there is two things that could cause the hst pedal to be limp. as others said the rod link from pedal to the rear connects to a plate that the hydraulic rams must have come off from the cotter tee that fell out. well.. the cotter tee is wrong term as kubota has there own spring clip thing , but concept is the same . needs a pin to hold the rod in. you really need to have the mower deck off to see as its your first time under there to understand the workings. the other possible is the adjustable nut that holds the spring down on the hst but still part of the link but not the rod must have came off which is impossible since its a locking nylon nut. again- the mower deck needs to be off to see things better. i am willing to bet im 99 percent sure its a linkage issue somewhere and getting the deck off is the first step.