so i was driving my truck home from work and when i tried to stop only the rear brakes worked (they locked up) and the pedal went all the way to the floor. ive found a leak but im not sure what the part is called..the brake master cylinder attatches to it..it looks like a big bowl that is placed on the firewall.. any help is greatly appreciated thanks guys.
oh yea its a 1986 ford f250 diesle..

 

Seems like you are talking about the brake booster. It is not connected to the brake fluid system. If there is fluid around it then it must be the master cylinder that is leaking and you will need to replace it. If you do replace it make sure you follow the instructions with the new one and bench bleed it.
Just disconnect the pipe connections, undo the two nuts holding it on to the booster and pull it forward and off.

 

Make sure you follow all the installation instructions...especially the ones about bleeding the master cylinder, when you install the new unit...