Drive line slipping 200-300 rpms? Spun coupler? 4.3 2001 Alpha 1

[Big6ft6]

Hi All, as title says my low-hour 2001 4.3L Alpha 1 combo is slipping under load, and seems to be getting worse. Under load the rpms will suddenly spin-up 200-300 with no boat speed change. Feels exactly like prop cavitation from weeds, but prop is clean.

I have two questions:

1) Can this be from an improperly adjusted shift cable?
2) Can I somehow mark the primary drive shaft at the engine coupler to check for coupler slip? I have a rear inspection plat at my transom that allows me to see and access the drive shaft right as it exits the bellhousing.

Here are other clues:

• If first noticed right after a lower unit service, new water pump, bellows job, new final shift cable, new tilt senders. (but not positive could've started before service and I just assumed it was weeds).
• No noise or clunking or grinding that I can hear
• I've marked the prop and prop drive shaft and no evidence of spun prop
• Happens under load, higher speeds, tubing, more passengers etc
• Has quickly gotten worse over a few outings
• No evidence of rubber or aluminum shavings near bell housing at back of engine
• I believe this is a newer/rebuilt engine, engine sparkly clean, and I found pieces of broken oil pan, and a half of a broken rod cap in bilge. Hours meters says 200.
• Engine starts and runs very well, no over heating or anything (yet), good compression, oil pressure etc.

 

[Scott Danforth]

1 no. Its a dog clutch drive
2 couplers dont spin and grab, they are either good or bad.

drop your trim to see if its ventilating

 

[Big6ft6]

Thanks Scott! Really appreciate your thoughts. This is my first sterndrive.

1) So if the rubber is starting to let go in my coupler, it wouldn't slip under higher load, and grab if I slow down? It seems to be getting worse, but maybe just because i had more people on the boat this last time.

2) This was my first thought, maybe trim senders were put on incorrectly, because it feels exactly like ventilating, like the prop is suddenly not "grabbing" water while I'm cruising. However, I've visually checked that when the trim gauge says flat/even, the cavitation plates on lower appear flat and even with hull/water line. What could've changed after my service that the prop would now be ventilating off/on while cruising even at neutral trim? Appreciate any thoughts.

 

[Rick Stephens]

As Scott stated, if your coupler is going out, it goes all the way. Not going to be an occasional problem. In fact, most times you end up with the driveshaft not turning enough that the motor overheats immediately.

 

[Bt Doctur]

have you checked the oil level in the drive?

 

[Big6ft6]

Cool, thanks Scott and Rick, I feel good knowing it likely isn't the coupler that was my biggest fear. But that begs the question, then what? If the prop isn't slipping, and the engine coupler is OK, what else could be causing the slip in the driveline of 200-300 rpms under load? It really does feel like prop ventilation/cavitation like the prop is losing bite with the water. But why suddenly is this occuring? This is my second summer with the boat, and I used it quite a bit last summer and this summer before this problem started.

Could anything have happened with the lower unit service that could cause this? I can't think of anything, but I'm not very experienced with the sterndrives.

again, here is what was serviced before this started happening.
1) new raw water impeller kit
2) new bellow kit: included bellows, gimble bearing, shift cable, and tilt sender service.
3) I also asked for general lower unit inspection because I was having a mild vibration around 1500-2000 rpms so I wanted them to look at U-joints, etc. I assume no-news meant they didn't find anything.

 

[Big6ft6]

have you checked the oil level in the drive?

Thanks Bt, no I have not actually checked oil on the lower unit, just visually inspected the drive-lube reservoir in the engine compartment. Could low drive oil cause this? What would be slipping due to low oil, I thought it was all gears in there? I'm going to run and check it now.

 

[Scott Danforth]

what else could be causing the slip in the driveline of 200-300 rpms under load? It really does feel like prop ventilation/cavitation like the prop is losing bite with the water. But why suddenly is this occuring? This is my second summer with the boat, and I used it quite a bit last summer and this summer before this problem started.

do you have anything in your boat you didnt have last year? do you have a cooler of beer up front you didnt have? are you running less fuel than last year? did you loose 50# and ditch your friends?

you may simply be on the ragged edge of venting....... and sometimes it just goes ppphhhhllllbbbbtttttt......

as stated, trim down, if the problem goes away, there you go.

 

[Bt Doctur]

 

[Big6ft6]

Thanks Bt, oil is good at boat top and bottom drain plugs. But for my curiosity, if the gears were melted smooth, would be able to go back in to drive by slowing down? I assumed bad gears would be either a go/no-go failure.

 

[Big6ft6]

do you have anything in your boat you didnt have last year? do you have a cooler of beer up front you didnt have? are you running less fuel than last year? did you loose 50# and ditch your friends?

you may simply be on the ragged edge of venting....... and sometimes it just goes ppphhhhllllbbbbtttttt......

as stated, trim down, if the problem goes away, there you go.

Thanks Scott, I'm going to mess around some more with trim. I didn't have anything different in the boat that I can think of. I did mess with the tilt when the problem was happening since it sounded/felt like ventilation and I don't think it affected it. It is hard to tell because when it happens my instant instinct is to come off throttle, not to mess with tilt. In my mind I picture damage happening like in Bt's photo of the gear set. But to be sure I'm going to get her out by myself so I don't have to have the pressure of my wife telling me to quit talking about the boat breaking down while we're out there.

 

[Scott Danforth]

pop the cover and look if you think it may be gears.

 

[Big6ft6]

Just for reference the last time out it got so bad I had to end the boat trip for fear I was going to fully lose forward motion. I couldn't pull the tube at all it was just slipping every time I tried to get up to speed. I usually pull tube with a slight negative trim to keep the hull down and provide better low-speed control. So I'm fairly certain the problem isn't lower unit position, however I'm still going to go out alone so I can spend some quality time with my girl...'er boat....and do some careful testing.

 

[Big6ft6]

Checked gears from the top inspection cover, the one I can see (horizontal entering from engine, the other is under oil) looks very nice and clean, oil looks clean/fresh.

Thanks everyone for taking the time to reply so far, I really appreciate your ideas/expertise!

 

[Rick Stephens]

If in doubt about the splines on the coupler you can pull the drive and look at it with a flashlight through the gimbal bearing, and look at the splines on the driveshaft to make sure they aren't full of metal shavings. Look at the rubber around the splined socket on the coupler as well. Melted and shedding rubber are bad. Takes a half hour or less to pull a drive, look and reinstall a drive.

 

[Searay205]

Exactly what happened to mine the coupler splines were stripping. I changed the shift cable (back in mid 90's) and being the dumb **** i am i cleaned the splines since there was gunk in between them. I reinstalled the outdrive with those splines so clean. So clean I didn't dirty them up with grease. 3 years later behind a 3.0 liter all they had to give. Really helps to read the service manual vs assuming you know something.....

 

[Big6ft6]

Exactly what happened to mine the coupler splines were stripping. I changed the shift cable (back in mid 90's) and being the dumb **** i am i cleaned the splines since there was gunk in between them. I reinstalled the outdrive with those splines so clean. So clean I didn't dirty them up with grease. 3 years later behind a 3.0 liter all they had to give. Really helps to read the service manual vs assuming you know something.....

SeaRay, when your splines were wearing out, would you say it first started "slipping", getting worse over a few outings, or did it just completely fail all at once?

 

[Searay205]

gradually worse then I pulled outdrive and looked in with flashlight they were gone. outdrive shaft was perfect. Again i had a little 3.0 liter pushing a 16 foot boat, i would imagine a v6 tear it up quicker. About 15 minutes to pull outdrive. Put in forward gear, remove trim cylinders (not hoses) just off back of drive, 6 bolts, heavy piece of cardboard to put under drive, gloves, weightlifting belt. lift off. Oh disconnect speedometer connections (3 seconds in front of outdrive) looks like a hose. Drive weighs 70lbs? but awkward.

I did my buddies yesterday to replace gasket. Drive off on, ck alignment no adjustment, 23 minutes

 

[Big6ft6]

well, I took her out this morning, and I think (crossing my fingers) it might just be ventilation. It may be that my tilt senders were installed slightly different during my recent lower unit service and so what is now showing as flat is actually just slightly trimmed up, just enough to cause prop ventilation when it wouldn't have in the past. I was able to get it to happen again, but if I trimmed it down just a touch I couldn't get it to repeat.

I'm still nervous because I'm surprised I never noticed even before that I got prop ventilation so easy with a slightly elevated trim. Prior to my lower unit service I would cruise slightly trimmed up, and I don't recall having this ventilation. But for now it seems the most plausible explanation so I'll run with it.

If it ends up being something else I'll update this post. Thanks to all for your input and advice, you're donation of time and experience is a wonderful example of community!