Transmission or prop slip

[ScottJ]

Hello to every body im new to the forum.
I just bought a used 2006 24v with 6 liter, with 20 hours. I am in the process of working all the bugs out. The problem I am having is either prop slip/cavitation or transmission slip. If I accelerate hard from a dead stop the boat pulls great up to 4000 rpm. Then it slips and the engine revs. I am unable to get above 4000 rpm with out slipping wether I accelerate hard or easy. I just sucked the fluid out of tranny and replaced (fluid still pink, not burnt smelling). Then ran boat to warm it up, shifted into nuetral and immediatley checked and filled to full using this method. I got 1 1/2 quarts into tranny. Tranny capacity is 2 quarts, I dont know if I got it all out when I drained, or do I need to add more. Or is the prop slipping (acme 537)? I keep thinking that if the tranny was slipping it would do it on the low end under hard acceleration, not at 4000+ rpm. Any insight would be greatly appreciated.

[dom w. forte]

Check the flange and prop key ways , we have seen a few shear off the key way at the flange and it will pull and then start slipping.

[ScottJ]

Thanks: I will check them.

[talltigeguy]

How fast are you going at 4000 RPM?

[ScottJ]

My seedometer says 35, I don't know how accurate it is.

[boatwakes]

Your fluid should not ever be pink(Pepto pink), it should be red. If it's pink, there's water in the trans from the trans cooler and your gearbox is slipping for sure. Double check and let us know.

[ScottJ]

I finally got a moment to pull my prop shaft apart. All keys look good, no sign of slipping. And yes transmission fluid was red, no water in it. Fluid looked good. Any other things I should look at?
Thanks for the help.

[boatwakes]

Do you lose speed when it "slips"? Does the boat vibrate when it happens? If so, thats cavitation from the prop. Prop cavitation is VERY evident on the blades by "burning" or discoloration on consistent parts of the prop. What you'll see is a fairly even distribution of discoloration on each blade of the propeller in the same area. If you don't see that, it's transmission slip. Trans slip can be caused by a clogged pickup filter or faulty pressure regulator, either of which won't allow enough hydraulic pressure to keep the clutch plates engaged. The extreme downside to trans slippage is if left unchecked, it can physically weld the clutches together and cause a locked condition in which the gearbox will not come out of gear and constantly be engaged in forward.
At this point, you need to run a pressure gauge on the cooler circuit to determine if you're loosing pressure. Choose a gauge that is greater than 250psi for this task and tap into the feed line to the cooler. Pressure should not exceed 200psi and not be below 160psi. Keep us posted.

[ScottJ]

Thanks for help so far. I took boat out this weekend. I have read on here about checking oil hot immediatley after shut down. I did this and still had slip, I read that the tranny capacity is 2 quarts and 1 1/2 quart gave me a full reading. I added another 1/4 quart and ran boat. Slipping seems to have stopped, but my dipstick now reads 1/2 inch above full when hot (boat in water) and a full inch above full cold (boat on trailer). Is this too much oil, will this cause other problems? I will get a T and a pressure gauge and check cooler line pressure this weekend. Also the slipping I'm experiencing is nothing like what boat wakes described as cavitation.
Thanks in advance for any help.