Pro Jack safety bar.

I have called ProJack and they tell me tighten the pan head screw on the end of the tube. I have tried this. There is a movable slug that can be pushed in or pulled out... Not sure how that works... sometimes the screw will just spin the slug and will never tighten down. My rear jack bar stays up nice always has.. The front has always been loose and i can never get much tension on it... If I can get any tension it is gone after 1 or 2 lifts.
thanks for any help.
Rusty