Rumbling Noise (Shaft)

A little more info would help here. There could be any number of probabilities that could cause a rumbling noise.

Is it in gear? At idle? What speed? What RPM? Does it sound like its coming from the engine, the tranny, or the running gear underneath? How many hours on the engine? Has this just started or has it been happening for some time?

More detail about the when and how it happens would help to determine where the possibilities are to find the issue.

was it low that the scientists told you to add? it sounds like your getting some type of deflection from the prop, check that the prop is tight on the shaft, of course check alignment and add it too your yearly maintanace schedule.
my first thought also was since the trans was replaced most of the time the mounts will get disturbed and the transmission is installed without re-alignment....take a close look at your cutlass bearings down near the prop...anyone of these could cause noises especially with the higher hours

Anthony, The first step in checking the shaft/engine alignment should be checking to see if the shaft is parallel to the cutlass bearing bore. Disconnect the coupling halves and see if the shaft moves in any direction (up, down, sideways). If it does and the prop shaft now turns freely, the engine is out of alignment. Disconnect the shaft stuffing box at the rubber hose/hose clamps and check the shaft again. Gravity will work against you at this point and the forward end of the shaft will want to hang down. I will place the foward end of the shaft on blocks of wood until I feel the shaft is parallel in the cutlass. This is sort of a judgement call and just feeling the shaft turning. Hopefully at this point the shaft is roughly centered in the hole in the hull. If not, then the strut needs to be aligned. If it is centered, now work forward and align the engine to the shaft position. The last thing to hook back up is the shaft stuffing box. Because it is held on with the rubber hose, it will center itself.

Go to work and keep us posted especially if you have a issue with the strut alignment.

Oh, the 1 drop every 10 seconds is good. Now is the time to get some Gox-tex packing in that stuffing box.

Chris, sounds like youre OK. The Goretex should drip a little less than traditional packing. If the packing is running warm, but not hot, then you should be fine.

Laker, you might want to verify that your prop is in good shape too. Even little nicks in a blade can cause vibration. You might be picking up weeds or something on one blade to cause vibration too seeing as it doesn't happen all the time. However, if it is happening with any amount of regularity, something else is probably wrong.

Check the alignment and verify if the cutlass bearings (or strut bushings)are good and if not replace them. They could very well be worn with that many hours. If the tranny was replaced, I would think that the strut bushings would have been replaced at the same time. At least that would make sense, but there are a lot of things some guys do that just don't make sense.

Let us kow how that works out for you.

Had a similar sound on my SN during the same conditions. We spent the better part of the season convinced it was related to a shaft problem. Turns out the swim platform was loose causing the rumbling noise. I would check that first. Who knows with a little luck you can fix it with a few bolt turns.

With ours, the rumbling seemed to originate from under floor in front of the rear seat. Forward from the true source.

Thanks guys!