apollard

Have a problem that I'm preplexed about. Background: New to me 7.4L Bravo III drive. Only 200 hours on it, but the PO wasn't a sticler for maintenance IMO. Also my first I/O, but have had outboards for many years. The problem: it has a vibration when:

Turning under load or turning out of gear,
Vibration you can barely feel when under load going straight,
and no vibration when out of gear, unless the wheel is turned at least a full turn.

I pulled the drive, and the u-joints felt OK. The gimbal feels fine, no play, roughness - just smooth turning. Based on the symptoms, I replaced the u-joints anyway. They did have some mild marks on the cross, but not bad.

Reinstalled, and it was OK. However, within 20 minutes of running, the symptoms came back. Not as bad as before, but seems to be getting worse.

I'm going to replace the gimbal to see if that does it, but is there something else I'm missing?

ChristianGott

Is the engine coupler in good shape? if it's sketchy, it could let all the other stuff wiggle and wander....check the mounting bolts for tightness as well as the condition of the anti-vibration rubbers between the fky wheel and the coupler......

sunchaser796

REPLACE THE GIMBLE BEARING..IT IS BAD !!! The new bearing will not have a grease fitting hole in it.And when installing, make sure the open slits face the front of the engine and not the rear.Don't worry about replacing the zerc fitting with the supplied plug. Threads are different. make sure the bearing is fully in place and if possible check the engine alignment with an alignment tool. Good luck with it. Any problems pm me.

apollard

Coupler looks good, and barely any play between it and the splines, so I think it is OK. I'm going to change the gimbal bearing and will check the rubber isolators. Also get an alignment check tool from Whoya. Hopefully, that should take care of it. Thanks for the input - if it doesn't work, I'll be asking more questions.

apollard

OK, replaced the gimbal bearing - as before, vibration returns after an hour or so.

To recap, here's the issue:
Turning under load or turning out of gear,
Vibration you can barely feel when under load going straight - but the vibration is worse at full up trim,
and no vibration when out of gear, unless the wheel is turned at least a full turn.

Here's what I've done:
New U joints (old ones showed some visible wear, but felt fine)
New gimbal bearing (old one still feels fine), drive shaft o rings are in good shape and fit bearing tightly
Greased the splines (x2)
Checked drive alignment

Alignment is pretty close, but not dead on. The tool inserts easily, will turn easily, and is easy to remove (takes your whole hand, but not hard to remove). The alignment is dead on top to bottom, but off somewhat side to side (the stbd side imprints the spline pattern on the tool more then port). The rear engine mounts are tight and seem OK. Merc Tech manual says nothing about side to side alignment, just up and down.

Is the small alignment issue causing the vibration? If so, are the rear mounts bad (they look fine), or can the front mounts shift and cause this?

If not alignment, what? There's really nothing else to change, and the vibration disappearing after each change has me perplexed.

272bajadriver

iTrader: (1)

I have a bravo one outdrive and I was having the same problem unitl it gave out and my vibration turned into a lud clacking sound upon I immediately shut the boat off and idled back to shore. I replaced the u joints and the gimbal bearing and I will be installing the outdrive back in the boat tomorrow and it should have taken care of the problem. When I would turn it would vibrate until a couple of months later it gave out. My u joints looked pretty bad and were seized when I took them out so for me I think that was my problem. But im really surprised you replaced both the gimbal bearing and the u joints and your still having the same problem. Hopefully someone can chime in

toolsinbox

you could have a few things going on here. I would check coupler and also see if your engine is moving around on the stringers. did you rotate engine 180 deg. to check alignment?

apollard

Seems the coupler is cocked. The minor misalignment changes when you rotate the crankshaft. Time for an engine pull.