GRRRR Sound. U-joints or Upper Unit??

[Stillskiing]

Greetings. I'm a long time boater new to the forums. Lost of great info here.
I've been using the forums to try and isolate a vibration that started on my Merc 260.
I've been getting kind of a GRRRRR sound turning the wheel and when the drive is all the way down.
When I get under way, I can feel the vibration and hear the sound. If I trim up just a touch, it stops.
But then when I turn either direction, I hear it again. This happens at low mid and high rpms.
From what I have gathered here, I headed for the U-joints. I pulled the drive and inspected the joints.
They all seem to be smooth and tight with no slop or play. I Have alot of auto experience and I have seen bad U-joints.
These seem to be totally functional. I did however, find that there is a little bit of play in the upper unit of the drive.
I can turn the shaft back and forth about a half inch or so before I see it engage the shaft connecting the lower unit.
I'm feeling like this should be a very tight tolerance and I may have a problem here.
If anyone can weigh in it would be appreciated.

1978 Tarva, 21' Daycruiser, 5.7 Merc 260, 260 Outdrive


Thanks

 

[zbnutcase]

Re: GRRRR Sound. U-joints or Upper Unit??

There shouldn't be any more than a few thousands of free play between the gears (backlash). I would pull the top cap off drive and look at the gears, they do burn up if its run low on oil.

 

[Bondo]

Re: GRRRR Sound. U-joints or Upper Unit??

Ayuh,... I agree with Zb,... But I'll add,...
U-joints on a drive can cause vibrations, even when they Feel/ Look tight....
When you pull the caps off,... You'll see ridges in the crosses...

 

[Don S]

Re: GRRRR Sound. U-joints or Upper Unit??

Probably time to pull the outdrive off and check for water in the bellows. The rust the water causes is usually the causes you are experiencing.

 

[Stillskiing]

Re: GRRRR Sound. U-joints or Upper Unit??

Ok now I feel a little silly. I go back out in the shop and start to tinker with it again. I don't know if it was just the light or what, but the Downward shaft is moving when I turn the main shaft. The upper does seem to be very tight and smooth.The play is in the Lower unit. Could the lower be the problem?Thanks for the response ZBnutcase,
Maybe some more words of wisdom??

 

[zbnutcase]

Re: GRRRR Sound. U-joints or Upper Unit??

I agree with what Bond-o added, as the joint operate at more extreme angles than in an automotive app.