YS624 and YS828 Friction discs and transmission gears can wear over the years and need replaced. The microfiche picture shows a number of snowblower parts that can be replaced as needed.
Part# 12 is the friction wheel or friction disc in the transmission that drives the snowblower forward.
Part# 28 and part# 33 are transmission gears. If you have difficulty shifting into forward or reverse gears, inspect your snowblower gears for missing, worn or damaged gear teeth.