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Discussion Starter #1
*Admins, if this is not an appropriate place to put this, please move it or let me know *

Hey All,

I finally finished up my brake upgrade on my 92 Fox. Here's the current setup.

2002 13 inch dual piston PBR's upfront
1993 Cobra 11.65 inch single piston disc out back.
1993 Booster (I can't find my receipt yet)
1993/95 MC (2 port)

I finally have brakes working, though not great, I think I need to bleed them some more. But my issue is that after this last session of rebleeding everything (MC and brakes), I have a pedal that is hard has a rock about half way down. I just about have to stand with two feet to get this thing stopping good.

My guess is that my booster / MC is setup in the wrong combo. Anyone chime in here who has a similar setup?

Thanks,
 

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The hard brake pedal is probably your MC. When swapping over to 13 rotors and cobra calipers (I know you don't have) but leave the stock gt mc (in 94/95 cars) the brake peddle is harder. Swapping over to the cobra mc fixes that issue. I believe the 94/95 mc uses a 1 1/16 bore and the cobra mc uses a 15/16 bore.
 

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If you have 13" front rotors, then you must have the dual piston PBRs which are the Cobra front calipers as opposed to the GT calipers, which must use the GT 10.9" rotor.

The 93 Cobra rear brakes were 10.5" discs, not 11.65" discs. If the rear rotors are 5 lug, then you have 11.65" discs which are the 94+ Cobra rear brakes.

If your m/c is a 93/93R/95R Cobra model, then it is 1" diameter. This combination of parts should have a slightly stiff pedal. The stiff brake pedal means that you don't have any air in the system. I would try two things.

1) Make sure your brake pads are properly bedded in. Some pads will require a lot of pedal pressure until they are bedded to the rotor.

2) You may not have enough assist from your power brake booster. If your engine has reduced vacuum (nonstock cam) or your booster leaks, you won't have enough assist from it. You might need to get a M-2300k booster which has more piston area for more assist, especially if this installation is in a Fox Mustang.
 

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Discussion Starter #4
Thanks Jack for letting me know what I actually have. I bought most of this stuff off a guy and I lost the exact details of everything.

Can you clarify by what you mean with 'bedded in'?
 

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Discussion Starter #9
so an update from today. I re-bled the calipers again, and brakes are slightly better. What I do notice is , is what seems to be as not enough vacuum.

While driving, if I hit the brakes, and then go to pump the brake a second time, it feels as if the pedal hasn't come all the way up yet.

Likewise, while driving, I can't remember exactly when this happens, perhaps after a down shift, or coasting in neutral, but I go to hit the brakes, and I barely have to fight the pedal down to the point where it starts to brake. I know this one is a little vague, but I am not sure how to describe what I'm seeing. I'll take it for a spin tomorrow again.

I am using a 93 cobra booster, as I was trying to keep installation easy. I also am running a master that has the 15/16'' bore. I can't remember the application, but I remember measuring the bore size before I installed it. It is a two port unit.

The motor is stock as far as I know. I don't appear to have a vacuum leak as all is quiet in the under hood dept. The booster is hooked up properly.
 

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Charlie,

Idle the car with it stopped. Press down on the brake pedal once. Let it idle for a few more seconds. Shut the engine off. Press and release the brake pedal a couple of times. After a few pumps, the pedal should start to become harder to push as you use up all of the vacuum in the booster. If the pedal doesn't get harder, then the booster is either leaking down really fast or isn't working at all for some reason.

The booster has a check valve in the hose where the hose goes into the booster. Air should be able to flow from the booster side to the engine side, but not the other way. You can put the engine side of the valve in your mouth to test it. You should be able to suck that way. Then flip the valve around and make sure that you can't suck the other way.
 

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Discussion Starter #11
Some more info on this stuff...

When I press the pedal during normal driving, the pedal goes about 1/4 way down, then hits like I used up all the vacuum in the system. This is how it feels just about all the time.

Also to note with this setup, I have a 93 cobra master / booster. Did I botch this up and get the wrong combo? What would I need to change to get a 'normal' pedal?

Thanks again, i'll be checking for vacuum leaks soon.
 

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Discussion Starter #12
I just read a line from this site --> http://mjbobbitt.home.comcast.net/~mjbobbitt/mustang/mc.html

If you are planning on running the Cobra or Brembo brakes, then I would suggest the '93 Cobra or '94-95 Cobra 15/16" MC with the stock booster. This will give you a pedal that is not to hard.

It seems that I should have kept my stock booster and just upgraded to the 93 cobra master since I'm running PBR brakes up front with cobra's out back?
 

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I know what you are saying about what seems to be like you're running out of vacuum for the brakes to work. It feels like what mine is doing as well, and I have also related it to running out of vacuum. Not sure what to do about it just yet, I'm not so sure its that either though. I've got an 89, with the stock booster, and an Lincoln/SVO master cyl...I'm contemplating changing the booster and master to the 93-5 Cobra setup also...Its a lot of work to do only to find out that it really didn't do what you wanted it to, so I'm on the fence...
 

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Discussion Starter #14
More updates...

Bled the brakes again, figured out that I was running the rear calipers upside down (I'm dumb). So flipped the calipers, bled the brakes.

The pedal starts at the very top now. Braking is better. I still can't lock up the brakes, but I stop very reasonably.

I'll give it some more time to work in the pads and see how it goes. I still think I need more assist.
 

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More updates...

Bled the brakes again, figured out that I was running the rear calipers upside down (I'm dumb). So flipped the calipers, bled the brakes.

The pedal starts at the very top now. Braking is better. I still can't lock up the brakes, but I stop very reasonably.

I'll give it some more time to work in the pads and see how it goes. I still think I need more assist.
I don't get it.... how can you flip them upside down????

if you need help, I might be able to help you, I live in Oswego, IL.
 

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Discussion Starter #17
Okay, so I took the car out to the country roads today to real get the brake pads a work out, and good news, I can finally stop and lock the front. I think I'll ride this out and see how it goes over the next week or so.
 

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Charlie,

If you are running the 2002 Cobra calipers and a 15/16" master cylinder with the larger '93 Cobra booster you should be able to lock up that system with your toe! You have more mechanical advantage than even the street oriented '94/'95 Cobra system since they had smaller piston front calipers. My point is that something is wrong. It is most likely that your booster was damaged during installation. This is very easy to do. The snout that protrudes through the firewall is made out of plastic and it's a tight fit in the Fox cars. Any bit of extra force will crack it in a hurry. I suspect your system will perform about the same with your vacuum line to the booster disconnected. Also, if you look under the dash and peel back the rubber cover over the plastic snout you might see the crack. Additionally, with the engine running you might be able to hear a vacuum leak from the same spot under the dash. I'm betting on a cracked booster with this one.

Ron
 

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Discussion Starter #20
Some more updates.....

I haven't driven the car in a week or so...

I usually push the car out the garage, since starting it in my house scares my kids, only to find that I didn't have any brakes!

I usually give the brakes a quick tap to make sure they are working, but they have been working 'ok' so I didn't so it was a shock.

Once I started the car, I had brakes again.

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Checked the vacuum valve that goes into the booster, that is holding vacuum. I pulled it off right after turning the car off, and it released a big 'whoosh'.

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I'm not hearing any vacuum leaks under the dash, but I have pretty loud exhaust, so that may be interferring with actually knowing.

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I DID find what seems to be a 'crushed' vacuum hose. It comes from the stock upper manifold, and goes into the vacuum hose block on the left. I'm going to replace that hose and see if anything improves.
 
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