Driveline Vibration Bravo III

[Texas Ray 72]

Hi Everyone,
We own a 2004 Sundeck 220 with the 5.0mpi / Bravo III combo. On our last outing of the season in '22, I was towing a 2-up tube pushing the boat hard. As I was nearing the end the run the boat made a jolt/bump (hard to explain). After slowing down I thought I felt a slight vibration. As I went to put it on the trailer, it felt like it was struggling. Not it's usual self. Fast forward, just before this season I took it in for its usual every other season service...service the outdrive, check gimble & bellows, fuel/water separator, water impeller. I took it to a very reputable shop in San Antonio, no issues found, another clean bill of health. Brought it home, changed the oil & filter and started it on muffs...again no issues... running smooth as silk. We took the boat out on Friday for the first time. I immediately felt a significant driveline vibration as soon as it went into gear. I throttled up and the boat struggled to get on plane. The vibration was less noticeable than at lower RPM's but the boat was running at least 1000 rpms higher than normal to achieve cruising speed. I brought the motor back to idle and put it in neutral, vibration completely disappeared. Keeping it in neutral I run the motor up 3-4 thousand rpms and watch it. Smooth, no issues, no vibration, no missing, no sputtering...just like it always runs. I bring the boat back and trailer it. After a visual inspection of the props I only discover a small knick in the leading edge of the forward prop. I'm at a loss as to what could be the issue. I would have thought an outdrive service would have revealed if there was a gimble or u-joint issue. Could anyone provide some insight? It would be much appreciated..

 

[scoflaw]

Sound like your down a cylinder or 2. I'd start with a tune up/

 

[aerobat77]

Sound like your down a cylinder or 2. I'd start with a tune up/

That has nothing in common he is at least 1000 rpm higher to reach the same cruise speed i guess.

That points in the direction of a slipping clutch or similar.

 

[paulswagelock]

My first thought would have been a prop strike and a deformed blade. You sure there is not a bent blade?

 

[Nater Potater]

Unsure about the BIII's, but the earlier outdrives have a rubber cushion in the prop's hub that could go bad. Hopefully, someone more in-the-know will chime in on that as a possibility.

 

[Espos4]

Unsure about the BIII's, but the earlier outdrives have a rubber cushion in the prop's hub that could go bad. Hopefully, someone more in-the-know will chime in on that as a possibility.

Bravo 3's do not have a rubber hub. The props are splined directly onto the shafts. I think you'd have a hell of a bent prop to cause the symptoms he's having.

 

[BillK2632]

That you actually felt something "break" and then the vibration poor performance started and that you are not seeing any obvious damage on the props (BIII props don't have a rubber hub). That and the symptoms would lead me to look at the engine coupler.

 

[Texas Ray 72]

That you actually felt something "break" and then the vibration poor performance started and that you are not seeing any obvious damage on the props (BIII props don't have a rubber hub). That and the symptoms would lead me to look at the engine coupler.

I don't believe that the prop is bent, I'll look even closer but I'm about 95% sure I don't. Like I said, very minor knick in one, maybe 1/8 of an inch and not deep. Most likely I churned a rock up in the shallows and caught it. I could certainly see a worn coupler. The boat is 20 years old.

I probably should mention that when the boat is out of water running on the muffs, I put it in gear and did not feel the vibration. Only once in the water under a load is it noticeable

 

[BillK2632]

I don't believe that the prop is bent, I'll look even closer but I'm about 95% sure I don't. Like I said, very minor knick in one, maybe 1/8 of an inch and not deep. Most likely I churned a rock up in the shallows and caught it. I could certainly see a worn coupler. The boat is 20 years old.

I probably should mention that when the boat is out of water running on the muffs, I put it in gear and did not feel the vibration. Only once in the water under a load is it noticeable

Pointing even more to the coupler. The coupler is the connection between the motor and the outdrive input shaft. Very similar to how a car motor connects up to the transmission. It is a rubber bushing with a splined shaft in it - when failed or failing it is very similar to a transmission slipping in a car.

 

[Texas Ray 72]

Pointing even more to the coupler. The coupler is the connection between the motor and the outdrive input shaft. Very similar to how a car motor connects up to the transmission. It is a rubber bushing with a splined shaft in it - when failed or failing it is very similar to a transmission slipping in a car.

So they will produce a noticeable vibration when failing?

 

[BillK2632]

They can, the more common is slipping due to the rubber bushing tearing apart. Maybe there are others here that know, but I don't know exactly how to diagnose other than getting in there and looking at it - it's not an easy thing to get to, engine has to come out to replace. But your symptoms, vibration and more importantly the engine revving like something is slipping point to:

1. Spun prop hub (we know BIII's don't have rubber prob hubs, so this is not it)
2. Drive problem - ie cone clutch, gear damage. Does the drive shift normally?
3. Engine coupler.

Not suggesting you dive into replacing the coupler without more diagnosis, but if your drive checks out, shifts ok, fine at low speed, no metal particles in gear lube and not burnt, then that starts pointing to the coupler. Have you pulled the drive, verified alignment, checked the gear lube condition? Mis-alignment will lead to coupler failure.

 

[Texas Ray 72]

They can, the more common is slipping due to the rubber bushing tearing apart. Maybe there are others here that know, but I don't know exactly how to diagnose other than getting in there and looking at it - it's not an easy thing to get to, engine has to come out to replace. But your symptoms, vibration and more importantly the engine revving like something is slipping point to:

1. Spun prop hub (we know BIII's don't have rubber prob hubs, so this is not it)
2. Drive problem - ie cone clutch, gear damage. Does the drive shift normally?
3. Engine coupler.

Not suggesting you dive into replacing the coupler without more diagnosis, but if your drive checks out, shifts ok, fine at low speed, no metal particles in gear lube and not burnt, then that starts pointing to the coupler. Have you pulled the drive, verified alignment, checked the gear lube condition? Mis-alignment will lead to coupler failure.

Yes, shifts completely normal into forward and reverse. The outdrive was just serviced last month, new Amsoil Marine outdrive oil put in. The vibration begins as soon as you shift into forward. Its not a "Oh dear God...what the h*ll" vibration but certainly noticeable. Even my wife noticed it. It feels as though it lessens around 3000 & up rpms but again the boat is struggling. 35 mph at 5000 rpms. This is 10mph shy of what she normally runs on smooth water at these rpms. Not sure if this additional information helps or not.