Just finished putting a basket case on the grass again. An older snapper rider, it does every thing fine except back up. Has the typical rubber drive unit under it. this is not the first one that has done the same thing. You must hold the shifter in reverse or it moves out of gear, and it does not have the grab to move the mower if it is trying to back up and incline, it has lots of rubber and the drive plate is not cracked or warped. tried adjuststing the small adjustment to give more pressure between the drive plate and rubber driver.. still the same results. I do not have a manual covering the proper way to adjust .... help if you can... Please.