So, I need a little help with my brake matter.
A while ago, I noticed that my Brake fluid was low, so I added some, and long and behold, it was my Master Cylinder that had bad or old guts.
So, I bought a certified rebuilt one from Oreily's. As well as a newer Brake Power Booster for a JunkYard. The brakes were working perfectly for the first 3 days, then this morning, the peddle went to the floor. I checked the fluid, and it's full. A buddy of mine told me to check my Check Valve on the Booster. Due to the fact that when I put quick force on the brake pedal I get pressure, but as soon as I let off of it, it goes to the floor...
It seems like, I am not getting enough or no pressure at all... If I had a break in one of my brake lines, then I would be losing fluid... I'm thinking that the check valve has something to do with it.
Any help would be greatly appreciated I have a video of me showing you how easily I can pull the Check Valve from the Booster, but it won't let me load it. My email is Iancrowley467912@gmail.com if you would like to watch it

 

Are you talking the vacuum check valve? Nothing to to with the vacuum will make the pedal fall to the floor.

either the master cylinder is crap, or the rod between the booster and the master is borked.

The power booster is an assist device only it just makes it easier to engage the brakes.

As an experiment what happens if you press in the pedal with the engine shut off?

 

With the engine off, the pedal goes to the floor.. It sinks in.

 

You do a thorough brake bleed on it? Did you get air into the ABS unit when you did the MC install(easy to do if you changed the master)?
If the brakes worked for awhile and then a few days later air got in the lines it COULD be that air in the ABS module finally made it into the lines.

There is a power brake booster check in the Haynes manual I have to determine if the booster is working properly. I don't have it electronic but I'm sure you could google it.

If the pedal is going to the floor at all times(truck on and off) seems like you may have tons of air in there.

I just did a complete brake system service on my car because the pedal went to the floor. I replaced the MC, all pads and rotors, all new calipers, and all new wheel studs while I was there. Presently doing the brake bleed and if it’s slightly spongy still I’ll have to bleed the ABS module. There are scanners you can buy from China for aroind $100 that will do the abs bleed procedure.