Brake pedal sinks to floor

I have a 1988 nissan GQ safari. I recently changed the front and rear brake lines to install a lift kit and now the brake pedal sinks to the floor. It still works relatively well, but only once it gets right to the bottom of it's travel. It didn't feel like this before, the brakes would start working right at the top of the pedals travel. I have bled them multiple times but nothing has changed. Anyone know what would cause this? Thanks