Left Hand Recessed Door Offset Pivot Set, 79-123 too short.

I have installed the 79-123 commercial door pivots many times in the past. Once installed and adjusted, I have never had this problem. I'm not sure why you're having this issue. A few things come to mind: first, make sure the top spring loaded door pivot pin is completely extended at the top, so that it goes into the top pivot in the frame header. At the bottom pivot you have two adjustments, one is the hex bolt pivot in the bottom threshold pivot, and the other is the bottom door pivot. It has a cover screw that, when it is removed, will expose the allen wrench adjustment screw. Turning the screw will help raise or lower the door. My last thought is that you should make sure the 79-123 is identical to the original pivot. If there is even a subtle difference, it could be incompatible with your door.