I would assume you are talking about an MLVW?
I would also assume you bought it at Prefair in Montreal? If you did, I am not surprised. One of the trucks we bought there has break problems. And the other truck needs the breaks adjusted. Most of the trucks he has left are in pretty poor condition.
There could be a ton of different reasons why it is like that. When you say the pedal is on the floor, what do you mean? Do you mean that you push the pedal right to the floor and the truck will not stop? Or is the pedal just sitting on the floor?
Did you check the break fluid reservoir? It is located under the little door, under where the drivers feet sit. Open the door, then unscrew the plug and look to see if there is any fluid left. You will need a flashlight to see the fluid level.
If there is very little to no fluid, you will have to fill it back up, then bleed the breaks on the truck.
Check that first, as it is common on a lot of the MLVW's as most of them have been sitting for a few years in the back of a supply depot with no service done to them.