[help] Mamiya RB67 coupling arm issue

Looking at the photo Paul posted, it seems like a spring may be loose, broken or tired. The coupling arm is not returning. The arm drives forward with enough force and travel, consistently. It does not return when an opposing force is applied.

Problem solved! (i guess)

It seems that the film back was not tight enough to the revolving adapter, thus forcing the coupling arm to fully extend and getting stuck to the revolving adapter. If you push the coupling arm towards you you may notice that the movement is not linear as one could think. It does a slight curve and i guess that's the reason why it got stuck somewhere around that little hole on the revolving adapter.

I solved this by turning clockwise the screws on the chrome tabs on the revolving adapter until the film back got really tight to it. Before it was quite floppy, now it seems secure and well put. I tried both the motor drive back and the manual pro-sd backs and both work flawlessly with no lost exposures. Try this yourself if you think that could be the cause. I'll keep you updated whenever else might happen.

Thanks for your great help and effort.

Great info, thanks for this thread! Was having this exact problem with my RB and new 6x8 backs.