Cherokee 140. While trying to trim up practicing slow flight and steep turns, based on the overhead indicator the trim is stopping early while adjusting it. I hits a definitive stop and does not give suspicion that it can be forced past this point. I have approximately 2 more has marks on the indicator above my head. I am not completely familiar with this aircraft, would this indicate that the cable may have not been "calibrated" correctly or its upper and lower limits are not correct? Thanks in advance, you guys are awesome.