73 Merc 850 LU shifting

[erniex]

Pulled LU to replace water pump, check seals etc. I was checking the shifting from F - N - R by operating the lower shift shaft with a socket wrench. The unit clicks and locks solidly into forward and reverse, however when I shift it out of forward into neutral I am still getting some gear contact in what should be neutral (midway between F & R). Only when I start shifting to reverse do I get true neutral (no gear contact)right before it shifts but it doesn't hold. If I release the shaft at this point before it snaps into reverse, it doesn't stay and the spring action pushes it back to the midway neutral position and I have gear contact. I don't think this is correct and don't want to reinstall the LU until I'm sure it's right. Any thoughts or comments will be greatly appreciated. Thanks in advance.

 

[Gus Mortimer]

Re: 73 Merc 850 LU shifting

I have never actually done this on my lower but I think I remember the manual saying that it is spring loaded toward forward in case something happens you can still get to the dock.

 

[Chris1956]

Re: 73 Merc 850 LU shifting

Ernie, That LU should "snap" and stay in neutral. It has a shift cam with squared off "steps" for each gear. There is a spring inside the prop shaft which pushes the shift dog into the forward gear. The neutral cam compresses the spring some, and this should be true neutral. The reverse cam compresses the spring more and forces the shift dog into the reverse gear. In forward, the prop shaft will turn clockwise, with a racheting sound. In reverse, the prop shaft will not turn either way. If you do not find neutral when the shift shaft is solidly on the neutral cam, I would think you have a problem.

 

[erniex]

Re: 73 Merc 850 LU shifting

Thanks for the reply. So you're saying when the the unit is shifted into neutral and rotational pressure is released from the lower shift shaft, the unit should be in true neutral and stay there without assistance. I assume also that I should not have to rely on the tension/pressure from the control cable (when connected) to keep it in neutral.Everything else is as you described relative to prop shaft rotation. Any clue to the problem? Could the shift cam be broken or out of place or is it more likely the shift dog? Probably need to open it up to find out.

 

[Chris1956]

Re: 73 Merc 850 LU shifting

Ernie, It should stay in neutral without any pressure, at least that's how my 1977 IL6 outboard works. The '88 Mercruiser I have does not stay in neutral, but automatically shifts to forward unless you hold CCW tension on the prop, so I guess Mercury has at least two designs!