Problem with ball diff T-nut

[AfroP]

Hi

I've been building my 210 up over the bank holiday weekend, taking my time and trying to do it as best as possible.
I got everything built up and followed the diff build guide on the internet.
The circlip is in the right way and has been checked and re-checked
but the problem I'm having is getting the T-nut far enough down to not cause bother with the drive shaft and give it enough space to freely move back and forth

but I cant seem to get the T-nut down far enough

I have compressed the diff spring several times with pliers but still have a problem as you can see from the attached pic

I have checked and double checked that everything is as it should be according to the manual and have rebuilt the diff three times trying to get this sorted.

any body have any suggestions or advice?