Sometimes, my self propelled machine feels like it is taking more effort to push and pull-why is that?

The Self Propelled deep cleaner is designed to be used at a slow rate to ensure maximum cleaning results. When you do not wish to use the self propeeled feature, turn the PowerDrive knob to off and proceed at your desired speed. When the machine is not in use, and you are moving it, turn the PowerDrive knob to off. This will allow freer movement of the wheels. For additional information please call Consumer Services toll free at 1-800-263-2535 Monday through Friday from 8 A.M. to 10 P.M. or Saturdays from 9 A.M. to 8 P.M. ET.