My Brakes Aren't Bleeding

Jetsetter

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So I installed Cobra brakes, rotors, and lines. I bled using the buddy system, with my friend pumping the pedal, another friend pouring fluid into the master, and my opening and closing the bleed valves. My friend pumps the pedal until all the air is bled out and the pedal feels fine, just like it did before I took it in for work. However, the second I turn it on the pedal loses pressure and doesn't return. I then rebleed it, pedal feels fine, and it dies again when its turned on. WTF? Do I need to bleed the brakes with the car running? Is there something I'm missing here?
 
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Jetsetter

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With no help from this forum I was able to get help bleeding it. Since our cars have a vacuum assisted hydraulic brake booster, the car has to be running to bleed it. I highly recommend getting a clear plastic tube and slipping it over the bleeder as it shows you if you have air in the lines.
 

El_Diablo

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i dont know who told you the car has to be running but it doesn't.......

were you bleeding in the correct order? new master cylinder? there will be a lot of fluid to go through until you get new components bled, i usually keep 2 quarts minimum handy for bleeding the entire system
 
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Jetsetter

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It most definately had to be running to bleed mine. It was new calipers, nothing else. Also bled in the correct order.

The brake booster is ran by the vacuum system so the engine has to be going to get the booster to bleed.
 

BigTang

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there are other issues if you need to have the car running to bleed it.

There is probably air trapped somewhere in the system. when I install calipers I typically let it gravity bleed while I take a break for a while. Just top off the master cylinder, open up the bleeders and sit back for a while. there will be fluid on the ground and just close the screws, top off the master cylinder and check the pressure. manually bleed if needed.
 

cntchds

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If you only replace the front calipers do you have to bleed all of the brakes, or just the ones you replaced? Sorry if this is a stupid question.
 

BigTang

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Just the end you replaced as long as you didn't mess w/ the master cylinder.
 

95mustang_gt

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BigTang said:
Just the end you replaced as long as you didn't mess w/ the master cylinder.
cntchds said:
If you only replace the front calipers do you have to bleed all of the brakes, or just the ones you replaced? Sorry if this is a stupid question.

just the fronts usually but sometimes you want to bleed all four.And when you do bleed you want to start from the caliper furthest from the master cylinder.So it would be RF,LF,and if you did all 4 corners it would be RR,LR,RF,LF.

to the op the car does not need to be running.It takes time to bleed the brake system and if you let it get a lot of air you should do all 4 corners.
 

x182dan

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ya man you dont have to have the car running i didnt when i did the caliper swap
 
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Jetsetter

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I bled the car 4 times with the car off and every time I turned it on the pedal died. I bled it with the car running once and have normal braking now. I used almost the exact same procedure the first times as the last, the exception being the plastic tube.
 

x182dan

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I had a similiar problem like your saying. I bled them and the pedal felt mint, then I drove it and I could barely stop, I had to pump the shit outta it to get it to stop the car. I came back home bled it again, got some more air to come out of the calipers. I did do all four calipers because the back ones were junk and they wouldn't even turn in.
 

Win

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Yeah you don't have to have the car on to bleed the brakes. I have never done it and every ASE tech or Master Tech i worked with has never had to. I usually just use a speed bleeder hooked up to a air line.
 

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