Have an older Deere JS20 self propelled rear wheel drive mover. Been a great mower until this year. My problem is that when you try to make a sharp turn the rear wheels don't always want to disengage. It getting worse everytime I use it. If you try to turn sharply on pavement, one wheel turns foreward and the other trys to spin backward. On turf it can be bad enough to rut the turf. Yes I'm letting go of the drive control lever when I turn the mower. Any thoughts?