Sometimes brakes goes to the floor .

Lift the front of your Ford F-250 off of the ground using a jack and jack stands. Remove the wheels from the Ford with a lug nut wrench to prepare the truck for servicing. 2 Open the hood on the engine compartment and take the lid off of the master cylinder that bolts to the brake assister on the driver's side firewall.3 Remove the hex-head bolts on the back of the brake caliper with a socket. With the bolts removed, pull the caliper off of the Ford's brake rotor.4 Pull the old brake pads out of the caliper and discard them. Squeeze the brake piston back into the backside brake caliper with pliers, and then insert the new pads into the brake caliper.5 Pull the rotor cap cover off the middle of the rotor with a screwdriver and use a socket to remove the nut located behind the cover.6 Pull the rotor off of the wheel spindle.7 Remove the old wheel bearings from the brake rotor and insert them into the new rotor. If the old wheel bearings are worn, replace them with new bearings.8 Slide the new rotor onto the wheel spindle and secure it using a bolt and socket. After you tighten the bolt, press the cover back onto the rotor.9 Place the caliper on the rotor and secure it with a socket and hex-head bolts. 10 Duplicate the process on the passenger side of the F-250. 11 Close the master cylinder after putting the wheels back on the Ford and lowering it to the ground. Press on the brake pedal to seat the pads against the rotor
Replace the F-250's Rear Brakes 1 lift the rear of the Ford F-250 off the ground with a jack and jack stands. Remove the wheels from the Ford with a lug nut wrench.2 Place a strip of paint on the back of the brake drum and rear brake drum cover so you can position the brake drum orrectly when you put it back on. If you plan to install new brake drums on your Ford F-250, skip this step. 3 Place the brake drum puller on the brake drum and pull the drum from the wheel hub. The method for attaching the brake drum puller depends on the brake drum puller that you use. 4 Remove the springs that attach the brake shoes to the wheel hub by pulling them off with pliers.5 Lift the old brake shoes off of the wheel hub and place the new brake shoes on the wheel hub. Secure the new shoes with the springs.6 Pound the brake drum onto the axle hub with a rubber mallet.7 Duplicate the process on the passenger side of the Ford.8 Put the wheels back on the F-250, lower it to the ground and, then press on the brake pedal to seat the shoes against the brake drum.

Sounds like your brakes need bled or your vaccuum booster is getting ready to go.

Are the rotors worn? Worn rotors and new pads will sometimes cause this. The pad sits across the ridges and no matter how much you bleed the system the pedal just wont stiffen up. (See diagram. A - New pads, B - Rotor, C - Ridge)
If you did not install new pads you may also want to check the master cylinder seals. First bleed the system at the pipes that connect to the master. If the rotors are ok, you've bled the master cylinder and the problem persists then replace the seals or the complete master cylinder.

SOUNDS LIKE MASTER CYLINDER SEALS ARE GONE. REPLACE MASTER CYLINDER WITH NEW OR REBUILT UNIT.

make sure the rear shoes are manually adjusted up properly ,then is still no good renew the master cylinder because the seal between the front and rear chambers could have gone ,but i do feel that you should manually adjust the rear brakes up properly,slacken handbrake cable before you do this though

adjust your rear shoes up so that the rear drums just turn, with them ajusted to a low setting the brake pedal will be low .
also when you start your engine it is noral for the pedal to drop because of the boster ! [ but not to the floor ]
Bruce Pike

Sounds like air is still in the brake lines, the air sound that you hear is the power assist, but the brake pedal needs to be "high and hard".

if the pedal goes to the floor, that is not good. Sometimes, when pumping brakes for bleeding purposes, the master cylinder gets damaged, as the piston goes past it's normal "travel zone" and gets damged on deposits.....

Now, with that being said, if everything was perfect, brakes are typically not as firm after replacement, due to differences in new pads/shoes and old rotors and drums. Pedal to the floor, however, is never okay.

Doc

Hi I'm litoshop if you bled the system and get no results then your brake pump needs to be replaced now before replacing make sure your pads are installed correctly because if there not this to can cause this problem good luck. if this information has been useful please let us know thank you.

Hello;
The parking brake cables may be stretched and in need of adjustment. Follow the cables along to a nut. Then you can tighten the adjusters up on both sides until you have the proper tension. Also make certain none of the brackets are bent or broken that the cables ride through.
Thanks;
RPM Northwest

are your rear drums set up? why did you bleed the brakes. when only when you installed new pads?