captdistraction
GrumpyRacer
Pulling from another thread. One of the things I'm struggling with on the racecar is getting the brake pedal throw just right to enable quick heel toe and allowing me to focus on braking deep into zones and smoothly transitioning into turn-in.
Right now, the current iteration of braking system of the car is:
S550 OPmustang 15" race kit with Performance Pack calipers, Girodisc 380x32mm discs, fresh G-loc R18 pads
Kohr Race booster/master setup (Which is some form of early S197/Pre 2011 booster/master)
(see the other thread for discussion of taper on pads)
Given the pedal travel is so long and a bit soft, its difficult to hit the heel-toe on the car. Last weekend I basically added 3/8" spacers to the brake pedal cover to lift it up which shaved 2/3 a second off my laptimes, but still wasn't ideal. I could have gone 5/8 even, but I'm still having issues grabbing either enough brake without grabbing enough throttle to defeat the brake, or being too far over and not being able to grab the gas (but getting an excellent grab on the brake).
The problem being that the depth needed for the first portion of braking requires non-human amounts of foot rotation to grab the gas if you position properly on brake with your foot. I'm very good at heel-toe, especially on the S550 (where I even spaced up the gas pedal).
I think ultimately I have too small a master cylinder diameter, and not sure what I can find for S197 that would fit. Research of other masters show that they all are basically the same (and the calipers were built around the fixed master size then boosters were different to get the target feel).
I'm considering seeing if the S550 performance pack master and or booster would work, as even though its a bit on/off in modulation, it is nicely sized and firm for the car. The firewall is different between cars, but the parts look very similar (ports on opposite side of master but not end of the world to replumb). Another thought is to get another early S197 master, and find a machine shop to bore it out to a new cup size and put new cups and seals in it. I like that from a fabrication perspective and making it work exactly for my needs, but that's just one more potential point of failure on a critical system on the car.
See below for other comments from my other thread.
Right now, the current iteration of braking system of the car is:
S550 OPmustang 15" race kit with Performance Pack calipers, Girodisc 380x32mm discs, fresh G-loc R18 pads
Kohr Race booster/master setup (Which is some form of early S197/Pre 2011 booster/master)
(see the other thread for discussion of taper on pads)
Given the pedal travel is so long and a bit soft, its difficult to hit the heel-toe on the car. Last weekend I basically added 3/8" spacers to the brake pedal cover to lift it up which shaved 2/3 a second off my laptimes, but still wasn't ideal. I could have gone 5/8 even, but I'm still having issues grabbing either enough brake without grabbing enough throttle to defeat the brake, or being too far over and not being able to grab the gas (but getting an excellent grab on the brake).
The problem being that the depth needed for the first portion of braking requires non-human amounts of foot rotation to grab the gas if you position properly on brake with your foot. I'm very good at heel-toe, especially on the S550 (where I even spaced up the gas pedal).
I think ultimately I have too small a master cylinder diameter, and not sure what I can find for S197 that would fit. Research of other masters show that they all are basically the same (and the calipers were built around the fixed master size then boosters were different to get the target feel).
I'm considering seeing if the S550 performance pack master and or booster would work, as even though its a bit on/off in modulation, it is nicely sized and firm for the car. The firewall is different between cars, but the parts look very similar (ports on opposite side of master but not end of the world to replumb). Another thought is to get another early S197 master, and find a machine shop to bore it out to a new cup size and put new cups and seals in it. I like that from a fabrication perspective and making it work exactly for my needs, but that's just one more potential point of failure on a critical system on the car.
See below for other comments from my other thread.
Long pedal/overboosted sounds like you have too much piston volume in your new calipers. That could also mean your brake bias has changed for the worse.
Bias aside, You either need a larger master cylinder to better match the increased volume of your calipers, or pick a caliper that has a properly sized pistons for your brake system.
Is it a new caliper? If not you may have a sticking piston. 2pc rotors help a little.
unfortunately there's no master cylinders I can change (05-09 all had the same size piston internally from my understanding). I'd love to investigate retrofitting the the proper S550 master/booster but I imagine that takes a lot of fabrication.
That said, calipers have about a year on them, they were new.
The respective brembo caliper piston specifications are:
Piston Diameters (mm)
05-14 GT: 44, 40
07-12 GT500: 44, 40
13-14 GT500: 38, 34, 30
2015 GT PP: 36, 36, 36
Piston Diameters (inches)
05-14 GT: 1.73, 1.57
07-12 GT500: 1.73, 1.57
13-14 GT500: 1.50, 1.34, 1.18
2015 GT PP: 1.34, 1.34, 1.34
Piston Area (one side of caliper)
05-14 GT: 4.30 in^2
07-12 GT500: 4.30 in^2
13-14 GT500: 4.26 in^2
2015 GT PP: 4.73 in^2
The increased piston area of an S550 caliper will result in longer pedal travel, but the system will generate more clamping force if you do not run out of pedal travel (i.e. pedal contacts floor).
But, you also changed your master cylinder. If the new master cylinder has a smaller piston than the one it replaced, this will also result in a longer pedal.
Find out what the piston size of your current master cylinder and the size of the original unit. I suspect you might have installed a smaller master cylinder while at the same time moving to a front caliper with greater piston area and volume.