2000 Kia Sephia Axle replacement problem

Drive Train Axles Bearings problem
2000 Kia Sephia Front Wheel Drive Automatic

So I removed the Dside cv axle and checked to make sure the replacement was of correct size and all. When I put the new axle into the transaxle it just slides right in and doesnt click into place or anything (I have replaced axles before). When you turn the drive shaft it just keeps turning in either direction without resistance. I thought maybe its something kia does so I put it all back together and take it off the stands start it up and put it into gear which it made a loud chunking noise (yikes). And it wont go either forward or reverse.(Obviously splines aren't fitted into the gears) I talked to a kia mechanic and he said I might have dropped a gear. I dont believe that since its a stationary gear in the tansaxle. ANY HELP WOULD BE MUCH APPRECIATED PLEASE>>>>>