Why is this driveshaft different? 81 and 82 Johnson 25 Lower Unit

[CullenTN]

I fried the gears in the lower unit on my 81 Johnson 25 so I picked up a good used lower unit from what they said was an 82 Johnson 25 off ebay.

I got it in today and the driveshaft on the 82 is a smaller diameter and instead of splines where it goes up into the motor like on my 81 it has this kinda square looking deal.

I looked up both of these lower units on the parts catalog and cross referenced and all the part numbers matched...so what could be going on here?

My guess is:

1) The lower unit I got isn't really from an 82 (but pretty much all the other parts match up. Even the pinion gear had the same number of teeth. I tried swapping the driveshaft from my old one but it wouldnt fit due to the smaller diameter on the 82 unit.

2) My lower unit may have been replaced and maybe they changed the driveshaft and also changed whatever it is that goes up into the engine?

Can I swap out whatever the driveshaft connects to up in the engine to take the driveshaft from the 82 unit? Or should I just buy a new pinion gear and swap the gear set from the new one into my old unit?

What should I do?

 

[CullenTN]

Re: Why is this driveshaft different? 81 and 82 Johnson 25 Lower Unit

I went to the local boat shop they wanted over $1000 for new gears so I found a lower unit in good condition with a prop on ebay for $250 and got it. It was advertised as a lower unit from an 82 and after cross referencing the part numbers they all matched. Well when I got it not everything matched. The driveshaft was different and it also had a shear pin on the prop shaft. I'm pretty sure the lower unit was a 70s model. The gears were basically the same otherwise so I swapped them into my lower unit along with the prop shaft and bought a new pinion gear since it was different and mine was trashed and everything seems to be working real good. I kind of like the idea of having a shear pin now too because I run in small rivers a lot that have a lot of trees and my props always get all dinged up. Maybe this will help.

 

[1946Zephyr]

Re: Why is this driveshaft different? 81 and 82 Johnson 25 Lower Unit

I have seen commercial grade 25's with different lower units than the typical models. I had a customer bring one in and I bought a used one for it. When I got the used one home, it wouldn't even come close to matching up. The one I bought had the typical drive shaft and the motor my customer brought me had a multiple spline on the top. I ended up cutting exactly 6 inches from both drive shafts and coupling the original top piece to the new lower unit, after the motor sat in my posession for a few years and the owner didn't want it anymore. LOL I got it running and it ran fine, so I sold it for 600 bucks