Brake Upgrade: Pedal Hard As A Rock - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 32 Old 09-07-2009, 08:32 PM Thread Starter
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Brake Upgrade: Pedal Hard As A Rock

*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,


Charlie R
1992 GT | AutoX / Weekend Cruiser
Killing them with 10 inches of body roll
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post #2 of 32 Old 09-07-2009, 09:02 PM
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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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post #3 of 32 Old 09-08-2009, 04:02 AM
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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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Last edited by Jack Hidley; 09-08-2009 at 11:18 PM.
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post #4 of 32 Old 09-08-2009, 08:11 AM Thread Starter
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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'?

Charlie R
1992 GT | AutoX / Weekend Cruiser
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post #5 of 32 Old 09-08-2009, 11:38 AM
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http://www.stoptech.com/tech_info/wp...formance.shtml

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post #6 of 32 Old 09-08-2009, 11:45 AM Thread Starter
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Bookmarked. Thanks for the link.

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post #7 of 32 Old 09-08-2009, 10:39 PM
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Quote:
Originally Posted by Jack Hidley View Post
If your m/c is a 93/95 Cobra model, then it is 1" diameter.
93 cobra mc has a 1'' bore, 94/95 cobra use a 15/16 bore. Note sure how much of a difference it makes but they are different.

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post #8 of 32 Old 09-08-2009, 11:19 PM
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Correct. I forgot to put the R after 95. I've edited the post to correct it.

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post #9 of 32 Old 09-09-2009, 01:11 AM Thread Starter
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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.

Charlie R
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post #10 of 32 Old 09-09-2009, 01:24 AM
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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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post #11 of 32 Old 09-12-2009, 01:14 PM Thread Starter
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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.

Charlie R
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post #12 of 32 Old 09-12-2009, 01:22 PM Thread Starter
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I just read a line from this site --> http://mjbobbitt.home.comcast.net/~m...ustang/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?

Charlie R
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post #13 of 32 Old 09-12-2009, 03:10 PM
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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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post #14 of 32 Old 09-12-2009, 05:18 PM Thread Starter
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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.

Charlie R
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post #15 of 32 Old 09-13-2009, 09:10 AM
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Quote:
Originally Posted by sprayin50 View Post
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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post #16 of 32 Old 09-13-2009, 01:38 PM Thread Starter
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By flipped I mean I had them on the wrong side - L vs R.

Charlie R
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post #17 of 32 Old 09-13-2009, 05:54 PM Thread Starter
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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.

Charlie R
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post #18 of 32 Old 09-16-2009, 04:07 PM
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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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post #19 of 32 Old 09-16-2009, 04:17 PM Thread Starter
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Thanks Ron, I'll investigate further this weekend hopefully.

Charlie R
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post #20 of 32 Old 09-27-2009, 05:55 PM Thread Starter
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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.

---

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'.

---

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

---

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.

Charlie R
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post #21 of 32 Old 09-27-2009, 09:14 PM
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keep us updated. Hopefully I learn by your mistakes!

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post #22 of 32 Old 09-29-2009, 08:16 PM
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I have the same setup pretty much.

2003 Mach 1 front brakes
Rear 11.65" SN95 brakes
SN95 booster

But i'm using a 1993 Cobra 1" MC.

My pedal feels great and I can easily modulate the pedal and lock up if i choose to. I love how it feels but i am debating swapping to a 15/16" MC just to get more of that "street car" braking feel where pedal effort is light.

Mike
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post #23 of 32 Old 01-22-2013, 11:28 AM
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Very old thread but my situation is very similar. My car is a 92 with stock front brakes and with ford motorsport rear disc setup (turbo coupe/ 93 cobra setup) I have replaced my booster, and rebuilt the master cylinder which is a 86 svo/lincoln. I have bleed the brakes several times and still cant get the brakes to lock up period. I bench bled the mc. The first time I hit the brakes the car slows but wont lock up. It is impossible to lock up the brakes!!!

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Last edited by Sk33t3r; 01-22-2013 at 12:21 PM.
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post #24 of 32 Old 01-22-2013, 11:54 AM
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Brake Upgrade: Pedal Hard As A Rock

Your master cylinder is too big, get the 1" or 7/8" and it will improve pedal feel.

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post #25 of 32 Old 01-22-2013, 12:27 PM
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Quote:
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Your master cylinder is too big, get the 1" or 7/8" and it will improve pedal feel.
Its a 1 1/8 that came on the car and im not worried about pedal feel, i just want to be able to STOP the car.

92 LX Coupe 306, TFS Street Heat Heads, VORTECH S-Trim, 18 lbs of boost.
http://www.youtube.com/watch?v=iObf3U10KkY

Last edited by Sk33t3r; 01-22-2013 at 12:58 PM.
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post #26 of 32 Old 01-22-2013, 01:38 PM
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Quote:
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Its a 1 1/8 that came on the car and im not worried about pedal feel, i just want to be able to STOP the car.
And that is directly tied into master cylinder choice.

Your current setup is a 1993 Cobra brake setup, which runs a 1" bore master cylinder.

You are currently running a 1 1/8" bore MC that ONLY works with the SVO disk brake setup (73mm fronts, 54mm rears). That's a HUGE difference.

With a larger bore MC, your pedal will be harder and it will take a TON more leg force to stop the car.

A smaller bore MC increases your mechanical advantage, making the pedal lighter and requring less leg force.

So, i'll second the recommendation to swap to a 1993 Cobra 1" MC.

Mike
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post #27 of 32 Old 01-22-2013, 09:01 PM
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Any idea what MC have a 1" or 7/8" bore with SAE threaded lines, my lines are SAE and not metric

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http://www.youtube.com/watch?v=iObf3U10KkY
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post #28 of 32 Old 01-22-2013, 09:08 PM
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Pre-1986 master cylinders are SAE threaded. There's a few different bore sizes though.

http://1985mustanggt.com/Reference/2...ng_MC_Info.pdf

Not listed is the early 7/8" bore manual Brake MC

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post #29 of 32 Old 01-22-2013, 09:16 PM
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1979-81 power and manual are both 7/8" with SAE outlets.

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post #30 of 32 Old 01-23-2013, 09:53 AM
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Sk33t3r,
like Mustang5L5 stated, you need to change your MC.

I to have the Turbo Coupe/93 Cobra Brakes with Stock 84 Booster.
The Techs over at MM suggested going with either of these MC's:

1994 Cobra: 15/16"
1993 Cobra: 1.0"
1994 GT: 1-1/16"

These will provide different pedal feel from softer to firmer.

I went with the middle ground and used the 93 Cobra with their brake line conversion kit for my 84.

You could get a MC from them "BMC-2" and use their "MMBAK-3" brake line conversion kit for your 92.

I assume you also have an adjustable PV ?

As a side note, I cannot lock my Brakes either, maybe due to the Tires I'm running, but the Car stops well and Brake feel is much better.

I'm using HawkHP Pads.

Hope this helps,
Scott

84 GT, 5.0l, 5spd, SFC'S,LCB, 5300C Springs, Koni Reds, MMCC Plates, Cobra MC, Turbo Coupe Rear Disc&North Racer Brackets, 5 Lug with Tri-Stars, Alum DS, K&N, 86-93 exhaust/Dyno-Max Cat Back & Holley Street Avenger 570....Auto-X'er
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post #31 of 32 Old 01-24-2013, 10:14 PM
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Well after some digging around I found that Cardone part number 10-1868 of a 82 ford escort has Bore Diameter: 21mm 0.826, Primary 9/16 0.5625"-18 , Secondary 7/16 0.4375"-24, the line size are identical to the svo master cylinder, and has a much smaller bore size, 21mm versus 1 1/8" which is 28.5mm, so its 7.5mm smaller. I also talked to the auto parts, they have replaced the brake booster, since I already have the master cylinder off might as well replace the booster again.

92 LX Coupe 306, TFS Street Heat Heads, VORTECH S-Trim, 18 lbs of boost.
http://www.youtube.com/watch?v=iObf3U10KkY
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post #32 of 32 Old 01-27-2013, 09:45 PM
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New brake booster installed and a 82 escort master cylinder. Pedal is a bit spongy, so later this week when I have time I will bleed the brakes.

92 LX Coupe 306, TFS Street Heat Heads, VORTECH S-Trim, 18 lbs of boost.
http://www.youtube.com/watch?v=iObf3U10KkY
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