I viewed a parts diagram at www.arcolawn.com and your machine is equipped with a shifter under the battery in the back. If the shifter is loose to shift the ball socket of the ball joint that attaches the shifter to the transmission is broken. If you can hear the gears shift but the unit will not move it is a problem inside the transmisson. I recommend checking out the parts drawing at www.arcolawn.com you can get what you need super fast.
Thank you

Joe

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