420 crawler stuck in first gear

[justjd420]

Have a JD 420 crawler. My father had just finished plowing with a two bottom plow when the tractor stuck in first gear. It stuck, according to my dad, while no load was being placed on the machine. I believe my dad may have accidently shifted into first instead of thrid to move the plow to another lot. The shift lever is not locked into first gear and only semi moves a bit. Tried to apply up and down pressure on the lever but it doesn't feel like it is able to disengage the gear. Any suggestions???? Can the lever cover on the gear box be removed to disengage the gears manualy?

[boler76]

yes take top off

[justjd420]

But why does it happen to get stuck?