Cobra Brake Swap Issues

So your situation has gotten me thinking, Cobra brakes are not known for strength. I know GMAN picked those calipers up as remans from the parts house...guys have been know to turn in Cobra calipers as cores that have been spread from heat/extreme use. With reman quality control being what it is I wouldn't be surprised if this was the cause of your issues. When you put a lot of pressure to them the stressed caliper bridge is flexing instead of applying pressure to the rotor.

-Alan
 
lobird91 said:
So your situation has gotten me thinking, Cobra brakes are not known for strength. I know GMAN picked those calipers up as remans from the parts house...guys have been know to turn in Cobra calipers as cores that have been spread from heat/extreme use. With reman quality control being what it is I wouldn't be surprised if this was the cause of your issues. When you put a lot of pressure to them the stressed caliper bridge is flexing instead of applying pressure to the rotor.

-Alan
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I would agree with you on this, however, the issue existed before he swapped to the Cobra brakes, leading me to believe it's not the calipers.

Front calipers, soft lines, rotors, and pads have been replaced. Rear lines, rotors, and pads have not been touched since I bought it.

Master cylinder and booster have been replaced.

So rear soft lines, proportioning valve, vacuum leak, or air in the lines. That seems to be what it's narrowed down to.
 
You never mentioned how the pedal felt. If the pedal is not firm about an inch down you probably have air in the lines. The problem is the length the air bubble would have to travel just to the abs pump is impossibly. You bleed the wheel but there is not enough fluid travel to get the air bubble to clear the abs pump. Sure it gets moved but by the time you try the second bleeding process it has already moved up the line. No matter how many times you try and get rid of the air bubble it just kinda stuck between the master cylinder and the abs pump. Let the car sit a few hours or over night. Bleed the master cylinder. It took me about 3 cans of brake fluid, several sessions of bleeding all the wheels and hours of frustration.

As far as the Cobra calipers, I have open tracked my cobra since the first weekend i bought it. I have found that the calipers don't spread they just don't have enough clamping force when pushed really hard. Going from 120mph down to 30mph they were fine but 122mph down to 30mph they just couldn't clamp down on the brakes pads hard enough. I have gotten them so hot they smoked before, forgot to turn on my brake fans.
 
racebronco2 said:
You never mentioned how the pedal felt. If the pedal is not firm about an inch down you probably have air in the lines. The problem is the length the air bubble would have to travel just to the abs pump is impossibly. You bleed the wheel but there is not enough fluid travel to get the air bubble to clear the abs pump. Sure it gets moved but by the time you try the second bleeding process it has already moved up the line. No matter how many times you try and get rid of the air bubble it just kinda stuck between the master cylinder and the abs pump. Let the car sit a few hours or over night. Bleed the master cylinder. It took me about 3 cans of brake fluid, several sessions of bleeding all the wheels and hours of frustration.

As far as the Cobra calipers, I have open tracked my cobra since the first weekend i bought it. I have found that the calipers don't spread they just don't have enough clamping force when pushed really hard. Going from 120mph down to 30mph they were fine but 122mph down to 30mph they just couldn't clamp down on the brakes pads hard enough. I have gotten them so hot they smoked before, forgot to turn on my brake fans.
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Pedal feels pretty firm and doesn't seem like I can depress it all the way.

How do I bleed the master cylinder?

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chris2523 said:
stiff pedal means no vacuum brake assist.

do you have a stiff pedal?
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Replied over on LOD as well, but I did the test driller mentioned. The pedal goes soft once the car starts, but it seems awfully firm when driving and you nail the brakes. Seems somewhat less firm if you ease into them, but still more firm than any other car I've ever driven, to include those without power brakes.
 
I wonder if the rubber o-ring between the master cylinder and booster was installed...
 
Dan I was wondering that myself or if it is installed, is it in correctly. There have been threads about it being twisted and creating a vac leak and braking problems. Would be something to check carefully.
 
DieselDan said:
I wonder if the rubber o-ring between the master cylinder and booster was installed...
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It's really hit or miss. Sometimes the pedal is normal but terrible braking and other times it's stiff with terrible braking. I want to get it figured out so I can drive the car without worry.

LSC HUNTER said:
Dan I was wondering that myself or if it is installed, is it in correctly. There have been threads about it being twisted and creating a vac leak and braking problems. Would be something to check carefully.
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I'm not sure I'm mechanically inclined enough to do this. I can do a lot of things but braking systems scare me.
 
If it's intermittent as suggested, I would also suspect the vacuum leak issue at the booster/master cylinder assembly.
 
driller said:
If it's intermittent as suggested, I would also suspect the vacuum leak issue at the booster/master cylinder assembly.
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I don't think it's the hose itself. Can I buy the check valve separate? It's the gray 90 piece, right?
 
The check valve is available but the topic at hand is the o-ring seal between the master cylinder and the brake booster.
 
You know, it was unbolted the other day and I don't recall even seeing one there.

There shouldn't be any issues with me removing the two bolts from the master cylinder to the booster, right? If not, I'll crack that open and see if the o-ring is there. Something tells me there isn't.

I'll check tonight after work.
 
Thank you to mad1stgen yesterday for fixing me up with the o-ring between the master cylinder and the brake booster.

I finally have brakes! Now for some better pads with a better heat range.
 
lobird91 said:
Awesome, glad you got it worked out.
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Martin and J were the guys that figured it out. Apparently it's a common issue when the booster or master gets replaced.

LSC HUNTER said:
Bingo!!

Sometimes the smaleest of things can cause hair loss!!!
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I'm just glad it's finally fixed. I can actually drive it now.

dnsherrill said:
Wagner Thermo-Quiet?
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Probably StopTech Street Performance. I like to autocross and I want to take the Mark out.

DieselDan said:
Woo-hoo! I was right :). Glad it's fixed.
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Me too! Thanks for the help!
 
Anyone have a pic of this seal between Master and Booster? There's not one on my car, nor my parts car

Does Gen1 use this seal? Maybe I can snag a couple from the JY if so
 
I wonder where mine went then. Grr
I stuck the biggest o-ring that I have in there, but its not quite big enough, I'll have to find one from somewhere
 
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