I can't fully insert front CV axle into the differential. Can anyone help?

I'm working on replacing my left-hand side CV axle due to a torn boot. However, I'm stuck at actually installing the new axle. It goes in part-way, but won't pop all the way in. I've tried rotating it, I've tried a rubber mallet, but nothing is helping. Any suggestions? Thanks for any help!

 

Make sure the opening on the circlip on the axle is facing down. Seems to make them easier to get in

 

Also a deadblow hammer might be better for hitting on the end. If not that, a small sledge with a block of wood or 2x4 against axle.

 

Curious as to how you've concluded that the CV is not seating fully ?
got some pictures ?

Is this a factory original CV and circlip
or something aftermarket (OEM) ?

OEM is close maybe... but not always the same as the original.

Possibly the circlip is out of spec (larger)...
Or the CV's endshaft is slightly different ?
Did you compare the old CV's end shaft/circlip to the new one ?
Do they look to be the same ?

Possibly yer just not hitting it with enough force
and the new circlip is out of spec slightly
making that more difficult ?

A heavy (soft) deadblow sledgehammer works best.
And can reduce the possibility of CV thread damage.
Sucks if the nut retaining does not turn on easily.

When you say you rotated the CV shaft...
did you also try rotating the diff itself ?
(turn the other side/CV shaft to rotate the diff. slightly)

Pictures usually offer more perception for others observation...
so if you can share those... that could be helpful.