Sounds like booster rod is not coming out far enough to hit master cylinder when installed on booster or is coming out to far and not returning enough to allow for next stroke check with out master cylinder installed to see if the rod is moving when you put your foot on brake petal l believe there is a adjustment on rod.also when you install master make sure that it is not hard to bolt master cylinder to booster and you have a little free play but not to much that there is not enough stroke to push master.hope.l was of help.