Honda BF90A - broken drive shaft

Hi all, long time lurker first time poster.

I have a 1999 Honda BF90A which appears to have been shortened from 25" to 20". The drive shaft failed when shifting into reverse this week and looks like the shaft has been cut and welded in the past. It is a Honda gearcase.

I'm in Melbourne, Australia and struggling to find a replacement shaft or lower unit. Can anyone confirm the part number for the required drive shaft and if there is any compatibility with later models or parts? I've heard I could potentially fit a newer lower unit however can't find specific info.

Many thanks in advance!

Sorry you were the victim of a hack. Expecting a weld to hold there is quite a stretch of the imagination....

Actually Mercury built that gear case for Honda. Honda didn't start making their own cases until recently. As far as interchangeability, there's a 97-98 Honda case (pre 99) with virtually no interchangeability. The 99 and newer, up until at least 2007 or so, will all work. 75's and 90's are the same. I DON'T know if the Merc drive shafts will work, though I know stuff like water pumps do. Probably worth checking into further if you have access to one of those, though you would likely have to lay new/old side by side to be sure.

If you'd like to confirm which case you have (old vs. new), post a pic. I can tell them apart in a heartbeat.

Best of luck! -Al

Thanks Alan! I can't seem to add photos, however it's definitely the post 1999 Honda box - plastic impeller housing etc. Sounds like this should be interchangeable with most newer boxes then. I've tried to identify the correct drive shaft part number online and a few different part numbers come up for these boxes across the years: 41112-ZW1-B01, 41112-ZW1-B02 and 41112-ZW1-B03 - do you have any idea if these are interchangeable?

When I look up those numbers, B01 is discontinued, and B02 has been superseded by B03. So it appears you are looking at 3 different revisions of the same part.

This is the one you are after, listed in one of the best on line manuals I've run across.
https://www.boats.net/product/honda/41112-ZW1-B03


And you're right. The plastic pump body will positively ID the newer lower unit. Early ones (97-98) are metal. -Al

Brilliant, thanks so much Alan!

Hi Alan, I've located a BF90D gearbox locally in good condition. Do you know if these will bolt up directly? From what I can tell, the drive shaft and gearing is the same. I will go and inspect it when I get a chance, but thought I'd check if you have any experience here.

pluralses said:

Hi Alan, I've located a BF90D gearbox locally in good condition. Do you know if these will bolt up directly? From what I can tell, the drive shaft and gearing is the same. I will go and inspect it when I get a chance, but thought I'd check if you have any experience here.

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If it has the plastic water pump you should be good to go. Bolting a used lower on is WAY easier that replacing that shaft. My biggest concern would be the condition of all the seals. Maybe it should go without saying, but make sure you check the fluid carefully!

It definitely has the plastic water pump - the housing looks like a slightly different exterior design on the newer model however where it interfaces with the engine casing it looks like the same profile. Fingers crossed!