ORIGINAL: geh3

Remove the gear unit
operate it manually to see where it sticks
NOTE sometimes this does not show up under manual movement
and you might have to use air pressure...
on mine, the problem was the small lip
machined into boyh side rails that provides the''locking''
action for the sliding brass pin. I carefully filed the sharp
points of the lips away so they got less shap and more rounded
this totally cured my problem