Would the '74 115hp Evinrude gear case work on a '75 135hp Johnson? From what I can see it should work but would appreciate input from you pro's. Thanks
You've got some old part number questions. The old OMC data base sheds a clue. It does not show any supercession between the years of these units.
But there is a hint that this will work on the factory part description of the 75 135 lower unit: 387580 gearcase 73-76. They should interchange.
Don't give up on swapping the gearcases. The 115 case ratio is a slightly lower ratio. On the 135, you'd have to run that 115 gearcase with a higher pitch prop than the one you ran on the normal 135 case. Other than that, I doubt you'd notice the difference.