iput gear lt230

Hi there... My old transfer box decided to implode recently, luckily i found a good second hand one quickly! Sadly for me the input gear was missing teeth so I ordered a new cross drilled one. Once the transfer box was eventually back on i tried fitting the input gear ( advised to to it this way as easier to wiggle box onto the studs). The problem i have is the input gear only goes three quarters of the way in...admittedly the chassis mount isn't bolted and there's still one bolt to go into gear box, but can't see how that would stop it that short...any ideas people?!!