Hi, what master cylinders are you using for your cars? I fitted sierra master cylinder, but now having troubles. Then it is empty it pushes till the end, but then it is filled with fluid it pushes half of distance easily and then suddenly stops. what can it be?
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Hopefully not stating the obvious, but sounds like air in the system to me - have you bled the system?

i had to crack open the fittings (where the brake pipes fit) on my master cylinder with someone hold pressure on the pedal
then they all bled up ok
HTH