brake help

[canonball]

I recently purchased a '66 lwb C20 fleetside. Everything runs pretty good, i've changed the coolant, oil, oil filter and bought new spark plugs and wires and an air filter that are gonna go in soon. the biggest issue right now are the brakes.

the story: When I first got the truck there was a tiny bit of stopping power in the brakes. There was fluid in the resiviour and the pedal wouldn't go to the floor, there was a lot of resistance and it did very little to stop the truck. I drove it in some light rain and wet roads one day and since then when I push the brake pedal it goes straight to the floor with no resistance and no stopping. After checking the brake resiviour again I found no fluid in there, so I refilled it and the brake pedal still has no resistance and goes all the way in.

I've got a mechanic friend that is going to take a look at the brakes for me after I disassemble them for him. I just wondered if anyone had any theories about what's causing the brakes to fail and any suggestions/tips for taking the brakes apart. I'm not looking to do a disc brake swap at the moment, money is tight right now. Besides the brakes and a lot of play in the steering rack this truck is road ready and my only transportation so I need to get it on the road. Thanks!