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Bravo 3X upper gear set failure

T

tb0ne

New member
My intention to start this thread is for any and all experience with the failure of the upper gear set of a Bravo 3X outdrive, powered by a 496MAG HO for a 2005 Formula 260SS with under 500 hours of operating time. A fresh water boat, maintained very well with annual preventative maintenance and fluid changes to Mercuiser specs. Family boating usage with only occasional high RPM usage. I DID have the clutch cone replaced with OEM part the winter previous to said failure. I'll get OM Serial numbers for a future thread.

I would like to know if it's common. Which from searching many boat and Mercruiser forums, it does not seem to be common.

Also, I would like to know the 'occurance' that may have caused your particular failure, if not determined to be from 'wear'.

Any opinions (oh boy!) on the clutch cone replacement and it's potential effect on upper gear set failure.

I'll leave it at that for now and hopefully information can flow if this thread takes off.

Cheers
 
Ayuh,.... Welcome Aboard,... The most common cause of all Upper failures is low oil,....

How much oil was drained,..??

Any water in it,..??
 
As Bondo stated low oil can be a cause....


You had another post about this issue and never responded after the last post.

What exactly is the failure? Are the gears coming apart? Bearings seizing? Cone clutch prematuring wearing out?



Maybe some more detailed info might be helpful....
 
Bondo, that is a very probable source of failure (low fluid/water) I agree, but not in this case however. The fluid capacity was adequate and no water evidence. That was one of my first inquiries on initial investigation as to the cause.


Kghost, great catch on the post, my mistake, I thought that last post was on another forum site. Rookie move. However, if I'm not mistaken that post you mentioned was specific to the cone clutch, was it not? As mentioned, my intent is to proceed specifically toward anyone's experiences with the failure of the upper gear set, as in this case. (You're right though I should have probably continued with that previous thread.)


regardless, the two different Mercruiser technicians both confirmed, specifically, a failure of upper gear set. I quote: "we believe the upper drive shaft bearing set was starting to seize causing the noise described previous to failure. Eventually, locked up causing the drive shaft housing to break and in-turn take out the gear set, clutch and bearings."


Both Mercruiser technicians reacted the same way upon first seeing it. "Wow, what did you hit"?!


In retrospect of their reaction, I could think of only two probable occurrences leading up to the failure. One being a 55-mile trek across Lake Erie, trimmed up and running 3000'ish rpm to ride wave crests ('wave-hopping' is a term brought to my attention) where it's possible the prop exited and re-entered the water multiple times. As anyone would know the significant density differences from water-air-water are extreme enough to potentially provide a re-occurring strain/stress on the gear set/drive, inevitably causing failure.


The second occurrence was a soft grounding on a shallow sand bar. Boat on plane, low speed, and a grounding that brought the boat almost to a stop, and stalled the engine. Post event inspection on scene revealed no visible damage and the motor started and ran fine immediately afterward.


Those two events occurred within one week previous to said failure. No bent props, no vibration. The grinding and 'grrrr'ing' noise(s) started approx 2-4 hours operating time prior to failure.


Recap--I'd like anybody to share probable causes of their experience if they were so unfortunate......:-/
(or was it just it's 'time' kinda like us?!)


Cheers
 
Personally I would not say wave jumping would be an issue........no real load on the drive other than maybe an over rev.

I have a friend who waved jumped for years........never blew the drive!


Hitting the sand bar and causing an abrupt stop sounds more like the cause....

think about how the engine was stalled? The prop stopped spinning in turn causing the gear set to stop spinning in turn stopping a 400 hp motor to stop turning.......


I would not say the bearings took a dump, I would suspect a gear tooth took a dump first.


The upper gear set is closest to the motor thus has the most torque applied to it.

Example, before the bravo outdrive was introduced around 1988/1989 boats equipped with 454's used the Alpha 1 gen 1 outdrive. Problem was the torque from the 454 blew out the upper gear case of the alpha's, chronic problem.

Now I am no expert on the bravo upper gear case and have not worked on enough to see any catastrophic failures.


In your last post I referred to the incoming water connection at the transom. This is a area of concern!!!

The pinch fitting is aluminum and oxidize/corrodes causing the hose to be pinched thus restricting flow.

If this is happening and you have thru outdrive exhaust then the drive could be getting warmer than it should due to restricted incoming water. It may not affect the motor temp but the exhaust temp.

Is your boat thru transom exhaust or thru prop?

Also the first place gear teeth fragments will go is into the upper bearing carrier as that is where the gear oil circulates.


My thoughts for now............
 
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