Small Engines (Lawn Mowers, etc.): Briggs 7.0 Hp- self-propelled ques, external gears, wwii tank

Question
I have a Poulan 21" self-propelled mower that has a rear wheel drive. The rear wheels are not providing any drive-checked wheels-ok, not stripped. Gear and spring seems fine. Right side wheel has drive, left does not. I have replaced wheels, and external gears. Could it be the gear box itself? I need help. Thank you. ps ever read Rising Tide? Great WWII tank scenarios

Answer
You have something sticking in the small gear on the dead  side.  This mower will have a solid axle.  I'm not saying it couldn't happen, but, I've never seen an axle break on a walk behind mower. Pull off the little gear and blast everything with penetrating oil and reassemble.