I agree, I don't think it is the ACR. It sounds like the trunion is worn and/or neutral is off of center. Read through the link Maxwell (cub cadet 123) listed and perform any repairs needed to the trunion. Then reinstall the drive shaft and start the tractor. You may have to move the hydro lever as you crank to find the spot where it is not loading the engine and allows it to start. Then follow these instructions on adjusting the neutral position.
http://cubfaq.com/neutraladjust.html
Bill