Are Johnson 1971 and 1972 lower units interchangeable on a 100hp?

[WI-Fisherman]

I have a Johnson 100ESL71C which is leaking oil in the water jacket, taking water into the oil, and failing to shift out of forward. I found a lower unit for a good price, but it was taken from a 1972 motor, and the part number for the casing is different. Are these lower units interchangeable?

 

[jbuote]

No Expert, but I think they might be.. (Don't quote me on that though...)

​I have to ask....
Why are you looking for a new lower?
​Could be seals in the current lower letting water in. Pressure test would tell that story (Fixable).

​As for shifting, if it's not shifting out of forward, I believe that's because it's Hydro-Electric. (71-72 were hydro I think even for the 100's)..
​IF no power goes to the shift solenoids, it defaults to FWD..
​Power to green is Neutral, and power to both green and blue is reverse.. (For Hydro-Electric only)

​Could be shift switch is bad, solenoids have issues, etc..

​If it were mine, I'd probably do some more troubleshooting to determine what is actually wrong before I shopped for a whole new lower for it..

Mind you, I am really new to outboards, so I could be wrong with some of this.
​
For what it's worth..

 

[thelegion]

Hello there
I have the same motor and mine has had the lower end replaced with a 115 lower, I can double check when I get in but pretty sure.

ok, well I'm home now and my lower end was replaced by a 125 bottom end, it still has the paint markings on it from where ever it was replaced from. There is a local guy by the name of "stomping tom" who has about 200 + outboards in his yard, he might be abel to answer your question in a heart beat. It would take a call to Canada but the long distance charges would be worth it just to chat with him. PM me if your interested, the motor I have is super nice\clean under the hood and runs like a top, oh and if your shift switch ever goes in the control box there is an Aussie on youtube who replaces it with a battery selector switch.

 

[WI-Fisherman]

Thanks for the responses. I apologize for not getting back sooner, but I had expected to see an email when there was activity on this. I'm new to the forum. I got a good deal on that lower unit, and it seems to be working well on the hose at least. Now I plan to take the old one apart and fix whatever may need fixing. It may have been a more expensive route to go than necessary, but at least I'll have spare parts now. Thanks again for your responses.

 

[TN-25]

I would also expect the 71 & 72 lower units to interchange. It was on the 1973 models that they changed to the Powershift II & also the added the provision for motor mounted Teleflex cable (rather than strictly transom mounted).

 

[jimmbo]

No reasons why it won't fit