Can anyone tell me the piston push rod free play from the maximum off position to when the initial pressure starts? I have talked with tech support at Crown but they do not have this info. What I was told was they send an original unit (presumably Wagner in this case) out (overseas) to be duplicated and they have no drawings or specifications sheets to refer to. This is the dual master cylinder for 10" drum brakes on 66-71 CJ5 & 6. Thank you.