Pedal goes to floor

OK, vehicle is an 80 Crew Cab, a few years ago I put on a rebuilt master cylinder. Well the rear wheel cylinder are leaking so, I have replaced them, have not yet added any brake fluid to the smaller front section of the divided master cylinder (the side that feeds the rear wheel cylinders) without the fluid added the brake pedal goes all the way to the floor, even though there is no fluid in the smaller front section the bigger rear reservoir is almost full (it feeds the front calipers) question is, should the pedal not bee off the floor somewhat because the rear side (front disc. side) is still working?

Thank You!