91 IRS swap MC/booster combo - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 16 Old 06-06-2019, 09:22 PM Thread Starter
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91 IRS swap MC/booster combo

Hello, wanted some clarification on this topic as I am inexperienced with this level of modification.

I am in the process of IRS swapping my 91 lx and wanted to know what brake master cylinder and booster combo would work best for a mostly street driven set up?
I'm running 03/04 Cobra brakes upfront and bought a 1" 93 cobra MC. I want to know if this will work with the stock booster or if I need the 93 cobra booster for better feel. Thanks.

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post #2 of 16 Old 06-06-2019, 11:38 PM
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you want the 94/95 cobra 15/16" bore mc

and the booster

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89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #3 of 16 Old 06-07-2019, 09:57 AM
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I run the 1" 1993 Cobra MC and booster. Brakes feel really good to me.


IRS uses the same 11.65" rotors and 38mm calipers as any of the solid axle cobras and all 94-04 Cobras (and machs and Bullitt). The only difference is the 99-04 Cobra/Mach/Bullitt calipers are dual piston 40mm units and the 94-98 Cobras used the 38mm dual piston units.

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post #4 of 16 Old 06-07-2019, 11:19 AM
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HAVING the 99-04 front calipers, may allow use of the 1” bore mic to be acceptable

Forgot about the larger pistons

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #5 of 16 Old 06-07-2019, 02:15 PM Thread Starter
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Ok thanks for the replies, think I'm going to go 1" MC with stock booster and go from there. I've read 94/95 cobra boosters are the same specs as 93 just with different mounts? In another thread Jack stated MM doesn't recommend going with the 1" MC.

Sidenote, Indy, you have any insight into retaining correctly working A/C with an electric fan set up? Thanks
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post #6 of 16 Old 06-07-2019, 07:42 PM
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my 95 cobra booster, is no where near a stock booster

I have driven a car with a 1" mc, and it had no modulation compared to the 15/16"


Fan control is easy, use pressure switches

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #7 of 16 Old 06-08-2019, 03:02 AM
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All SN95 vacuum boosters have the same performance curves as the 1993 Mustang Cobra booster, but the SN95 Mustang booster has all four studs in different locations for the hole pattern in the SN95 firewall.
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Last edited by Jack Hidley; 06-12-2019 at 08:56 PM. Reason: fixed typo
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post #8 of 16 Old 06-12-2019, 01:06 AM Thread Starter
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Quote:
Originally Posted by indy2000 View Post
my 95 cobra booster, is no where near a stock booster

I have driven a car with a 1" mc, and it had no modulation compared to the 15/16"


Fan control is easy, use pressure switches
Would that run the fans when the A/C is switched on? I want them independent from each other so the car can get to operating temp.
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post #9 of 16 Old 06-12-2019, 01:18 AM Thread Starter
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Quote:
Originally Posted by Jack Hidley View Post
All SN95 vacuum boosters have the same performance curves as the 1993 Mustang Cobra booster, but the 1993 Mustang Cobra booster has all four studs in different locations for the hole pattern in the Fox firewall.
So SN95 boosters have the same bolt pattern as a regular fox body? How do you guys know all these stuff?? haha
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post #10 of 16 Old 06-12-2019, 03:16 AM
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Quote:
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So SN95 boosters have the same bolt pattern as a regular fox body? How do you guys know all these stuff?? haha
I'll be able to confirm this question when a 95 booster goes into a 79 later next week.

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post #11 of 16 Old 06-12-2019, 10:01 AM
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Quote:
Originally Posted by spencerlbutler View Post
So SN95 boosters have the same bolt pattern as a regular fox body? How do you guys know all these stuff?? haha
No they don't. The 94-95 SN95 booster is the same as the 1993 cobra booster except the stud pattern into the firewall is different. ONE stud is in a different location, and installing this booster means slotting the firewall for that stud.

Also, the threading on the studs is metric, so make sure if you install one of these you have a set of nuts that will fit the studs. The 1993 cobra booster uses the same SAE threading as the standard fox booster, so the existing nuts work

96-98 V6 boosters have a straight booster arm that connects to the pedal. You don't want this. You need the curved arm found on the 94-95 boosters. The 99-04 V6 booster may be identical to the 94-95 booster but i've never really checked out out well enough to say this with certainty.

I installed a 94-95 booster in my car. If i could go back...stick to the 1993 cobra booster.

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post #12 of 16 Old 06-12-2019, 10:08 AM
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I picked up a new booster for $12 so I figured at worst moving a bolt hole was easy

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post #13 of 16 Old 06-12-2019, 08:57 PM
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Fixed my typo above.

All four studs in an SN95 booster are in different locations than on a Fox booster.

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post #14 of 16 Old 06-13-2019, 09:51 AM
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That's interesting. I only had to slot for one stud when i did my 94-95 booster. However that was 10 years ago so perhaps i'm a bit fuzzy on that.

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post #15 of 16 Old 06-13-2019, 09:55 AM
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The holes in the Fox firewall are much larger than the 8mm studs on the SN95 vacuum booster. All the studs are in a different location between the two boosters. You may only have to slot one of the holes in the Fox firewall to get the SN95 booster to fit, but then that means that the booster is almost certainly not in the correct location.

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post #16 of 16 Old 06-13-2019, 12:41 PM
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Well fortunately that will be corrected this fall when I pull my engine and swap the booster out for a nicely painted 93 Cobra unit.

Mike
--1988 Mustang LX 5.0--
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