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My Craftsman s/p mower model #917.378480 power-propelled drive was not working.
Upon examination the drive cable and belt seemed to be functioning properly. I took the transmission case apart to discover that the helical gear teeth were worn into a cupped shape so the worm gear was not engaging the helical gear and slipping resulting in the no go. I could see this happening on a plastic gear but this was steel as evidenced by the attached pictures. I had to remove the axle shaft in order to slide the gear off the axle and replace it with the new gear. :frown:
I had some difficulty getting the axle bearings off the axle as I had been a little to aggressive trying to hammer the axle out and had flared the axle ends and compressed the D-clip grooves a little. I had to grind the ends of the axle a little to get the bearings to slide off the end of the axle. :mur:
This also resulted in the D-clips being difficult to reinstall to hold everything on the axle. So if you attempt this repair go easy on the axle shaft ends. Got it all back together and mower is functioning properly now. :cool2: Total cost of repair was $7 for the new gear.

Those gears are not solid steel, but a softer steel alloy. Steel would be too heavy. They do wear that way, mostly due to a very, very, very cheap grease used in the unit.

Rivets said:

Those gears are not solid steel, but a softer steel alloy. Steel would be too heavy. They do wear that way, mostly due to a very, very, very cheap grease used in the unit.

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Thanks for the information, Rivets. I did not have or use the type grease that was listed on the parts list for reassembly, instead I packed the transmission with high temperature wheel bearing grease that I had on hand, hoping that will suffice.

That should work fine.