Shift Shaft problems

[mdog2020]

I recently replaced the impeller in the lower unit of my 1991 Yamaha L250TXRP. The first time I put it back together I missed the alignment of the shift shaft from the lower to the upper unit. The engine would crank and rev up but the prop wouldn't spin. I took the lower unit down and realigned the shift shaft and all was working fine. I've had the boat in the water 3 times since the work and yesterday while boating 20 mph I hit a wake and it felt and sounded like I lost propulsion and I had. I could tell when I throttled up of down that the engine was not engaging into gear. It did not make the noise the gears make when engaging and the tension at the throttle controls was different. I have not had a chance to work on the boat yet but I'm pretty certain it's the same symptom of the shift shaft connection between the upper and lower unit. I didn't put a clip or pin of any kind on the shift shaft at the joint of the upper and lower unit. Should there be one? Did I not push the two together all the way? Is it possible to have this joint disengage on it's own? Any tricks on this from the pros?

Thanks so much.

[jb123]

look above cav plate to see if the shaft is rusted if not stainless
remove cable from motor linkage and shift by hand to see
if it worked for a few weeks then now not, most likely another issue

[mdog2020]

Rodbolt any thoughts?

[rodbolt17]

I am with jb123.
carefully inspect the shaft.
the pre 1995 yamaha shafts were prone to rusting in two.
shaft cannot dissenguage once installed.
have someone shift fwd,n,rev while you are rotating the prop.
make sure the shaft rotates.