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Discussion Starter #1
I've got a set of 6P front calipers (14" rotors) and s4 rear calipers (13" rotors) on a 92 GT with a 94-95 brake booster and a 94-95 v6 master cylinder (1-1/16" bore). My issue with this setup is that the brake pedal, while somewhat firm, very easily locks up the tires. I had the fox booster and the Baer 15/16" master and found it difficult to get the tires to even lock up at all. The car's curb weight is about 3600lbs.

Does anybody here with a similar combination have any recommendations for m/c bore size and booster?

Baer did not have any recommendations and suggested I try different setups until I found one that worked.

Thanks for any help.
 

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Wish I could help but notice this type of issue often. Braking is a system that needs to work together. You have too much brake capacity for the tires/car. What pads are you using?

FWIW: I race NASA CMC and used the factory Cobra "PBR" calipers for years on a 96 SN95. I had to use a very aggressive pad to get the car to stop as quickly as needed. Last year I went to 4 piston Stoptech ST40's. The caliper was so much better I dropped several levels of pad aggressiveness to help managed wheel lock-up.....the other advantage is rotor life is much better now too. I can still lock up the wheels if I want but it doesn't happen unless I'm hard on the pedal.
 

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Discussion Starter #3
Wish I could help but notice this type of issue often. Braking is a system that needs to work together. You have too much brake capacity for the tires/car. What pads are you using?

FWIW: I race NASA CMC and used the factory Cobra "PBR" calipers for years on a 96 SN95. I had to use a very aggressive pad to get the car to stop as quickly as needed. Last year I went to 4 piston Stoptech ST40's. The caliper was so much better I dropped several levels of pad aggressiveness to help managed wheel lock-up.....the other advantage is rotor life is much better now too. I can still lock up the wheels if I want but it doesn't happen unless I'm hard on the pedal.
Thanks for your response, it is extremely helpful.

I never really considered that the braking hardware is in excess of the car itself. I simply presumed that Baer took this into account when they built the system. Clearly, I have a lot left to learn.

You bring up a great point about the pads. I never stopped to consider that the pads might simply be way too aggressive for what I'm doing with the car. If I remember correctly, Baer supplies Hawk HPS pads with their hardware. Do you think that pad is a bit too aggressive given the application? If so, what would you recommend?

Again, thanks for your reply!
 

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Discussion Starter #5
Approximately 6 months. I put a 94/95 booster in it first and I was able to lock the brakes up with minimal pedal pressure. After that I installed the larger bore master.
 

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Thanks for your response, it is extremely helpful.

I never really considered that the braking hardware is in excess of the car itself. I simply presumed that Baer took this into account when they built the system. Clearly, I have a lot left to learn.

You bring up a great point about the pads. I never stopped to consider that the pads might simply be way too aggressive for what I'm doing with the car. If I remember correctly, Baer supplies Hawk HPS pads with their hardware. Do you think that pad is a bit too aggressive given the application? If so, what would you recommend?

Again, thanks for your reply!
I'm not familiar with Baer or Hawk products and not qualified to answer your question........just pointing out what I do know and you obviously have too much brake. Whether you reduce braking capacity at the wheel or further upstream is up to you. IMO, you're wasting money on calipers that are way overkill for the application. However, they do provide "bling" if that's what you're looking for. :wink2:
 

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This is another case of the SN95 brake booster providing too much assist and making the brakes overly sensitive. The SN95 booster has about 25% more assist than the Fox dual diaphragm booster. When used with any brake rotors over 11" in a Fox Mustang, it results in too much brake sensitivity.

I asked how long the car had the original booster in it with the Hawk pads because I wanted to make sure that the pads were completely bedded into the rotors. Without this being done, the pedal effort will be higher.

I strongly suspect that the original vacuum booster was defective in some way. Possibly it was leaking or had a bad check valve.

Hawk HPS pads work very well on a street car. From your description, these are not HPS pads and/or something was wrong with the original booster. Step one is to find out from Baer what pads they are. That can make a huge difference.

With your setup I would normally recommend HPS pads, stock Fox booster and a 1" m/c. Since you found the pedal effort to be too high with one size smaller m/c either the booster wasn't working properly or the pads had much lower friction than HPS do. My guess would be that they are ceramic, which almost universally suck for performance use.
 

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Discussion Starter #8
This is another case of the SN95 brake booster providing too much assist and making the brakes overly sensitive. The SN95 booster has about 25% more assist than the Fox dual diaphragm booster. When used with any brake rotors over 11" in a Fox Mustang, it results in too much brake sensitivity.

I asked how long the car had the original booster in it with the Hawk pads because I wanted to make sure that the pads were completely bedded into the rotors. Without this being done, the pedal effort will be higher.

I strongly suspect that the original vacuum booster was defective in some way. Possibly it was leaking or had a bad check valve.

Hawk HPS pads work very well on a street car. From your description, these are not HPS pads and/or something was wrong with the original booster. Step one is to find out from Baer what pads they are. That can make a huge difference.

With your setup I would normally recommend HPS pads, stock Fox booster and a 1" m/c. Since you found the pedal effort to be too high with one size smaller m/c either the booster wasn't working properly or the pads had much lower friction than HPS do. My guess would be that they are ceramic, which almost universally suck for performance use.
Thanks for the very detailed and informative response.

Regarding the pads they are marked Hawk HPS in white letters on the back of the pad. Since you feel that the pads are a good street pad I will turn my attention to the booster. The booster that was removed to be replaced by the 94/95 booster was the original booster from 1992 so it is entirely possible something was faulty with it. I will look for a replacement fox booster and 1" bore master cylinder to remedy the overly sensitive brakes.
 

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What tires are you running? Everyone forgets to consider the issue with tires. With the setup you have I would run nothing more than 200 tread wear and nothing narrower than 245s. All season crappy tires are going to lock up easy with all that breaking power.
 

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This is another case of the SN95 brake booster providing too much assist and making the brakes overly sensitive. The SN95 booster has about 25% more assist than the Fox dual diaphragm booster. When used with any brake rotors over 11" in a Fox Mustang, it results in too much brake sensitivity.
I'm surprised you would say that, Jack, as there are plenty of happy M-2300-K users out there with 13" PBRs and the SN95 booster. I originally ran my Baer brakes (essentially a copy of the M-2300-K setup) with the Fox booster and it was terrible. I then swapped to an SN95 booster and ran the Baer/PBR setup up front for years with no issues, and now have a 13" ST40 setup up front with the SN95 booster.

i have the same brake set up as you in my 1995 gt with a 1993 cobra m/c works great.
That can't possibly be true, as t500hps has already stated that this setup is "obviously too much brake". Both you and Harry just need to throw the kits away.
 

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Pat,

I strongly suspect that the vast majority of people out there with M-2300-k installs and Fox boosters, have old boosters with one of the diaphragms torn (1/2 assist). The other major problem is that people use brake pads with very low cf. The SN95 booster is used as a crutch to get the overall sensitivity into a reasonable range. But this doesn't solve the problem of the SN95 booster having too much crack sensitivity. This makes it very difficult to modulate the brakes. Once the correct pads are installed, the Fox booster works great.

Brake systems are actually one of the easiest things to analyze in the car, but you must have every piece of information about them, and you must know that all the parts are working correctly. Every time I help a customer with a brake system that has unacceptable travel and/or effort, I'm able to fix it using fairly simple calculations partly based on known good combinations. In years of doing this, not one person prefers the SN95 booster with the M-2300-k kit, when all the parts in the system are working correctly.

My car currently has an SN95 booster (from previous owner) with a Stoptech 13" kit and a Baer 12" rear kit. Overall this base brake system has about the same sensitivity as an M-2300-k kit. The brakes suck. They are far too sensitive. When I go from the WRX to the Mustang, I lock the tires several times in the first 5 minutes of driving trying to adjust.

Earlier this year we built a Fox Mustang for Matt Farrah (Smoking Tire). The car had an SN95 booster in it when he bought it. He wanted to leave it there to save some money. We installed an M-2300-k kit that he supplied. He loves everything about the car except the overly sensitive brakes. He drives a lot of performance cars every week.

In this particular case, the posters brake system has 33.5% more front caliper area than an M-2300-k system and 8% more brake torque from the different front rotor diameter alone. Combined this gives the brakes 44% more brake pedal sensitivity than an M-2300-k system. It probably only takes 40lbs of pedal force to lock all four tires with an M-2300-k booster on this car. Not even a Cadillac owner is going to like that level of assist;)
 

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Well, I guess I have to chalk it up to different strokes for different folks. I've never felt the need to change my driving/braking style when shifting from my Subaru or CTS-V to the Mustang. Perhaps I just naturally/subconsciously adjust based on the fact the Mustang doesn't have ABS and the other two do? I dunno. FWIW, I'm 180deg opposite when it comes to the HPS pads, too - I think they're over-priced garbage. The fact that Harry's having problems locking them up too easily definitely indicates something ain't right.

Your experience (with many more cars) does make me wonder if my Fox booster was dead when I did the Baer install years and years ago. I had basically the exact opposite experience as Harry - I couldn't lock up the brakes regardless of how hard I tried. Shifting to the SN95 booster fixed that nicely. Part of me wonders what my car would be like with a Fox booster, but a much larger part of me has no desire to ever swap boosters again! :p
 

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Pat,

If your Mustang had low engine vacuum when you did the brake swap, that would also make the brake effort too high with the Fox booster. I know that the car has heads and a blower, but I don't know what the cam is.
 

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Discussion Starter #15
What tires are you running? Everyone forgets to consider the issue with tires. With the setup you have I would run nothing more than 200 tread wear and nothing narrower than 245s. All season crappy tires are going to lock up easy with all that breaking power.
I am running NT05s 285/35/18 rear and 255/35/18 in front.
 

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Discussion Starter #16
This was an interesting discussion to read, thanks for all the input. It's quite possible that the fox booster had failed over the years. It was hard to believe that I could not lock the tires even that much rotor and caliper so I went to the SN booster thinking it was a problem with the the fox booster.

Of the other cars I own, the one that is closest in terms of braking power is my 911TT. The brakes on that thing are massive and the pedal isn't overly sensitive. There is quite a lot of distance the pedal can travel before the brakes feel like they are going to start locking. In the Mustang it is quite the opposite, the brakes want to lock up with moderate pedal pressure and the area in which to modulate the brakes is very narrow.

I am running an FMS F cam so I have less vacuum assist than a stock cam.

I have been through the car many times and everything is pretty new in the braking system so I would be surprised if I had a mechanical problem.
 

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I work really close with them on a lot of builds. I'm running a 4 piston Baer setup on my car with a 93 Cobra booster paired with their Remaster. When we did my car, they recommended a 1" bore. I can't say that I'd change it at all.
 
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