9.5 Johnson 9R-72M Outboard Slipping?

[Lucenut]

Hi, I bought a Model 9R-72M Serial J3583959 outboard. It runs OK. Doesn't idle great, but with just me in a 14' john boat does 15mph.

But today I had 2 people and duck hunting gear and it started to slip I think. At first I thought it was cavitating. I would run the rpms back down to idle and accelerate slowly, sometimes back up on plane and then it would "slip" and lose power while the motor revved up really fast. My dad said he thought some motors have a slip-clutch type thing on the prop/lower unit instead of a shear pin. Could this be the case? How do you fix such a thing?

Could the lower unit be slipping? I have never rebuilt a lower unit, are parts available to rebuild an old motor like this? I read somewhere the 9R motors were from 69-73.

Thanks for any advice.

[Rebel Sympathy]

Your motor has a shear pin - factory term: drive pin. It usually either turns the prop or it breaks. Usually no in between. However, sometimes it will hold enough to turn the prop at idle. Check that first by removing the prop cotter pin, the prop nut and the prop. The drive pin will be behind the prop.

The hub in the middle of your prop may be slipping. If so, maybe it can be rebuilt at a prop shop.

The other possibility is that your gearcase is catching air and the prop is slipping in the air bubble. Cavitation is the term for that. That can be caused by a variety of things including a short shaft motor on a 20" transom boat, for example.

Your gears don't slip. They either work or they are broken. Sometimes a motor will jump in and out of gear if the dogs are worn. This rather violent and quite noticeable. The gearcase won't last long in that condition.

[Lucenut]

Hmm.

Thanks for the response. It's not coming out of gear I don't believe. At least I don't have to put it back into gear. I just slow the throttle and it starts biting again.

My first thought was cavitation. It is a short shaft. I tried trimming it up a notch and down a notch with no affect.

[Lucenut]

Replacemeny gears?

OK, I changed the lube in the lower unit and took a test drive. Still "slipping". Is there any way to get new gears for these old Johnson 9.5s?

[Rebel Sympathy]

Have you tried a different prop?

Did you check the shear/drive pin?

What is your boat's transom height?

I will state this again: Gears don't slip. They are gears and are engaged. This isn't an automatic transmission with fluid drive. Why did you change the gear lube? You may as well have changed spark plugs. Gears strip or break - or they don't. As I mentioned in my first response, the lower unit could be jumping in and out of gear. This is caused by worn dogs on the clutch dog and gears. This would be more of a series of jerks than a smooth slip.

If you want help, you are going to have to listen and provide better information.