Installing new 8 3/4 axle shafts

Sorry for the lack of info guys , The axles seemed like they would start to but not fully engage the side gears which would not allow the bearings to enter the housing fully. So i pulled the pumpkin to check how far the new axles went in compared to the old axles = 3/4 " farther with the old axles , The new axles i purchased from DR Diff (cass) which are black nitrate coated ,i don't know whether that was the problem or if it was just a tight fit for the new axle splines. I tapped them in with a mallet and after a few times i got them to fully engage and slide in and out easily!! HOOOOOOORAY !! I'll try it again tommorrow . I'm installing these axle's with a wilwood disc brake set . "THANKS" everyone for the quick response !!