Alpha One "bump" when under load, fine when not in gear

swinds00

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Jun 2, 2011
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Mercruiser 350, Alpha one outdrive (late 1980's). Just had the motor/engine aligned and outdrive installed. After launching at idle going to the slip I could feel a thump in the driveline every once and a while (30 seconds or so), as if you hit a log underwater. Does it at any speed. No engine skip. When NOT in gear, it does not make the thump at any tilt level or steering pitch. No abnormal noise in the driveline (thru hull exhuast, so listening with ear to hull at idle not in gear) When underway at higher speeds you can see a "bump" in the prop wake when the driveline binds or slips. I will be pulling it out of the water hopefully this weekend after completely adjusting the shift cables (it was shifting fine, but its worth a try). Possible causes: U-joint, gimble bearing, bad lower? The drive was supposedly rebuilt..... If anyone has had a similar problem, or needs more info please let me know. Would like to get an idea before diving in.
 

Bondo

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Apr 17, 2002
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Re: Alpha One "bump" when under load, fine when not in gear

The drive was supposedly rebuilt.....

Ayuh,... Welcome Aboard,...

Drain the oil from the drive, 'n look for Metal...
 

Bt Doctur

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Aug 29, 2004
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19,092
Re: Alpha One "bump" when under load, fine when not in gear

last one I did was a broken tooth in the lower
 

swinds00

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Jun 2, 2011
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Re: Alpha One "bump" when under load, fine when not in gear

Thanks for the replies, something in the lower is what I am leaning towards, under no load and not in gear everything seem fine. I'll take it out and pull the drive oil and see what happens. I also have 2 spare pre-alpha 1.5 outdrives. From what I've read even with the pre-loaded lower it would bolt to the alpha upper? Thanks!
 
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