Front Brake Issues

Hi, I could do with some advice. I have a thunderbird 900 with a front brake problem. I have no resistance in the brake leaver. I have change the seals and bleed nipple in the caliper, changed everything in the master cylinder system, but this dose not seemed to have worked. Everytime I try to bleed the brake fluid through nothing happens, the nipple also seems to be suckling air back in, but it's not the nipple itself as I have tried it with the old and new nipple, same happened with both. Any ideas?