Bravo III Outdrive "slipping"

[grouch0jr]

Hi all, new user here.

Twin 359 mags with with bravo 3 drives.

While taking her out yesterday I got up on plane, then almost immediately the starboard engine RPMs increased and the boat fell off plane. I made sure the drives were all the way down and tried a couple more times. I couldn't get back up on plane and stdb RPMs would shoot up, felt like it was "slipping" under load. I was able to limp back to the dock, and was able to use the both engines to maneuver while docking, although it didn't quite feel right.

Once tied up at the dock I put the drives in the trailer position and did the "reach around" to check the props. They were both in place and didn't seem fouled. I checked the gear lube reservoir and the level/color was not abnormal. I don't think its an outdrive probelm, it was a brand new SEI installed at the beginning of last season. I've read some threads that indicate it might be a failing coupler. I didn't smell any burnt rubber down in engine room. Is there any way to check the coupler while it is installed?

Also, any other ideas?

 

[kghost]

Start STB engine only. If you can look at very back of engine, you should see the drive shaft coming thru transom (about 1" or so in diameter) that shaft is what goes into coupler.
You should see that drive shaft spinning
If you dont then coupler is bad and engine will need to be pulled to replace.
Now if the shaft is spinning it may be touching coupler and will spin as drive is not under load. You can shift into gear with drive down part way but still have props visable and see if props actually spin.


Because Bravo drives use an engine mounted water impeller system so the engine and exhaust will still get water so there will be no burning smells. That occurs on Alpha drives as the impeller is inside and driven by the drive/coupler.

 

[grouch0jr]

Thanks for the reply. I just got back from the boat. I took a look at the coupler and did not see any debris or rubber dust. With the drives down I started stbd only and shifted forward/reverse several times. I was clearly getting thrust in each direction.

I also noticed that my stbd side trim reservoir was almost empty... I topped it off and got an oil slick out the back of the boat. So I think one of the trim lines may have ruptured. This is something I need to address, but I dont think its related...

 

[AllDodge]

I think the coupler tore

When was the last time the drives were pulled and alignment was checked? Most don't do this and after enough time things change

This is probably a large boat and if your one that runs the blower when running you may never smell rubber. Open engine hatch, have someone close to motor, put starboard in gear and increase throttle

 

[kghost]

Thanks for the reply. I just got back from the boat. I took a look at the coupler and did not see any debris or rubber dust. With the drives down I started stbd only and shifted forward/reverse several times. I was clearly getting thrust in each direction.

I also noticed that my stbd side trim reservoir was almost empty... I topped it off and got an oil slick out the back of the boat. So I think one of the trim lines may have ruptured. This is something I need to address, but I dont think its related...

The inside or Female part of the coupler is Aluminum splines bonded to a large rubber outer absorbing ring which is bonded to the aluminum housing. The shaft from the drive is Steel Male splines.
Two things can happen,
1. And most common, The female aluminum splines strip away due to lack of greasing and/or misalignment.
2. The rubber fractures and allows engine to spin and drive shaft will spin possibly but drive shaft does not spin under load.


Most likely the boat will need to be pulled out of the water and properly inspected and outdrive will have to be checked for mechanical failure and removed to see if Male splines of drive shaft are full of aluminum from stripping away at the coupler


see images

1. Coupler
2. Drive shaft from outdrive