New lower unit slips out of gear... i think

[mstrud]

i own a VJ50TLETB on a 20ft toon, i put a brand new lower unit on it two months ago. Ive been having an intermitant problem with it. It doesnt do it at an idle or anywhere on the low end, but when i get it about halfway open to WOT, it may run great for a few minutes maybe an hour but eventually itll get to the point where it feels like it slips out of gear and if you;re standing up without holding on you'll go flying foreward. I dont hear any grinding when it happens, which puzzles me. the motor doesnt nessisarily race either if so its only by about 100 rpm, it just keeps humming along but the boat definately looses thrust. I'm pretty sure i got the 21 15/16" +/- 1/32 shift rod height dead on, i put new control cables on it a month ago, i tried setting the shift cable short to make sure it;s well in the foreward position but changed that when it didnt fully engage reverse. the fact that it does it at 1/2 throttle cancels out cavitiation as i know for damned sure the foot is well in the water. Reverse works fine, although i dont run in rev nearly as much as F, but i have yet to experience this issue there. What should i be looking at?

 

[F_R]

Re: New lower unit slips out of gear... i think

So, it's doing this at half throttle? What does it do at full throttle, or is that impossible? Once it comes out of gear, what do you have to do to get it back in gear?

Actually, I have a hard time believing it is coming out of gear. You dismiss the idea of cavitation, but I highly suspect that your problem is cavitation/ventilation.

I suppose you have checked the prop hub by marking it, right?

 

[5150abf]

Re: New lower unit slips out of gear... i think

If it were coming out of gear the engine would race with no load on it, as FR said, probably cavitation.

That is where the prop starts sucking air which would giev you your loss of thrust.

Try taking some trim out of the motor, move the prop closer to the boat, you don't say if you have power tilt/trim.

If you do just trim it down, if not try dropping it down 1 hole at the transom

 

[mstrud]

Re: New lower unit slips out of gear... i think

It does it at any trim setting. once it does it i back off the throttle out of fear that i may be grinding gears, but it will keep doing it again and again, once it starts doing it it normally keeps the trend. the motor is on its highest setting but i feel that thats still to low of a setting as i get an assload of water shooting up off the transom, and the cavitation plate is about 5-6 inches under water. I guess ill get out the hoist and drop it a setting and see if that takes care of it.

 

[ezeke]

Re: New lower unit slips out of gear... i think

Maybe I missed some of what has been done, but did you set the shift rod to specification before mounting the gearcase? Also, have you tested the propeller to be sure it is not slipping:

The propeller can be checked by simply scribing a line across the hubs, using the cotter pin as a pointer and checking after you have the problem again. .

 

[mstrud]

Re: New lower unit slips out of gear... i think

i dropped the motor one setting, took it out for about an hour, it only did it to me once, could have been a random patch of floating lake weeds tho, or it could come down one more notch to totally fix it. so i rekon it was cavitation. But now there's even more water rushing up vertically past the motor, which is fine in a lake, but i prefer salt. Does anyone know if a jack plate with a set back would cure the excessive upward rushing water. I cant even see the **** stream through all the spray thats shooting up back there.