2004 Mercury 90 hp - How do I get reverse to work after reinstalling my lower unit?

by Al
(Janecko)

I changed my impeller on my 2004 Mercury 90 hp ELPTO, when I installed to lower unit, I can't get my prop to move in reverse, it works in forward and neutral and I've tried every spline position in the gear linkage.
What can I do to get into reverse that I haven't tried already?

Thanks Al