which case is it:
http://www.amainhobbies.com/product_...ion-Case-B4-T4
http://www.amainhobbies.com/product_...nsmission-Case
One is meant for the gear diff and one is not. I dont think the old case will even work with a gear diff but just checking. Other than that, maybe the top shaft needs to be replaced, does it have the top shaft spacer on it?