Zetor 4718 problem

Can anyone help?

I have an old Zetor 4718, I thought the clutch plate had gone but when I changed it for a new one and put the tractor back together it appears I still had no drive to the gearbox. The pto is driving and disengaing properly but the normal gearbox does not seem to have any drive similar to the clutch been depressed. The clutch appears to be working correctly. Has something come adrift or broken in the gearbox??? Any clues would be most appreciated.

is the rollpin in the hi/lo gearlever apiece ?? it might be broken (or allmost broken) and in neutral.