Mate take a chill pill and time out. Back brakes are easy, 1. Are the pads closing when you put the pedal down?. 2 Have you tightened all bots associated with what you have changed over?. 3 Bleed, take a rest and bleed some more, n the end you might find that you have a shit load of air in the lines and it is taking longer to clear it. Mate in the long run it takes a lot of effort and TIME...... Have abeer , coffee, tea or what ever but have a brake and enjoy working on the bike.

2C worth coz I have been there heaps of times

PPS just a thought maybe you have a shit piston assy? especially if it going to the floor after a couple of minutes.  If no loss of fluid the  you have a leak past the piston...... Basically she crap and you need a new one. 

 

Just anthought

 

AJ

DNA Forwards, theres your problem

Mate have you tried a reverse bleed?

LOL at Walka

Reverse bleed ?
Interesting
Do tell

Got a set of DNA forwards off a mate for my 89 Heritage, could not get any pressure at all. Tried every way of bleeding known to man.
Got a rebuild kit and fixed the problem.