Small Engines (Lawn Mowers, etc.): Craftsman self propelled mower, pulley, craftsman

Question
Craftsman self-propelled mower Model #917.378680...When engaging self-propelled feature, it does not engage the front wheels.  The pulley spins fine, but when pushing on the lever, it does not engage the system.  The cable is tight and lever is working fine.  But the pulley just spins.  How do I go about repairing this problem?  

Answer
 Hello Dale:

 You say the pulley just spins. Is the pulley spinning on the shaft or is the shaft Turning too.  If the Shaft is turning then the Gear Box has something busted inside. If not then the Key has sheared. Remove the pulley and replace the Key.  Hope this Helps.

 Good Luck

 Respectfully

 John