AX-15 1st gear wont stay in

Hi all, long time lurker, don't post much, TIA for hearing me out.

This is my second XJ with the AX-15 and I have searched for quite a while and can't find any solid solution or suggestion on how to fix this problem.

Every other gear works as it should and holds strong except for 1st. I can shift it into 1st with no issues and as soon as I hit the gas it will strongly pop out with a bang.

I read it might be low on fluid so I did a fluid change today with Redline MTL and made no difference. Also being cold or hot makes no difference.

Any ideas what I might look at next?

Might look at a rebuild....mine did the same thing right after i had it rebuilt and i called to complain...they pulled it apart right there and it had a bad 1-2 syncro....after some complaining (the nice way LoL) i got my money back and they paid to have it rebuilt at a more reputible shop....No problems going on 5 years now

Yep, I think your right. After some more research I am going to do a master rebuild and see what happens... should learn a lot!