Here's my take on your problem. I've seen this problem several times. The rod between the M/C and booster is too long. You need to adjust the rod with the ball exiting the booster. Just behind the ball you should find a nut which, when locked down, keeps the output rod or shaft from getting longer or shorter. That shaft is threadrd so you can make it longer or shorter. There is a special tool for this adjustment (cost less than ten bucks). The tool looks like a "H" with a rod through the center section. There should be about 0.020" gap between the booster rod and the M/C rod.
