Won't Shift Into Gear While Running

Whoa!
If the departure goes from enough to not enough as the pedal goes down, and then the disc tightens up again with the pedal on the floor; that kindof speaks to a bent or warped or somehow damaged disc. Meh, maybe not.
The Zbar tube is sitting parallel to the floor and at 90* to the vehicle centerline,right? And is positively located by that special clip,right?;so that the bar cannot move back and forth on the pivot balls,right? And the pivot balls are similarly positively located,right? If the bar shifts, some pedal-motion will be lost,as the linkage will, as Phreakish says;"re-engineer " itself.