My 30 year old 7/24 Toro snowblower (Model 38050) won't go forward in 3rd gear. I have tinkered with the friction wheel and can't seem to fix the problem. For example, when the friction wheel is positioned equally from a) the friction disk and b) drive pulley, none of the three Forward gears will engage, but the two Reverse gears work fine. When the friction disk is positioned closer to the drive pulley, all of the Forward gears will engage, but then the 1st gear for Reverse slips badly. The friction wheel seems OK (there is still a good deal of rubber on it). Any idea what is going on?