Fat vs. Small shaft sportmasters

[whytey]

I'm having issues with a small shaft kicking out of gear when I slow down. It's on 22 ft Cougar MTR with twin 280's, one has a fat shaft (original leg) the other has a small shaft (must've been replaced). When I let off the throttle quickly the small shaft will kick out of gear. I've chewed up one set of gears and I'm still having trouble with it. Any ideas or recommendations on how to fix this would be much appreciated.

[johnmiffco]

prop shaft diameter has nothing to do with the internals
as uses same carrier/bearing size,,,shaft just tapers down more for 1" splines vrsing 1 1/4"
fatter shaft less breaking off chances
its how was "assembled" for proper spacing/clearances/resistance/ect
also making sure shift cable is full engaging the gearsets so don't round out gears through time