Drive shaft df 2.5

[Marco64]

When I put my df 2.5 in to gear the drive shaft slips and the prop only engages in jerks. The problem started when I changed the impeller which i did without removing the leg. The problem seems to be with the top of the drive shaft. I have seen some manuals where there is a bush at the top of the shaft but there is nothing on mine now. Any advice appreciated !

[boats.net]

The shift rod may not be aligned properly in gearcase.