1972 Johnson 25 horse slipping...

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chrispbrown27

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From time to time when running at varying speeds the motor will act as if I hit a stump, kicks up out of the water and the rpms scream. After it settles down I have to put it in neutral and then back into forward and then it runs fine until it happens again. Originally I thought it was the clutch dog acting up but based on what I have read here and there the clutch dog going out will allow the gear shift to physically slip into neutral not just sound like it is in neutral. Anyone got any ideas of where I should start looking to get it fixed up?
Chris
 
It doesn't jump completely out of the water, but it does kick up which could be from the forward momentum of the boat and not from the slipping. I don't believe that the prop is slipping but I have not marked it to make absolutely sure. The guy I bought the motor from said he had recently had the clutch dog replaced so I am leaning toward that not being the issue. As far as the prop goes, I have heard that with this year motor the prop hub has to be pressed out and a new one pressed in...does anyone have any experience with this?
Chris
 
my 72 Johnson 20hp was doing the same thing... guess what it was - clutch dog... He could have replaced the clutch dog, but it could be whatever the clutch dog engages that has a bad tooth on it or something.
 
Clutch dog it is! It slips outta gear, the motor lays back a bit and when the Clutch Dog catches again, it drives that lower unit into the transom with a Vengeance.

I fixed mine with a Dremel tool. You can buy the parts still.
Look at the inside of the Fwd/Rev gears for other damage.
 
How hard/easy is it to do this on your own? Looking at all the parts from exploded diagrams it looks like a real good way to losing some very important parts!
Chris
 
There's only a few, maybe 5 or 6 moving parts down there.
It's your Micrometer eye that will point out the problem when you get the parts out in your hand.
A mechanic in an outboard shop, with parts in hand, would have the job done in 45 minutes.
So the Hacker working off the Transom of his boat would take a bit longer. Like two days longer.

I can't imagine that happening in such a low HP motor. You might look for a strained shifting fork or similar that allowed the Dog to go 'partly' in gear.
There's a Connection between the upper and lower shift rod. Make sure that's well fastened.
 
Wouldn't trying to shift when the rpm's are too high do this also? The boat was used exclusively for duck hunting before I bought it and I can see this happening a lot when you are chasing a bird down or fighting to get out of a tight spot in flooded timber, in fact I have done it myself with other motors.
Chris
 
Appreciate the help man. I will start tearing into it next week after duck season ends. Gotta have it back in shape for the spring crappie bite!
Chris
 
Okay....have read through the replies on this...........
Lets start simple.
There is an adjustment that has not been mentioned by any one of the replies yet.
At the base of the shift handle you will see a fastener that goes through what looks like a crescent shaped slot. This is the adjustment.
Loosen the fastener and adjust the gearcase in forward gear to the point that you can feel drag at the prop. The handle must be fully in the shift detent to hold the gearcase in this position. If this adjustment is not done you can go through 10 clutch dogs and forward gears if you want to.
I did a long write up on this a year or so ago for a guy having an issue. Look up my old posts and you will find it.
At this point I would say there is a strong chance you will still have to go in and replace both the clutch dog and the forward gear but I would darn sure adjust and try before going to all that work.
 
B-b-b-but I got close! :p
There's a Connection between the upper and lower shift rod. Make sure that's well fastened.


That was a good post Pappy. Looking back, maybe I had an easy one like that with a big Johnson 35 Hp way back in the 50's when I was just a yun'un and didn't know to look real close.
Imagine all the Money and time I took to fix a Minor adjustment.
An adjustment that could have come loose by some heavy handling.
 
Ok, finally got a chance to tear into the motor and from what I could tell the gears and clutch dog looked brand new (as they should have if the previous owner had replaced the clutch dog like he told me). What would I be looking for if the clutch dog was bad? There was only a tiny bit of metal on the magnet (I assume it was a magnet since the metal was stuck to it) and I didn't notice any wear to speak of on the gears. If it isn't the clutch dog and gears am I looking at a spun hub on my prop? Is there a way I can check this on my own?

Some of the pictures are a bit blurry, but I think you can see the gears and the clutch dog well enough to tell the condition. Take a look at them and tell me if they look ok to you.
 

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To check for a spun hub, see the pic I've attached. Run it until it slips and then check to see if the marks are out of alignment. A shop in my area can press in a new hub for about $20-$40 if memory serves me right.

The outboard can kick up out of the water if the prop stops spinning. If the boat is moving at a decent rate of speed and the prop stops pushing, the force of the water will bring the motor up.
 

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No broken teeth. I believe what you see is a combination of the grease and bad angle. The surfaces of the gears and dog clutch showed no rub marks or wear that I could see at all. They really did look brand new to me. I have been reading back through Pappy's posts and I am going to try the adjustment he mentioned and also mark the hub to check if the prop is spun. From what I read it appears to me that props that use shear pins and have no splines on the inside do not have the bushings in the hubs that result in a spun prop....am I mistaken on this?
Chris
 
I didn't take any pictures, but today I took it all apart and cleaned it up to to get a better look for wear. The teeth on the gears are in good shape and do indeed look like they are brand new. The portion, on both reverse and forward gears, that makes contact with the clutch dog had some rub marks though I wouldn't consider it excessive at all. The clutch dog is worn somewhat where it makes contact with the gears more then I would like, but it still appears that it should lock in. After reassembling it all, I made the adjustment that Pappy mentioned and could definitely tell a difference when it bottomed out. Just turning it by hand the clutch dog locked in well. At this point I am hoping for the best and will be able to give it a test run next week to see if it's working ok.
On a side note, I recently checked into replacement front and reverse gears and dog clutch and I was truly astounded at the prices. For just 3 parts, no labor just the parts....around $800! Dear god, for that price I could buy a lot newer motor without any big issues. As many old Mercs, Mariners, Johnsons and Evinrudes as are still on the water you would think the prices would be somewhat more reasonable.
Chris
 

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