Transmission rebuild. K2 drum stuck

[arvsreyes]

Hi, I'm in the process of rebuilding my transmission. I'm about to put it back. But when I tighten the collar nut (at the back of the transmission), the K2 drum (K2 carrier) gets stuck and does not want to spin when the planetary gear set is turned. (when the collar nut is still loose, the K2 still spins together with the planetary gear set)

I also removed the other parts already (gear pump, servo, brake band) and only the planetary gear set and K2 are attached

Note, I replaced the K2 drum also as the original one had its central top outer shim detached

Car is 1987 w124 300d turbo
transmission 722.317

[arvsreyes]

Please see additional pictures for reference

the K2 drum is stuck once the collar nut is tightened. Any ideas? I can't see what's wrong.

Also, can I leave the collar nut not fully tight so that the K2 drum will spin? I'll try to just lock the nut