Shift rod Seal Repair for Mercury 3.9HP Vintage Outboard Lower Unit Gearcase

In this video, we perform a shift rod seal replacement procedure on a vintage 1968 Mercury outboard lower unit gearcase. Especially on older outboards like this one, the seals break down and eventually fail as the rubber dries out and lose resiliency. Occasionally, they need to be replaced. This procedure will be similar for other outboard years and other makes and models.
Tools needed for this seal repair are:
6mm box wrench
Pliers
screw driver
Blow torch
3M 847 marine sealant

[@CapMC47]

Dropped my lower today to replace the impeller. Found a fair bit of milky oil. But the oil in the lower looks good. Will be changing this seal and flushing out the lower unit oil. I think the water got in from the tube that extends out of the impeller housing. It was in pretty bad shape. Replacing that aswell. Thanks for the video. What a relief

[@mgarner79]

This was exactly what I needed to get a friend's Mercury 4.5 HP sealed and back on the water. Thanks!

[@darwinottolini]

Unfortunately you left out that little tidbit of how to reinstall the shaft. I have been trying for hours to get mine back in but cannot

[@peterseyler7295]

i am currently experiencing this same issue and cannot put my lower unit back on due to it. i have tried almost everything, and am going to head to the shop next week. please let me know if you found out how to reinstall it!

[@74nova36]

So if it leaks will it just enter the boot, and mix with water that cools the motor, also flowing thru the water jacket; all before exiting out the pisser?

[@ricksnowden8408]

Always lube seal to shaft

[@swankydave]

I have had a heck of a time getting the casing out, too. I've pretty much scraped all the rubber out, but the casing is pretty tight in there. I know I should try heating it up, which I will do. BUT... if I don't have any luck getting it out, am I able to purchase the entire seal assembly from somewhere? Might you know what it would cost me? P.S. Excellent videos. I got my hands on the same outboard motor and if it wasn't for your videos, I would be lost trying to fix mine. I've had the same issues as you've had and the videos are SO helpful! Thank you so much for the help!!

[@74nova36]

Any idea what the thread pitch/pattern is on these drain ports? Going to buy an adapter

[@dennisfalan1623]

What is the part number for the shift shaft seal on a 1968 Mercury 39? Thanks for the video is helping me a lot restoring this old outboard!

[@wyattsanders9720]

After I took the shift shaft out it would not go back in and the splines are fine I can’t figure it out have any idea??

[@sudsmonie]

after putting the lower back in,i can't get it in gear,tried about 6 times now! need help

[@dennisfalan1623]

Is water supposed to leak from the weep hole above the prop shaft everytime after running for couple mins?

[@highlandoutboards]

Yes, that's normal.

[@thomasflynn642]

can't get seal casing out! tried everything,any ideas? when are you going to respond????

[@highlandoutboards]

Try using a hand held butane torch like you can get at home depot, and apply some gentle heating to the seal bushing. Not too much -- don't want to get too hot or cause a fire. This should loosen the thing for ya.:) I suppose the market for free advice demands faster response times than it used to!

[@thomasflynn642]

can't get seal casing out! tried everything,any ideas?

[@highlandoutboards]

Sometimes I use heat from a hand-held propane torch to loosen up stubborn seals. Don't heat too much or the gearcase oil will burn.

[@jeffdebord4506]

hey james, any chance ud call me if i gave u my number ? i have a question about a 68 6 hp mercury and im in a bad spot.