series 3 axels convison to 200 tdi brake problem

hi i have fit 200tdi axels and am having problems geting pressure i still have the standerd series 3 master cylinder and was think that it can put anothe pressure in the system and that i will need a sevo does any one agree with thiss i am get slight pressure when i put fluid in the system and it holds there and also check all conections and pipes for holes which there are none but this is lost whene open bleed niples and can only get this back by draing the entire system f fluid

your gonna have to put a defender or series servo assisted brake master cylinder on to get enough pressure for the disc calipers as there not enough guts in the old cylinder type servo

thank you i was think it but wanted a second opnion