I recently got my 72 240Z and i replaced the old slave cylinder and cleaned the master. Even how hard i try to bleed it, it wont move a bit.

Is the master cylinder pushrod too short or could plain air cause this? I've got another smaller Datsun but it never had problems in there

Lots of discussions on this issue. You can do a search and find a lot of suggestions to get the clutch working. Since their is no bleed on the clutch master try pumping the pedal then loosening the hard line at the master. Bleed the same way as the slave until you get a steady stream of fluid, then move to the slave and bleed it. After bleeding the master in this manner the clutch pedal should be firm or firmer than when you started. Also you might want to take compressed air and with the hard line loose on the master and slave , blow air through the hard line. Could be rust crud in the hard line. You might also want to replace the rubber line going from the hard line to the slave.