ldv brakes?

i have two convoys and with both i cant get any brake pedal for long i bleed them the pedal goes hard and a couple miles up the road it goes again im not loosing any fluid and all the pipes and cylinders are dry also on one i cant get any hand brake ive stripped both drums and freed everything up and replaced both slave cylinders and the handbrake splitter cable wich was seized and still no joy the other truck isnt very good either also in south cornwall any one recomend a good mot test station as ive been screwed by three already failing me on new tyres and making stuff up any help would be greatly apreceated