84 Merc 90hp 6cyl slipping out of forward gear...

[444]

Had the boat out at the lake, during a medium left turn at it would momentarily slip out of gear, did the same at a bit of a harder right turn. Then the next day it started momentarily slipping out of gear during a straightline accel when trying to get the boat to plane. Throttle down a bit and it would go back into gear and I could throttle up again.

Where do I start looking? I plan to drain the lower gear oil and see if it's gotten water in there. If there is, would that cause it to momentarily pop out of gear or would it be something else? Boat was running/driving fine then this started happening this week.

 

[sxmerc]

Re: 84 Merc 90hp 6cyl slipping out of forward gear...

Are you sure it's coming out of gear and not a slipping prop hub instead? If it is coming out of gear, you have got a few things to check. Check gear oil first for evidence of metal fillings or metal pieces. If all looks good, check cable adjustment, and the cable itself to see if it's just stretched out, and or, has alot of play.

 

[Faztbullet]

Re: 84 Merc 90hp 6cyl slipping out of forward gear...

Sounds like hub to me............my $.02

 

[444]

Re: 84 Merc 90hp 6cyl slipping out of forward gear...

I ordered an OEM merc service manual for this thing today, hopefully that should help answer some of my questions. It could be prop hub slippage, I don't even totally know what that is so I can't say for sure what it is or is not. Could you please explain that? All I know for sure is it's a definite loss of forward thrust while the rpm jumps. I did rebuild my own big block v8 and transmission in my garage and in the process of restoring two muscle cars so I do know a thing or two about mechanics. Just trying to get up to speed on this outboard.

This problem has been getting progressively worse the last 3 times I've driven it. First it would just slip on a left turn. Then next time out left turn and hard right turn. Now when going straight as well. Any and all input is very helpful so I can decide how to tackle this.

 

[chum1]

Re: 84 Merc 90hp 6cyl slipping out of forward gear...

Hub slippage is the rubber inside the prop slips in the hub, try scribing a line on the back end of prop and nut then check and see if there still lined up after use or if its really loose put it in gear and you can turn prop with your foot, make sure its not running though

 

[444]

Re: 84 Merc 90hp 6cyl slipping out of forward gear...

If it is prop hub slip, what is the solution? Replacement of the prop?

 

[roncoop75]

Re: 84 Merc 90hp 6cyl slipping out of forward gear...

If it is prop hub slip, what is the solution? Replacement of the prop?

Or, hopefully, just the rubber hub, or insert, that insulates the prop shaft from the prop if you strike something solid, like a rock.

Take the prop off and mark the hub and prop with a line, then put it back on and run the boat at WOT for a while. Try a few hole shots while your out there. Come back home and take the prop off, if your lines don't match up anymore you've got a spun prop/hub.

 

[444]

Re: 84 Merc 90hp 6cyl slipping out of forward gear...

Or, hopefully, just the rubber hub, or insert, that insulates the prop shaft from the prop if you strike something solid, like a rock.

I can tell by looking at the prop, the previous owner did strike something solid with it on a prop fin. I can see where the prop fin was cracked and bent over, then bent back and hammered flat again. I did note it when I bought it however at first at least it did not seem to pose any problem. The slip issue has slowly been getting worse each time I've taken it out so the prop hub seems to be a good a theory as any.