slipping problem

[jamelvin]

My 1987 88hp Johnson Spl sounds the lower unit is slipping when it is under power. When it does this it feels as if it has hit something. I searched and found that it may be a worn clutch dog or a spun prop. My mechanic says the clutch dog is ok with no signs of wear (points are sharp). I tried another prop and it still did it. The motor is doing this at low rpm's not just at high rpm's. Mechanic says that it acts like the clutch dog is overriding the gears. My boat is a 25' Crest pontoon. Any ideas? thanks.

 

[JB]

Re: slipping problem

Have you investigated prop ventilation?

 

[Jack Shellac]

Re: slipping problem

JB may have it. If nothing is wrong with the motor, it may be cavitating trying to push this heavy pontoon boat. What kind of prop do you have? Has it worked OK before?

 

[BF]

Re: slipping problem

I've had this problem when the lower unit has gone bad on my 150 hp merc... I think it's the pinion gear on the driveshaft jumping a tooth on the forward gear. Could be a bad driveshaft bearing or a bad bearing on propshaft. Were there filings in the lower unit oil? BTW my clutch dog looked fine, but the gears were damaged.... Oh, ya, last time it was a twisted driveshaft that was the cause.<br /><br />Good luck.<br /><br />Brent

 

[jamelvin]

Re: slipping problem

I've had the motor about 3.5 years and it just started doing it the last year or so. I am running a stainless 14X17 pitch. Would prop cavitaion happen a low rpm's? Wouldn't cavitation cause the rpm's to spike (they're not)? I tried the boat out with a 14X13 composite prop to make sure I didn't have a spun prop. I got a lot of cavitation with this prop.<br />I checked with my mechanic and he indicated it wasn't the driveshaft/pinion gear recommendation. He also indicated that cavitation wouldn't cause this problem.<br />Any more ideas? thanks

 

[steelespike]

Re: slipping problem

If it was mine I would be looking in the gearcase<br />or possibly the shift rod/linkage.Did it always do it at slow speeds or did it gradually get worse?Check to be sure the remote shift cable is<br />getting full travel.If it developed over night <br /> could be in the shift mechanism somewhere between<br />the remote lever and the gearcase.

 

[Yepblaze]

Re: slipping problem

Sure sounds like a classic case of the dogs. Perhaps it's got excessive clearance in there somewhre or something like that.<br /><br />Maybe the dogs were fine when inspected last, but have since failed.

 

[jamelvin]

Re: slipping problem

It gradually got worse. It originally only did it at higher rpm's and became worse. The clutch dog was looked at (and changed out) a couple of weeks ago. The boat is coming out of the water next week to be looked at again. Hopefully something (cheap) will be found and fixed. thanks.

 

[jee70611]

Re: slipping problem

James,<br /><br />I had this same problem with an old 35 horse evinrude. It ended up not being the clutch dog but there was a shift locker that was missing. I don't know if yours has one, but look around for a spring loaded bar with a roller on it that would help hold the engine in gear. Steelespike beat me to it but if the clutch dog, gears, and bearings are good the only things that I can see that would make it do that is a bad locker or improperly adjusted shift cable. Did the mechanic pull the lower unit when he inspected the dog? If not, have it pulled and check the splines that go into the powerhead. They could possibly be worn down enough to slip. I don't see how though unless you hit something really hard before it all started, but it's possible. Good Luck and let us know how it goes.<br /><br />James

 

[jamelvin]

Re: slipping problem

My mechanic did pull the lower unit. I will pass on the info about the shift locker. If the shift cable was not properly adjusted wouldn't the motor shift and stay out of gear? This sounds like it has hit something but stays in gear. thanks.