FRUSTRATED! need help with carrier swap

8.75 rear, ok so i changed out my carrier 489 case 323 mini spool for a 489 case 3.55 cone type suregrip unit. the problem im having is the driver side axle shaft wont go in all the way i hit something when its about a half a inch from being in completely. my question is where did i go wrong? do i need to shorten the axle shaft or what/ im stump! the driver side can go in all the way and bolt right up no problems. thanks in advance:newb: