Not sure what is chattering but have had RWD mowers where the inner teeth on the wheel were worn such that after reversing manually(pulling backwards), they would not engage properly when trying to move forward. The teeth on the gears inside the gearbox are spring loaded from memory, and have no guaranty of good engagement. I would check the mesh of the drive gears to the inner gears of the wheels.
tom
UPDATE: After replacing the pinion gears, it started to balk at rolling forward OR backward - "chattering" when the drive was engaged with the paddles, and intermittently locking up rolling backward and eventually forward, as well. Suddenly, everything stopped - no chatter, and NO drive engagement... becoming in essence a "push mower", which STILL locked up on occasion in either direction.
Pulled the rear wheels this afternoon (to determine the extent of parts needed to repair), and both pinion gears/circlips/washers/transmission axle rod ratchet keys/springs were all off and jumbled within the wheels.
I surmise the transmission axle bushings must've finally seized and blown everything apart?
Planning to order new transmission, rear wheels, pinion gears, all springs/washers/key/bushings, and the rear shield (which is partially torn)
Recommendations for the best pricing, anyone?
So far, I've come up with $220.45 (including shipping, no sales tax)...
Thank you!
Steve