreciated.
  2. Booster is shot perhaps?

    95 V6 MC has a 1-1/16" bore = 572mm bore area
    98 Cobra twin pistion 38mm Calipers = 38^2 *.785 = 1134mm per piston x 4 = 4536mm
    98 Rear 38mm Calipers = 1134 x 2 calipers = 2268mm

    Add the two and you get 6804mm total piston area divide the MC's bore = 11.9:1 ratio, which is on the hard side according to the site.

    If your booster is fine, you'll need to go to a smaller bore MC, 15/16" 93 Cobra will be slightly softer than the 1" 94+ Cobra.
  3. Thanks for the info and advice. Just a point of curousity, what is the bore size of the 92 stock mc? I will look for the 93 Cobra unit after I check the booster.
  4. For some reason the engineers used a metric bore 21mm IIRC on the 84?-93 V8 MCs. Keep in mind our cars having drum rears the bore size comparison is quite different when calculating using a similar bore size on 4-wheel disc.

    I bought a Raybestos MC390125, think it was only $70 couple years ago.
  5. Thanks so much for the info.

  6. That master cylinder is much too big for the 98 cobra brakes. It's a 1 1/16" bore.

    You need a 94-95 cobra master cylinder, which is a 15/16" bore. 1998 conra brakes are identical to 94-95 conra brakes...so that's the setup you want to mimic. The booster can stay....same part.

    You also need the appropriate 3-2 conversion to use this MC. May I ask how you did the conversion so I can recommend appropriate parts to use the 94-95 cobra mc?

    An easier swap than the 94/95 cobra master cylinder is the 1" bore 1993 cobra mc. It would be a direct swap for the 95 v6 mc in there now. No additional fittings needed. This was the mc ford originally intended for the 94 cobra, but ot was determined to be a tad too firm for a street car and was changed to the 15/16" bore.

    Those are your only options really. Thats the correct mc to caliper ratio. If you need more clarification, read the sticky I started at top of page. About 3-4 posts in, I explain the differences in master cylinder bore sizes and choosing the correct mc based on calipers.
  7. The car is covered now. Shaving the trunk lid of all emblems and lock. I mounted the "T" fitting off the rear port of the modified pro valve, one fitting to the pass front and the other to the back with a manual sbbc proportionvalve mounted in line near the pass side hood hinge. I have this set at three full turns out from full increase. If I find the 94/95 booster I installed turns out to be faulty, can I use the stock one?
  8. Let me double check the 3-2 conversion tomorrow. Want to make sure I'm correct in what I say.
  9. Listen to Mike about the MC bore, I mixed my response up. The 93 Cobra (which I am using) has 1" bore. and will give a slightly harder pedal than the 94/95 Cobra. My apologies...
  10. Yes you can, but the pedal will still be hard as it is a smaller unit than the 93 Cobra & 94-95 V6/GT/Cobra. Check for vacuum leaks, that can also affect the booster negatively.
  11. No. The stock fox booster has less assist.

    Assuming your current booster worked, if you put the fox booster in, the pedal would be even harder.

    WIth, the 1998 Cobra front and rear brakes, you need the 94/95 Cobra Master Cylinder, and the larger 205mm booster found in 94-95 Mustangs and the 1993 Cobra.

    For a 3-2 kit to work with that, this is the major one


    However, you may need to replumb your entire Prop valve setup to run this. The Cobra MC has the fitting sizes reversed to prevent accidental assembly line mixups with the GT/V6 MC you have installed now.

    An EASIER MC swap would be the 1993 Cobra MC, but you should change your front calipers out to the 99-04 Cobra calipers that feature 40.5mm piston bores. The 1998 Cobra features 38mm pistons
  12. I thank both of you for all the advice and opinions. its great to have such a good resource. Maybe I tried to absorb way too much info once I decided to take the plunge. Since I now have more money into this suspension/brake swap than I paid for the car I need to utilize most of what I have. In a nutshell, I'll buy a 95 gt mc and the 3-2 adapter and use the larger booster. Hopefully this will give me a pedal that feels more like it used to. As long as it stops better! That was the main objective anyway. I appreciate your time and expertise. Unless you can think of something else major, I'll post next week with an update.
  13. You mean 94-95 Cobra MC?
  14. Yes, that's what I meant.
  15. Going back up to the 3-2 adapter, is the one listed still the one to get with the cobra mc?

  16. I'm sorry. I listed the wrong one. :( I feel badly if you didn't ask and had bought the incorrect one based on my post

    It's this one

    Master Cylinder adapter Kit, 94-95 SVT master cylinder, 87-93 Mustang, stock lines [MMBAK-8] : Maximum Motorsports, the Latemodel Mustang Performance Suspension Leader!

    94/95 SVT MC with 87-93 stock lines. You will have to adapter to whatever you did for your conversion though. Assuming you can go back to stock, you can use this kit.

    Sorry bout that

    Just to confirm, you are sure these are 1998 cobra front brakes??? Not 99-04 at all?
  17. Confirming they are 98 Cobra. Thanks.
  18. In that case, that is in fact the MC to use
  19. I'd like to say 'last question' but it wasn't clear if I needed to have the stock proportioning valve back together as it was or if the gutted version could be used with adapter #mmbak-8.
  20. Gutted version is fine.

    I just wasn't sure if you had cut/flared the lines to something far from stock