brake problem

i was at prarie city yesterday and when i was leaving my brakes just kinda stopped working. i had pressure to a certain point. so i took it home and realized my wheel cylinders were shot and leaking really bad so i replaced them and that helped but not completley. i can load on the brakes and it will slow down or stop my truck but once im slowed down all the pressure goes away and i have the brakes to the floor and im still rolling. Its probably the master cylinder but i just wanted to ask everyone to make sure so i dont start replacing things that i dont need to be replacing

You didn't mention so I have to ask. You did bleed the air out of the system after you replaced the wheel cylinders right?. And if they were leaking really bad then I would suggest replacing the rear shoes also. Any time you get brake fluid on the shoes they get eaten by the fluid and get real soft and fail. If the master lets the pedal slowly sink to the floor then yes most likely the seals on the inside are bad and leaking internally. If it gets real bad it can ruin the booster by leaking the fluid into the booster and destroying the diaphram(sp) inside. e that helps enjoy
Jay