Mercury Lower Unit HELP!

I bought a new to me lower unit (lu) and tried to install it yesterday. Got it in multiple times but gears incorrect. Several times forward and reverse seemed to be right but prop would click when in neutral both counter clockwise (cc) and clockwise (cw). Perhaps shifting cable needed adjustment? Perhaps I’m a moron (save judgement, it gets better). Anyways, played with it longer than I’ll admit and went home feeling like a beat horse. Started looking around on YouTube more about situation and ciphering which guys had a clue and who were down at my level so as not to listen too much and I had an epiphany; the lu that was on my boat, just had a male, splined shifting shaft and the one o bought has a male, splined shaft with what looks like a can that a detent pin would ride on as you select gear.

the pic above is the new to me lu.


this was lu that blew pinion gear.
We checked motor serial numbers and they should be the same lu. They also both came from 1986 Mercury 75 hp motors, 4 cylinder, 2 strokes. Housings identical. I may have lost collar from my lu but seriously doubt it. I don’t recall tipping it over or it falling over. I also know when I removed prop shaft from mine to get to pinion gear, the detent pin was loose behind forward gear, not up above.
will this lu work? Do I remove collar from it and continue? Any and all advice welcome. Thanks in advance and off for a beer awaiting words of wisdom!

That unit on the shift rod is for the REVERSE LOCK cam.------------The shift pin that goes into the propshaft is loose on all of them.--------There is a strong spring inside the propshaft that confuses some folks on how these work.------Put the lower unit in neutral by turning shift rod CCW and put control in neutral.----Then assemble.

Ok, I’ll do that (again�&#56618. Several times when I got there yesterday everything seemed right except in neutral gear, prop would click when spun either direction. It wasn’t in gear for sure but there was clicking. If I get there again should I adjust shifting cable or is something still wrong?

Also, there’s nothing in bottom of motor to run on that cam. I think it’s operation is beyond my pea brain!

There has to be a shift pin in the end of the propshaft.------Time to take it apart.---Find it on the shop floor.----Parts cleaning tanlk or order a new one.

There is a pin at end of prop shaft. The reverse cam? lock that goes over the male splined shift shaft that connects to shift rod from motor, has no pin or anything that I can see that runs on the angled part of reverse cam lock. My old lu didn’t have a reverse cam lock on it. I have very little to set it properly. All I can find is that in forward, the 90 degree angle side should about be lined up with speedometer nut, toward front of motor. Once that is set (may be off a tooth either way) I need to shift lu to reverse and boat controls to reverse OR set them both to neutral and install. I’ve done this an embarrassing amount of times but cannot seem to get all 3 gears to work properly. I keep playing with reverse cam lock, moving it a tooth at a time. Hopefully it hits right soon. My current mood wants to list and sell motor! Completing job will erase all that I hope. Thanks again!