TOPIC: Lower unit interchanges?

Hi all!
I'm wondering what Johnson models and over which years I can the lower units interchange? I have a 66 40hp with a bad one with damaged case.

Depends on the model. There were two distinct 40s available in that era. One with electric shift, one with mechanical shift. They are not interchangeable. There are also long and short shaft versions, but those can be modified with the appropriate parts...

The model is a RDSL 28B

And is mechanical shift, as out has a shifting lever on the side of the engine.

I believe any of the mechanical shift lower units from the '60s era Johnrude 40s will work for you. The Gale 40hp lower units will NOT, as they use the single-wall mid-section which has a different bolt-up pattern. Some of the very late Johnrude 40s used a different waterpump arrangement, as noted by one of the tubes leading INTO the lower unit housing, rather than upwards into the motor.

I may have a lower unit for you if you're interested. I picked up a pile of Johnrude Big Twins last weekend and one of them was a mid-60s Johnson 40 (same unit). I haven't had a chance to look it over closely yet, but it does appear to need seals. I will delve into it soon to see if it's any good...

- Scott

Thanks Scott, let me know if you have one. Meanwhile I'm going to pull this one down and see whats going on with it. Bought it and the stand for $100 over the weekend mainly as a spare...