1991 75hp L.U swap to 1994 115 work?

[ultra353]

Hi, does anyone know if a 1991 Mercury 75 20” lower unit will fit a 1994 115 with a 25” w/removable spacer .
Need a 20” for my boat as my 75 oil pump went out and rod went through block,
This 115 is available but is the 25”xl motor and I was wondering if I could just swap the L.U . Thanks

 

[QBhoy]

I honestly can't be confident enough to say with certainty, But I am almost sure that there is certainly a difference between the gear ratio that each have. The 75 will have a lower ratio than the 115. Be something like a 2.3-1and the 115 about 2-1 or something close. That should be considered. Someone else better than I can confirm if it will actually fit. As far as I know, generally speaking and outwith the Bigfoot models of the era, the 75-125 range of mercs around then might just be from the same stable..or at least certainly use the same prop fitment for sure.
Hope that helps

 

[ultra353]

Thanks for your reply. I’m not sure either.
Seems like the driveshaft #’s are the same so I figured I’d ask on here to see if it was possible

 

[QBhoy]

Thanks for your reply. I’m not sure either.
Seems like the driveshaft #’s are the same so I figured I’d ask on here to see if it was possible

Ok. Will likely just be a case of one of the guys on here, saying if the bolt pattern is the same or not. For the most part and generally speaking, I’d think the gearcase size of the common type 75-115/125 around then, is of the same size. Usually at least. Someone more confident than I about it, will be along soon, I’m sure.

 

[Faztbullet]

Gear ratio is different, as long as you dont pull skiers or tubes you can play with prop pitches to regain lost RPM

 

[ultra353]

I appreciate the clarification , thanks