Question for everyone.

Boat 2002 Cobalt 206
VP 5.0 GXi DP

I am getting a somewhat loud rumbling noise which appears to be coming from the drive area. Is bad when on plane and the drive is all the way down. If I trim it up a bit (again while on plane), mostly goes away. But during turns it comes right back. The noise is also there at idol and very slow speeds, no matter where the drive is positioned.

I have a guess as to what may be going on, but looking for thoughts before I turn it over to more capable hands.

Possible gimbal or u-joints.

How many hours?

about 300 hrs

Any noise in neutral?

"Any noise in neutral?"

Yes.

Possible gimbal, but 80% it's the u-joints. When the drive is all the way down, the joints are slightly bent. The drive must be trimmed up slightly for the input & output shafts to be parallel. Hence, the rumble goes away. And obviously the joints are bent any time you turn. The noise will appear at idle because the shafts are spinning slow enough that the joints can 'flop' a little. It also may be a sign the drive is slightly out of alignment to the engine.

Basically, it's time for about $500 worth of u-joint & gimbal bearing replacement and alignment service. ($500 is probably optimistic? Hey, it is a boat after all!)

Should be like brand new afterwards.

Yep, this is what I was thinking. Thanks guys...

u-joints.

I saw a guy at the ramp the other day loading his boat with the drive trimmed far enough out that the prop was almost completely in air. He left it running like that for about 2 minutes with the wheel hard over to starboard. I bet he has a u-joint/gimbal bearing bill in his future too. Try not to run the engine with the drive raised above the normal trim range when you can, it puts alot of stress on the drive.

I'm not suggesting you have done this, just passing along some info.

Mine was rumbling last year too. I took the drive off and could feel no roughness or looseness in the U-joints, but I spent $22 on new U-joints and put them in anyway. I inspected the old U-joints for excessive wear and could find nothing wrong with them. The gimbal bearing was perfect. I adjusted the engine alignment a little. It's quiet now. Guessing it was the alignment, though it was barely out.

Hi Dave:

I would think a slight alignment issue as you described would leave some telltale marks on the drive shaft as it vibrated in the coupler. I am wondering if you noticed any wear marks on the drive shaft?

Dropped the boat off, and per a message left with for me, they think its the "Transom Bearings". I assume that is shop talk for the Gimbal bearings???

Anyone know?

That is not any description of any parts of any VP or Mercruiser that I have ever heard. You need to pin them down, right now. Do they mean "a Gimbal Bearing or the Drive shaft U-Joint bearings?"

Already tried. That was just a msg I got when we got home yesterday, and shop is closed today, given that they all worked through the July 4th weekend. Have to wait until tomorrow to get more info.