I know this is a common asked question so I tried everything I could possibly think of before turning to the internet but i have yet to successfully get my brakes to bleed. my bike originally came with no front brakes so the master cylinder is brand new, and the lines and calipers are used, but calipers have been freshly rebuilt installed and the internals are in good condition based on inspection during rebuild. I have also replaced the banjo bolt seals on the caliper with new ones.
bleed master cylinder, bleed lines, then bleed calipers the old fashioned way, push brake, open bleeder, closer bleeder, release brake, repeat. did this for about half an hour to an hour and never got the slightest bit of pressure.
bought the mighty vac kit and proceeded to bleed with vacuum, got bubbles as long as i tried to bleed
let brakes sit over night with brake caliper pushed in hoping any air would release to the top. this seemed to have no effect
removed the master cylinder and calipers from the bike. placed master cylinder on the floor and calibers on the bench. then vacuum bleed, seemed to always get air in the lines. then tried bleed the manual way, fluid seemed to come out clear with no air bubbles. while there is pressure now the lines are extremely squishy and i can pull the brake lever all the way to the bars.
so far i have tried the above attempts at least twice each for the past 3 weeks and im getting pretty frustrated and running out of ideas of what could be wrong.