So my break bleed kit arrived this morning, first I gave the flip the break leaver level and bounce the bike on it back wheel and screw the small shimano pot in and pump the break, didn’t see a great deal of bubbles to be fair, then did a refill (slowly) flicking and pinging the cables to move the bubbles on, however the break is working but doesn’t feel as firm/hard as it did or the front break does, I’ve now balanced the front wheel up near vertical to see if that helps, not sure what else I can try?
I have had good success with the following but if it doesn't work I would do a full bleed from the calliper.
1. Wind the lever reach all the way out as far as you can from the bar
2. Compress the lever quite firmly and use a bit of material or a cable tie to lock that down to the bar.
3. Prop the bike up in a position where the lever is as high above the calliper as possible. Rear calliper stand the bike up on the rear wheel, front is fine just standing on both wheels.
4. Leave for a few hours.
If possible, try to do the next step in the same position i.e. standing on rear wheel for rear calliper. This should migrate most/all of the air bubbles to the lever end.
Then do the standard "lazy" brake bleed. Lever parallel to floor, screw on bleed cup, small amount of oil in cup and pump lever lots and keep changing the angle of the bike is you do this to encourage the last bubbles out.
If that doesn't work, you need to do a full bleed from the calliper.