BF90AX XRTA Lower unit compatibility

My frame is BBBU-4000400's and I'm looking at a lower unit from BBBU-1000000's
reading the year charts makes mine a 99 BF90AX and the donor a 97 BF90AT
I can't find if they would match up.
The 97 is a smaller capacity and it's visibly a little different too.
but I only have pictures to go from

Any idea?


Why the swap?
when I shift it doesn't grab hold and chatters at low speed.
I've adjusted the cable which was part of the cause but damage is done.
I just want to get back on the water.
I prefer to learn to rebuild my gear case but summer is fast passing me.
i changed the gear oil month back and just dropped the lower unit, it shifted fine with plier on the shift rod. Then reinserted it. As I was doing so gear oil leaked out the inflow screens.
So I've definitely some work in front of me to replace gaskets, seals, and water pump and potentially dog gear.

Should i I just take th lower unit to the nearest honda marine tech?
My original is on left, with the toolbox.

They are not compatible. The AT is a Mercury gearcase.

The shifting problem, could be anywhere from your clutchdog and/or gears, to the shift linkage up on the engine (they wear out especially if you are shifting a lot, like they do on a workboat). If is also possible that you have an older Honda shifter, that was made by Mercury that never really works well.

I would take it to a tech and let him look over the whole setup. He may be able to zero right in on the problem.


Mike