LST Diffs problem - Need help asap!

A few weeks ago I asked why my LST only runned backwards, that was because the diffs where flipped. (The top was pointed to the ground) I thought Linc gave me the answer. (thank you!)
But now I wanted to flip the diffs like they have to be. So with "TOP" to the top and not to the bottom. But I'm doing something wrong but I don't know what. I can't push the diff far enough through a circle thingy, and so I can't go further. My English isn't very good so I've also made some pictures:




I read the manual 50 times and I can't see what I'm doing wrong. But the strange thing also is, if I flip the diff (with "TOP" pointing to the bottom) it's fit perfectly!


Please help me, I'm getting crazy!