Wrong Diameter Drive Shaft? '01 50hp & '93 40hp

[Chicklin]

Hello,

I have a 2001 Johnson 50hp with a shot lower unit. My mechanic recommended I buy a used lower unit rather than rebuild my old one (he said it would be cheaper). I found a lower unit from a 1993 Johnson 40hp (it was cheaper than the price he quoted to rebuild my old lower unit). I thought those lower units were interchangeable. Although everything lines up (bolts, shift rod, drive shaft length), the diameter of the power head end of the 93 40hp lower unit is tapered down to 1/2 inch diameter. I believe my old lower unit's drive shaft was 3/4 inch diameter, but I don't have it with me (it is still at the mechanic's shop). So the new lower unit's drive shaft will just spin inside my power head. Now what should I do?

Can I swap out the 1993 40hp lower unit's drive shaft for my 2001 50hp lower unit's drive shaft? What would be involved in that swap - would it just be a simple drive shaft swap or would I have to swap out gears and linkage...

Or do I have no other option then to start over, sell my '93 lower unit and find another lower unit?

If I have to start over, how do I keep from having the same problem in the future? Everything I have read here makes me think the '93 40hp should be identical to the '01 50hp??

Thanks for your help!

 

[clanton]

Re: Wrong Diameter Drive Shaft? '01 50hp & '93 40hp

You have to measure your drive shaft, and find a match. The shafts are all not the same.

 

[Chicklin]

Re: Wrong Diameter Drive Shaft? '01 50hp & '93 40hp

Does that mean the drive shaft's can't be swapped? I would be surprised if they can't be swapped since both drive shafts are 3/4" when they enter the lower unit. But obviously that would not be the first time I would be surprised in this project.
In checking shop2.evinrude.com - The two different years and hp motors have different drive shaft part numbers (wish I would have checked that before), but they have the same forward gear, reverse gear, clutch dog...

 

[clanton]

Re: Wrong Diameter Drive Shaft? '01 50hp & '93 40hp

The 40HPs had a lot of drive shaft breakage, size was increased to cure the problem. Water pump impeller was changed also. IF the orignal shaft and gearcase is good, I would rebuild the gear case.

 

[Chicklin]

Re: Wrong Diameter Drive Shaft? '01 50hp & '93 40hp

Thanks for the advice. If I had to do it all over again, I would probably pay the extra to just have my old lower unit rebuilt.

 

[Chicklin]

Re: Wrong Diameter Drive Shaft? '01 50hp & '93 40hp

So I took both lower units to a mechanic that simply swapped the two shafts. We have been working the new lower unit for a couple weeks now without a problem. I even toed a guy across the lake because his lower unit went out. Thanks for your help!