mower not driving in slower speed settings

Mtd minirider 76 RDE ride on lawnmower will only move forward or in reverse in the highest speed setting of 6.

Selecting 1 thru 5 either in forward or reverse it just sits there. There is no sound of anything slipping and the fault occurred fairly suddenly not gradually over time

crwdns2934089:0crwdne2934089:0 crwdns2934093:0crwdne2934093:0

crwdns2934109:0crwdne2934109:0

crwdns2889612:0crwdne2889612:0 0
crwdns2934285:0crwdne2934285:0