97 f150 brakes

I had to change the brake pads on my truck, and now i am in the bleeding process. we have bled the brakes for 3 days now "not joking either" and i am not getting pressure on my brakes while the truck is running. when the truck is off, the pedal is hard as can be, but as soon as i turn the truck on, the pedal goes straight to the floor. We have tried numerous things but still can't fix it. if anyone has ideas, i will gladly try it.

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Did you have a firm pedal before you put the pads on it? What all did you do/replace when you put the pads on, calipers, wheel cysl..ect? What method are you using to bleed them? You say "we", i assume you have someone pumping the pedal, and someone underneath working the bleeders. Make sure the person pumping the pedal isnt letting up on the pedal before the person underneath closes the bleeder, and make sure the person underneath is closing the bleeder before the pedal is released. I like to bleed them by myself for that reason. You can buy a self bleeder kit pretty cheap, or make one with some vinyl tubing and a plastic jug/bottle. Get some tubing that fits snugly over the bleeder(i use vinyl so i can see the fluid and bubbles) , run it to your container and watch till the fluid is clear. I like to hang the jug on a stand above the fenders where i can see it, also the pressure from the fluid keeps air from being drawn back in around the bleeder screw threads.(line in the bottom of the jug, soft drink bottle with the bottom cut out, drill a hole in the cap that the line fits in snugly) Pump several times till the fluid is clear, and on the last pump let the pedal up slowly to make sure no air is drawn back in. Do this till the fluid is clear with no bubbles. Also watch the master cylinder to make sure it doesnt run low on fluid, keep it filled. Start with the longest line on the rear, and only try to do one wheel at a time.

yes, there are 2 people, and we have good comunication when bleeding the brakes. i don't let go on the brakes till he gets up and says it's ok, so we don't get any air back in the brakes. the pressure was fine before we changed the brakes. we were going to replace the one calibure because it not unlocking, but we got that working and seems to be fine now. we did not replace anything else, just the brakes. i took off the master cylinder to make sure it wasn't leaking at all. seems fine. we took the calibures back off and put brake fluid back in through the brake line. we even let it sit for 2 days to let it the air bubbles seep through. nothing seems to be working though.

Ok, when you had the calipers off, did you plug the lines where the master cylinder could not drip dry? When you say you took the master cyl off to check for leaks, did you take the brake lines loose, did the master cyl ever run out of fluid?? If so , i would take it off and bench bleed it. You can do it with it on the vehicle, but its simpler with it off and in a vise and it only takes a few minutes to get it off. You definitely have air in the system, and if the master cyl ran dry it almost impossible to get all the air out doing what youre doing. Bench bleed it and start over, youll save alot of time aggrevation, and brake fluid.

the master cylinder did not completely run dry, but i too think it's just air. it's getting very frusterating though. I'll try to bench bleed them when it cools down and hopefully that will work. i'll let you know one way or the other. thanks.