moth ago boat ran fine, nothing changed, 3 weeks ago took the boat out, no wake zone all was good, pushed down on throttle, motor rpm's went up, and boat went no faster, sounded like a clutch slipping. 1st thought was spun hub in prop, ss prop with a pressed in hub, replaced the prop, and verified with erie prop (nothing wrong with prop, needed a spare anyways), no difference. pulled outdrive, no shavings inside, no burnt rubber smell. put a old spline shaft into the coupler, with a steel rod welded to the end with a socket welded to that. put a breaker bar on harmonic balancer, wedged up against a stringer, then put a breaker bar on the back with a long pipe on the breaker bar. stood on the pipe, couldn't turn the coupler. Next was told that it had to be the clutch cone in the upper half of the outdrive. 30yr merc tech said that it was the only thing it could be. he pulled it apart showed me the parts he removed, said that this was definitely the problem. checked alignment, and put the outdrive back on. Put it in the water, SAME THINK. Not fixed. ANY IDEAS, OR COME AND FIX IT.
You really cant check a coupler like that because your not 300Hp strong.
If the gear and the bronze cone are good, the drive will not slip. You say you changed the prop but did you actually check the prop. Remove the prop and punch 2 index marks and retest.
If not the prop ,the best guess is the coupler .If it is it will burn itself out with use.
