1981 MC1 endplay in prop shaft? replace lower unit SEI / Jasper / Thoughts??

merc120_81

Petty Officer 3rd Class
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Jun 20, 2011
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92
hello all,
I have a 1981 120 with MC1. My lower I think is on its last legs, shifting no matter how much I adjust into reverse is getting bad, and it seems to me there is quite a bit of movement (end play? in and out on the prop shaft)
From what I have read, rebuilding these lower units, is not for the faint harted or fully equipped specialty tool folks..

so.. is it showing signs of dieing?
if so..
replace with what?
what fits/what doesn't if I am keeping the upper?

thanks all.
 

Bondo

Moderator
Staff member
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Apr 17, 2002
Messages
71,308
in and out on the prop shaft)

Ayuh,..... That in/ out play is normal,......

I'd sooner think you need to replace the lower shift cable,......
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Check all the shift system for slackness and 'slop', that's likely where the problem is. Over time places like the upper and intermediate shift shafts increase their tolerance. Sometime all it requires is the 'shoe' on the end of the upper shift shaft to be squeezed a bit to tighten it up, or the grub screw in the end of the shift slider to be tightened back up to it is specified 'end float'.. Simple things like that can be the difference between working and not working.

Chris..
 

kenny nunez

Captain
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Jun 20, 2017
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Disconnect the lower cable, push it in while someone turns the propeller to lock it. While they are holding the propeller try pulling the cable to see how much slop is present. As Chris said start looking at the connection where the shift shoe contacts the bronze lever. If the slop is in the lower gear housing then the shift spool has worn over the years. This can be repaired but the lower gear housing has to be completely disassembled. Hopefully that is not the problem and might be the shift slider or cable.
 

merc120_81

Petty Officer 3rd Class
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Jun 20, 2011
Messages
92
thanks all, going to try a bit of tweaking tonight..
I fear that with this being 39 years old.. the lower spool migh just be ready to retire..

@ Achris.. what is the grub screw? "the grub screw in the end of the shift slider to be tightened back up to it is specified 'end float'.." And what is the specified endfloat?? I haven't seen that documented. I will have to recheck the merc manuels
 

merc120_81

Petty Officer 3rd Class
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Jun 20, 2011
Messages
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...lower shift cable was done 2 years ago.. low hours ,since then, trailered boat, garage kept, fresh water.. ... hope its not the cable..
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
thanks all, going to try a bit of tweaking tonight..
I fear that with this being 39 years old.. the lower spool migh just be ready to retire..

@ Achris.. what is the grub screw? "the grub screw in the end of the shift slider to be tightened back up to it is specified 'end float'.." And what is the specified endfloat?? I haven't seen that documented. I will have to recheck the merc manuels

In 30 years of working on these drives, I think I have seen 1 case of a worn shift spool. Every case of poor shift adjustment has been a case of something easily fixed, and relatively cheaply, with few parts.

This from manual #6... They call it a set screw. It's without a 'head', so I call it a grub screw..

setscrew.JPG
 

merc120_81

Petty Officer 3rd Class
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Jun 20, 2011
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92
Achris.. spot on as always. Rather than pull the outdrive off, I adjusted thre lower shift cable agaun.. it was off by probably 1/4" ..maybe not that bad.. but. she is shifting nice in the driveway.. hopefully the sea trial thursday or friday gies as well

you guys are the best.. thanks again.. will update when i get her on thr lake again.
 

merc120_81

Petty Officer 3rd Class
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Jun 20, 2011
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All shakedown went great. thanks again.. for putting me back on course.
 
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