:welcome:
To get you in the right frame of mind, you mower does not actually have gears as such.
It is a vari drive with a continiously variable speed.
the selector just holds the speed at a predetermined spot because some find this set up easier to use
It does this by stopping the clutch brake lever moving all the way back up.
Sit on the tractor and put it in 1st, note how high the pedal returns then put it in top and note how far the pedal returns,
Under the mower you will see a stop that is moved by the "gear" lever.
This has come loose or just plain worn down so now it stops nothing.
You wil need to get under the mower and drop the deck to gain access to these mechanisms.
I find it easier too sit the mower upright on its bum after draining the fuel tank and removing the battery both of which can leak