Not building brake pressure?

[RockcrawlerEX]

This just happened today. I press my brake pedal down, and it doesn't build pressure. It sounds like its losing pressure as the brake pedal goes down. Then all of a sudden it'll brake completely. I wanna say it's the booster, but I haven't really had experience with brake failures. Can someone help me out? I have a week to fix it, thankfully it failed at the start of my thanksgiving break.
[edit] Now with video.

http://www.youtube.com/watch?v=oRgTmI_hsro

And sorry about the super loud door chime. I didn't think it'd come out that intense lol

 

[RockcrawlerEX]

Oh, and my fluid level has gone down a tiny bit. Could it benpossible my pad fell off the caliper?

 

[waskly]

check brake calipers, and for leaks.

 

[RockcrawlerEX]

I don't think it's a leak, it hasn't lost that much fluid and it started doing this like at 2.
But that's what I'm thinking is that a pad or something fell or broke and it's having to compensate for it. But it's too dark to tell right now. I was just wondering if my suspicions could be right.

Edit
Read your post wrong. What could be wrong with the calipers? I moved the truck and there wasn't any fluid on the floor or anything.

 

[waskly]

brake leaks might not cause puddles like a coolant or trans leak, i would look under the truck at each caliper to see if they are wet, they could be leaking.

 

[ragajungle]

is the pedal hard? If so you might have a bad brake booster or a vac leak to the booster. if not the calipers or drum issue it could be the master cylinder gone bad.

 

[shaggymane]

It would be helpfull to know if they *pump up*. What happens if you step on the brake a second & third time? Does the pedal get hard closer to the top? If they do pump up I'd suggest pulling the rear drums to see if the self adjusters are intact and working.

While they are off it would also be apparent if a wheel cylinder is leaking

If the pedal continues to fall to the floor each time it's pressed down, the master cyl is a good bet.

Never dealt with a bad booster before. But I'd think it'd be about like braking with the engine off. Is it the same?

So people..... how is a bad vac booster tested?

 

[RockcrawlerEX]

is the pedal hard? If so you might have a bad brake booster or a vac leak to the booster. if not the calipers or drum issue it could be the master cylinder gone bad.

Well that's what I mean. Instead of the pedal getting hard, it slowly goes soft, then my brakes kick in completely.

 

[RockcrawlerEX]

It would be helpfull to know if they *pump up*. What happens if you step on the brake a second & third time? Does the pedal get hard closer to the top? If they do pump up I'd suggest pulling the rear drums to see if the self adjusters are intact and working.

While they are off it would also be apparent if a wheel cylinder is leaking

If the pedal continues to fall to the floor each time it's pressed down, the master cyl is a good bet.

Never dealt with a bad booster before. But I'd think it'd be about like braking with the engine off. Is it the same?

So people..... how is a bad vac booster tested?

No, my pedal doesn't pump up. That's why I said it's not building pressure. And yeah, it's still the same if I brake while the engine is off.

 

[FIND]

can you see any brake fluid leaking out around the flange on the master cylinder where it bolts to the booster? It may be very slight. Anyways, first check all 4 wheel brakes, if they all look good, your problem is probably in your master cylinder.

From the sound of it, your master cylinder is most likely bad. It can be bad without leaking out to the outside too, just so you know.

 

[swetrid]

Brake booster failure will result in hard brake pedal and no assist. It will not cause low pedal. Could be master cylinder or RABS valve along with any external leak concern(wheel cylinder,caliper,lines).

 

[RockcrawlerEX]

Scratch what I said about it not stiffening up hen the engine is off. It builds pressure with it off, so that should mean my booster is fine, correct?

And so far it looks like the pads are still on the calipers and I don't see any leaks on them, but I don't have a jack that lifts the explorer, so I'm not 100% sure they're not leaking. Theres a wet spot around the top of the mastercylider, around where the cap goes.

 

[RockcrawlerEX]

Bump. Added a video.

 

[MudRunner90]

does it pull to one side when you are driving? if it does then there could be air in the line or, that brake line could be leaking on the side that is not pulling. i had to replace a line on one side i think it was like $15 but hat may have been the power stearing line, idk but it should be some where around there

it wont puddle up it will just spray all over when u push on the brake.

ether way try to bleed the brakes, there is a small valve on the caliper, just lossen that and have someone push the brakes till there is no air just brake fluid.

if that is not it i don't know what it would be.