I replaced the half shafts on both sides. After doing this the left side half shaft pulled out about 20 miles in. I have put it back in but after I put it back in I gave it a light pull and it comes back out with very little effort. It does seem to click a little before it comes out, but it does not take much effort at all. That does not seem right. It took a tremendous amount of effort to get the old shaft out. I am worried that if I just put this back together it is just going to pop out again. It seems to me that maybe the snap ring is not correctly engaging. Should it be that easy to pull the shaft back out immediately after putting it in? BTW this is an 04 R53 with the 6 speed.

Edit: I mean left (driver) side. I was so frustrated last night I put the wrong side in when I typed this up :( The right side is fine.

 

The passenger side axle doesn't have any snap ring holding it in. I'd verify that you have the correct axle. Depending on Trans, and model they are all very close but vary in lengths so you could have one that is too short making it not engage and fall out.
Or the bracket that bolts it to the block may not be on the bearing all the way making it not go in the trans all the way.

 

Sorry, I mean left. Was so frustrated last night I typed it wrong. :( I've corrected the text of the message but can't edit the title :( And now the title is edited. Man I feel like such a forum newb and I've been around forums for many years :(

 

Verify the axle length is the same as the old one.

Verify that motor mounts are good.

Verify that lower suspension parts are good.