I have a 14 year old Yard-Man 21" Self-Propelled mower, Model #12A-979L401 that has become hard to pull backwards when mowing under trees etc. It appears the rear wheels stay engaged with the transmission and therefore it takes more effort to pull it backwards. It seems to me the rear wheels should disengage and free wheel much like the front wheels when pulling the mower backwards. Any suggestions and/or comments appreciated.