Series 3 brake problems

Hi all im new to the 4x4 scene and have acquired a series 3 SWB cheap of a friend.
Have started doing the required restoration work which has included a full break overhaul.The drums were ok so i have replace all wheel cylinders and shoes, new seal kit in the master cylinder as the cylinder bore looked and felt ok,and new hoses. The brakes have bled fine to each corner expelling all air. However when the pedal is pushed for the first time it goes to the floor but then gets better the more its pushed, until you leave it for a few second then its the same again. All shoes ar adjusted correctly, there are no leaks and all shoe springs are fitted correct and are fine it is also the same when the engine is running any help would be much appreciated

cheers dom

Sounds like trapped air,Take cap of resevoir and use a piece of wood or pipe and wedge pedal down and leave overnight.under this constant pressure any trapped air will come to top and when you let pedal up it should be solid

fit new master cylinder