Just a tip.... sometimes you need to 'prime' the master cylinder

what I mean is that sometimes you can fill the reservoirs but the fluid does not get into the master -especially for the rears (front part of the master)

I got an old brake line and bent it so I could squeeze some fluid from up underneath and filled the reservoir through the system (thus guaranteeing that there were no air locks in the master).

then replaced the brake lines as normal and bled the system

I hope you can follow what I am talking about