1956?ish Evinrude Fleetwin slipping out of gear???

So I recently bought a boat that has a fleetwin 7.5 on it. I was out running it today and everything was going fine until it seemed to start slipping out of gear and winding up really high but not going anywhere. . . It only happened one time, limped back to the dock and went out closer and ran it hard to see if I could make it happen again to diagnose but it wouldn't. It was at full throttle when it happened and would start pushing again when backed off. Did this about 3 times but I backed off and got close to the truck in case it totally went out.

Is there some sort of gear or something in the lower unit that is causing this? It might also be that I'm an idiot and didn't have it fully engaged in FORWARD. . . but it seems that I have seen outboards do this before (mostly from the props with rubber inside that slip when you hit something (shear pin type idea) that the rubber goes bad on).

Any help would be much appreciated! Kelpy

Re: 1956?ish Evinrude Fleetwin slipping out of gear???

Well, it COULD have been cavitating. Any weeds or stuff around that could have got tangled up on the lower unit?

Also, it COULD have a broken spring in the shock absorber. That also sometimes makes them lock up.

The 7.5 does not have a rubber hub, so you know it isn't that.

Re: 1956?ish Evinrude Fleetwin slipping out of gear???

What parts/covers would i have to take off to get to the pictured parts to check it out? Just making sure that I'm not digging into the wrong spot and taking apart something I can't figure out how it goes back together. . .

Thanks for the info, Kelpy