Force 1996 120 hp slips out of gear under load

[wncboater]

Hi,

Yesterday, while pulling the boat off the trailer, the motor didn't seem to pull very hard as I increased RPMs in reverse. In fact, we ended up backing the trailer further into the water to get the boat off. Putting it into forward gear, I idled out away from the boat ramp and throttled up to get on plane, I heard a gear slipping/grinding/ disengaging sort of noise, lost all power to the prop, while the engine revved way up. I slipped the throttle to neutral, came to a stop, tried again to get on plane with the same result. Experimenting some more, I found that the same thing happens in reverse; basically in forward and reverse, the engine shifts in to gear in a normal manner, and the boat will drive at low speeds normally, but if I give it much throttle (i.e. torque to the prop), the engine seems to "slip out of gear" and all thrust is lost.

Please give me any suggestions of ways I can diagnose and fix this problem, and thanks!

 

[timdan94]

Re: Force 1996 120 hp slips out of gear under load

I had the same problem with my 1985 85 hp force I took it apart and machined the clutch dogs down. It helped but when I try to tow a skier it slips out of gear

 

[wncboater]

Re: Force 1996 120 hp slips out of gear under load

I should add that it has never done this before, the motor has run very strong up through last weekend. Also, I changed the lower unit lubricant before taking it out this time with the recommended marine grade oil.

 

[bigbasser54]

Re: Force 1996 120 hp slips out of gear under load

I had a similar problem with my 97 120 HP Force, turns out I had just spun the hub of my prop. What type of prop are you running? Pull it off and check out the trust washer for circular scratches. If it looks like it is the problem and you are running a prop with a Flo-Torq II Hub then just purchase a new Flo-Torq II Hub Kit and install the entire kit into your prop. If you have a prop without a Flo-Torq Hub Kit you can have a hub pressed in for like $50, but you could get a brand new Aluminum Quicksilver prop and Flo-Torq II kit for like $125 it provides more flexibility if you ever plan on switching props b/c you can reuse the hub kit. If that is even the problem.

 

[algoboating]

Re: Force 1996 120 hp slips out of gear under load

i have the same prob whit my 95 120hp im thinking of replacing the clutch dog and gears but i dont know if its the same gears as a merc. I tryed a new prop new countrols oils

 

[kandil]

Re: Force 1996 120 hp slips out of gear under load

did you check the control cable for the shifting? is going in gear? maybe it is loos

 

[algoboating]

Re: Force 1996 120 hp slips out of gear under load

yes its not the shifting

 

[tjello327]

Re: Force 1996 120 hp slips out of gear under load

I had the same problem with mine. After getting into the lower unit (gears & dog) I found the driving face keys on the dogs and gears were worn (no longer a straight face.) I re-machined them with a dividing head at work. The material of the gears and dogs are heat treated steel so you must have the right tooling to do a precision job. If done correctly, it will work as good as new. Send a private message to me if you are interested in this repair.