Hi guys. It seems that the gearbox is stuck in a gear. It is still just a chassis with no engine, but if you push it around, you can hear it runs in gear. I tried to get it out of gear, but it does not want to. The selector rod moves freely, but it feels like it is stuck in a gear.

Please help.....

The gearbox internals do turn when it is in neutral, try turning the output shaft with the wheels on the ground (as your able to push it around) does it want to move the chassis or does it turn freely?

H

It wants to move the chassis.

Does the gearstick feel like its selecting a gear when moved? Is it adjusted correctly?

easy way is to try and turn the input shaft by hand in neutral. if it does not turn tunnel rear plate off and operate the gear lever whilst looking at the selector linkage it may just be a loose grub screw on the selector input ( they should be lockwired )or a worn bush.
a broken failed rod front support bush by the lever gives excess play but still allows neutral selection ok.