Drive belt falls off mower

Leave aside all the puffery about 3-1 and such, you described a front wheel drive (pull) walk-behind (FWD), but are asking why the rear wheels won't propel. When you push down the hand grip the front wheels should spin free. Whan you lower from wheels by releasing pressure on hand grips, turning wheels lowered to ground should propel the mower along with its unpowered rear wheels now turning be ground contact. Reminder, never, ever lift rear drive wheels of any mower off the ground while walking behind with engine running:

1. You could be struck by blade propelled object.
2. You could pull mower and spinning blade backward onto your feet.
3. You could lose balance and be pulled forward in a fall.

Contemporary FWD mowers are recognized by a black chain housing on deck top leading from engine to left front of deck. RWD propelling chains are situated underneath deck so cannot be seen from above.

Drive belt Ok?

Drive cable or drive belt could have broken

Cable could be stretched belt could be worn or old, if it has a gear box maybe it slipped a gear or lost some teeth. Do some investigation, Good Luck

remove the front black plastic plate that is stamped self propelled and replace the wheel drive belt that attaches the engine pulley (above blade) to the transmission pulley (found under the cover). When you buy the belts, pick up two or three as I seem to go through a couple per season. Hopes this helps

Typically self-propelled mowers are propelled using the front wheels, which only turn forward. Pulling the mower back while the front wheels are turning will damage the drive gears. It's best to raise the front wheels slightly off the ground before pulling back.

ya the trans is trying to go out and thay look up thay do that all the time

remove one wheel to expose the belt ,

put oil or grease all the shafts and bearings inside and out, if possible adjust the cutter blade contacts.

You turn the mower over, remove the blade with a 9/16 or 5/8 socket. There is a bolt holding shroud on, 3/8 or 7/16, there are two screws by the rear wheels, 7/16 that need to be removed. Once the shroud is removed, belt can be removed and new one put on.