old master with hydroboost

[camaro427-69]

installed my hydroboost today with my old (not really old but 3 years) 1"bore corvette style master. i made a rod to make up the distance between the booster rod and master hole so that i just didn´t actuate the master when mounted. good so far but when finished i couldn´t get the backs to bleed. if i open the backs it´s just a bit of fluid going back and front and the pedal locks up right in the middle downwards. if i open the fronts bleeding works out normal. the brake line has no kinks or something else and the pressure valve is a brand new PV4 for disc brakes. i removed all lines and when i pressed down the pedal the front of the master started spraying fluid instantly but the back just a little bit dripping down. could it be that the old masters are not compatible with the hydroboost systems?????

thanks
pat