MC/Cobra brakes problem

green94droptop · Oct 13, 2006

Hey guys. Ever since I changed out the stock GT brakes to Cobra Brakes (couple years ago), I have some problems with stoping the car. Basically, I've never been able to engage the ABS on the car. If I slam the pedal, the car WILL stop, eventually. The pedal doesn't quiet travel to the floor, but it comes pretty close if I slam it.

Here's what I've done in the last year to try to fix the problem:

new 2 piston Cobra PBR calipers, SS lines, 99+ 13" Brembo rotors, stock Cobra pads and new rear rotors/pads. I made sure I bled the brakes properly (farthest away from the MC) the last time I did it, using a buddy.

Everything has been replace except for the 130,000 mile old master cylinder. My question to YOU is could the MC be the culprit? Could the seals be bad inside the MC? Should I buy the Autozone Special or a Ford new one?

This whole brake thing has been annoying me over the last year or so because I can't get the car to stop like I want it.

Any advice guys?

Thanks.

94-302-vert · Oct 13, 2006

are you 1000% sure you bled the brakes entirely?

I went through almost 3 quarts of fluid bleeding mine and we went around the car like 4 times.

The other thing to check is to disconnect an ABS sensor to disable the system and see if you can lock them up. Mine easily locked up all 4...

green94droptop · Oct 13, 2006

I should have mentioned that. Yes I went through the about 2 bottles of the last time I did it. I saw new, clear fluid through all the calipers. In addition, I did disconnect the ABS system and could not lock up the wheels. Still seemed like I was trying to stop a train.

green94droptop · Oct 13, 2006

Also forgot the mentioned that I hear a very noticable hissing (sounds like an air leak) noise as I apply the brake pedal to the floor. Could this mean anything?

1TallMF · Oct 13, 2006

Perhaps the diaphragm in your brake booster is leaking?

green94droptop · Oct 13, 2006

Oh I don't want to hear that.

Chythar · Oct 13, 2006

green94droptop said:
Also forgot the mentioned that I hear a very noticable hissing (sounds like an air leak) noise as I apply the brake pedal to the floor. Could this mean anything?

I can hear that hiss when I apply my brakes. But not while I'm driving, and definitely not with the radio on, so it's not too loud. My brake pedal is close to the floor when I push it hard, but I can still slip my foot between the pedal and the floor. I still have good stopping power with the stock calipers and slotted/dimpled rotors, so something is definitely wrong with your brake system.

The description of your issue sounds to me like air in the system. When you were bleeding your brakes, did you ever let the MC empty of fluid? If so, you might have some air in the MC still. If I remember right, you can't just bleed the MC in the car - you have to take it out and "bench bleed" it. Not sure of that process offhand, maybe someone else can let us in on the secret.

94-302-vert · Oct 13, 2006

I had a heck of a time getting all of the air out of my front brakes... that is why we kept bleeding long after the fluid was clear...

green94droptop · Oct 13, 2006

Chythar said:
I can hear that hiss when I apply my brakes. But not while I'm driving, and definitely not with the radio on, so it's not too loud. My brake pedal is close to the floor when I push it hard, but I can still slip my foot between the pedal and the floor. I still have good stopping power with the stock calipers and slotted/dimpled rotors, so something is definitely wrong with your brake system.

The description of your issue sounds to me like air in the system. When you were bleeding your brakes, did you ever let the MC empty of fluid? If so, you might have some air in the MC still. If I remember right, you can't just bleed the MC in the car - you have to take it out and "bench bleed" it. Not sure of that process offhand, maybe someone else can let us in on the secret.

Ok, I like this answer better. I beleive my situation is similar to yours. I only hear the hissing sound at idle, never when I'm driving; hopefully it's not the booster. However, I could have let the MC run dry at one time. Being that I have ABS, I've heard that you have to take it to Ford to get the ABS system purged? Is this true?

JJ95GTID · Oct 13, 2006

If I am not mistaking I thought the Cobra brake upgrade for 94-95 Mustang GTs came with a new MC. FRPP part# M-2300-Q shows that it does. Maybe this is your problem

Chythar · Oct 13, 2006

JJ95GTID said:
If I am not mistaking I thought the Cobra brake upgrade for 94-95 Mustang GTs came with a new MC. FRPP part# M-2300-Q shows that it does. Maybe this is your problem

The Cobra MC preserves the brake pedal feel that you have with the stock GT brakes - sorts soft. You can use the GT/V6 MC with the Cobra brakes, but the pedal will be harder. This basically means it takes less effort to apply the brakes; the pedal is more sensitive. Several guys here use the stock MC with Cobra brakes and have no problems.

Chythar · Oct 13, 2006

green94droptop said:
Ok, I like this answer better. I beleive my situation is similar to yours. I only hear the hissing sound at idle, never when I'm driving; hopefully it's not the booster. However, I could have let the MC run dry at one time. Being that I have ABS, I've heard that you have to take it to Ford to get the ABS system purged? Is this true?

Also, if the booster was leaking your pedal would sink to the floor and you'd slowly lose brake power. Air in the lines makes the pedal feel "spongey" or "springy". I honestly don't know about purging the ABS system, but this URL seems to know what it's talking about:

http://www.veryuseful.com/mustang/tech/brakes/bleeding.html

green94droptop · Oct 13, 2006

Chythar said:
Also, if the booster was leaking your pedal would sink to the floor and you'd slowly lose brake power. Air in the lines makes the pedal feel "spongey" or "springy". I honestly don't know about purging the ABS system, but this URL seems to know what it's talking about:

http://www.veryuseful.com/mustang/tech/brakes/bleeding.html

Thanks for the link. DO MC's go bad after time? Tomorrow, I think I'm going to take off the MC and do a bench bleed, then bleed the whole system, thoroughly.

Chythar · Oct 13, 2006

green94droptop said:
Thanks for the link. DO MC's go bad after time? Tomorrow, I think I'm going to take off the MC and do a bench bleed, then bleed the whole system, thoroughly.

They have rubber seals inside, so yes. Though I couldn't tell you how long it takes for them to go bad. Though I hear remanufactured MC's tend to go bad much sooner than new ones.

Car Nut · Oct 13, 2006

I've got the Cobra brake kits front and rear with the stock MC and all is good. Over 155,000 miles on the stock MC too and no problems at all.

Pedal feel is firmer and actually perfect I think.

No problems whatsoever, so you definitely got something going on. Might be worth taking to a reputable shop/dealer and get it checked out.

You do not want your brakes failing on you at all. I'd get it checked out.

Car Nut · Oct 13, 2006

Yeah, when it comes to brakes, definitely get new parts and not remanufactured ones.

green94droptop · Oct 13, 2006

Thanks for your help guys. Tomorrow, I'm going to Pep Boys and ordering a new Genuine Ford part. Should be installed by next weekend.

green94droptop · Oct 15, 2006

Well, the brand new MC took care of my problems. My car stops like it should now. It's actualy pretty scary how well it stops.

Next project is to take care of the rest of the front end. New 03 Cobra CA's, Bilsteins all around, new MM C/C plates. Hopefully the car will be much more fun to drive now.

Thanks for your help guys!

MC/Cobra brakes problem

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