40A fails during new engine water test

Today was the big day to do the first water test on the rebuilt GT40 in my 96 Sport. Engine ran like a champ...so smooth until the 40A tranny decided it was not happy.

The original 40A 1.23 transmission was replaced in 2010 with a 40-2A 1.258 (other thread on the whole naming convention just last week). The transmission was running fine until the engine started having issues in 2014 and was parked. Boat has not been in water since then. Since the tranny was replaced in 2010 (date stamp on the new tranny is 2010 too) and was only run about 400-500 hours before boat was parked, we were not expecting any tranny issues.

Transmission got drained and filled with new fluid yesterday.

At idle the 40A was quiet and cool. Went into gear easily and boat started moving well. As the RPMs increased there was a slight noise that grew then at 3000 RPM the tranny locked up and killed the engine. Checked fluid....no milkshake and still full.

We restarted engine (cranked fine) and got into gear. Took it easy for a few mins at about 2000-2500 rpm. Slowly opened up and again near 3000 rpm same thing happened. At this point tranny was quite warm to touch and even at idle there was a slight rythmic squeek sound. We took it easy back to the dock.

We pulled the unit, damper looks good...the issue is definitely internal in the transmission. After the transmission was out, you could turn the tranny by hand and it would make a knocking sound.

My buddy who lead the engine project at his shop doesn't do much with transmissions. He sends them off. We called his transmission shop that is the regional go-to shop. The owner said that the symptoms we described weren't unheard of but were slight odd. His best guess without opening it up was that fluid is leaking through a seal (or something to that affect) and throwing the transmission into reverse causing the engine shut down.

He said same thing everyone here does...if we replace it, go with a new 80A. But he said it work him opening up, it could be simple and not require an evasive rebuild. Of course he won't know before he sees it. He is about 3 hours away so we are going to ship it over to him on Monday. Shipping is about $80 and he will diagnose it for $100. If unit is beyond reasonable rebuild and we decide to go new, we can pay the $100 diag or just let him keep the unit for parts. It seems he is leaning towards it being repairable. With all the other projects on this boat and just paying for the engine rebuild, a new 80A at the current USD to CAD exchange rate is pretty unaffordable.

Any ideas on what the problem may be and the odds of fixing it? Oh great guru of transmissions FFImarine you got any thoughts?

Here is a video of the sound after removal:
Click here if embedded video doesn't work: 40A Knocking when turned by hand

FFImarine wrote: Tagging FFImarine

Thoughts anyone? I'd love some speculation on this transmission.

Sounds like it’s locked into a gear and you have bad bearings in the reduction housing I apologize for the late response but if the forward clutch drum isn’t cracked it will be able to be rebuilt. Also sounds like it may have overheated at one point to cause the issue. If you have any more questions please feel free to call us anytime 330-273-8291 our rebuild cost $1,400 plus shipping both ways and comes with a 1 year unlimited hour warranty

Hahaha I thought the name looked familiar