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gear case compatibilty

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shawnbradley

New member
Hi all,
I'm kinda new here and new to boating. I am having issues with forward and reverse gears. I'm pretty sure it's the dog clutch. I removed the prop and bearing carrier retainer nut but I don't have a puller to remove bearing carrier. Also, the gear oil looked terrible. Water getting in. BTW, I have a 1979 80hp 4 cylinder merc. While shopping for a puller, I decided to check Craigslist for parts and I found a lower unit from a 1974 85hp merc and I was wondering if it would fit my engine. The '74 has a 20" shaft, good seals, shifts great. Not sure what the shaft length is on my 80 but wondering if I could swap shafts as well?
Anyone know if this is doable?
Thanks for looking, hope to hear some ideas.
 
One of the things Merc messed with in those days is the splines on the shifter: most were the usual 6 splines, but some used a square shaft design.

Most were long shafts--shorties are rare.

You can get the guts out of the case by using the prop as a puller. Stick plywood pieces between the prop and housing then, messing with washers (and ingenuity) tighten the prop nut and pull her out. If it absolutely won't move you'll start tearing the rubber hub apart, so stop and scrap the thing.

Jeff
 
From what I can find they only came in 20" shafts. Your LU should have a stainless steel driveshaft around the water pump area which makes it desirable the '74 probably has carbon steel which is less desirable; if you want to get the bearing carrier out I would say to soak the exhaust area with a penetrating solution for a few weeks, it is possibly "welded by corrosion" in place I had that problem and see the results.... trashed-LU.jpg
 
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One of the things Merc messed with in those days is the splines on the shifter: most were the usual 6 splines, but some used a square shaft design.​
Click to expand...
The square shaft shift rod was never used on the I-4 engines....
 
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