# 20 hp Johnson bad clutch dog



## Earlo (Jan 13, 2014)

I have a 1973 Johnson 20R73A that has gear case issues. It was stuck in forward gear a couple of weeks ago. I tore down the lower unit and the forward gear and prop shaft were barely fused and were separated pretty easily in a press. The mechanic that did that for me said the shaft and gear should clean up with some emery cloth, which they did.
The other issue was that the forward bearing dowel had sheared off. I replaced the dowel, cleaned everything and got the gear case spinning again and reassembled it, took it to the lake and tested it for a 1/2 hour without issue. When I was loading on to the trailer, I unplugged the fuel line and was running the gas out of the motor. It was in gear, and pushing the boat against the trailer. Then I heard a single "THUNK". I backed off the throttle, shifted the motor a couple of times before it ran out of gas. All seemed okay.

This weekend I took it out again, and about every 30 seconds or so, when at more than 1/3 open throttle it would thunk and feel like I hit a stump. I tried adjusting the shift lever several times, but no luck. I took it home and took the lower unit apart, flipped the clutch dog around(one side has slightly less wear), and still the motor would clunk like hitting a stump when the rpms were brought up.

I'm pretty sure the dog needs to be replaced. My question is do I have necessarily have to replace the forward gear as well? The gear looks okay to me, certainly compared to the wear that the dog is showing. I found a new omc clutch dog and cradle for $107. The gear set is $385 which is more than I'm willing to dump into this thing.


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## SumDumGuy (Jan 14, 2014)

When I have read guys talking about the clutch dog thump they are always told to replace the clutch dog. From what I have read no one replaces anything else, and the problem is rectified.


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## Goldfish (Jan 14, 2014)

Was there any shims that would go in front of the forward gear that may have fallen out?


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## Earlo (Jan 14, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=338660#p338660 said:


> SumDumGuy » 42 minutes ago[/url]"]When I have read guys talking about the clutch dog thump they are always told to replace the clutch dog. From what I have read no one replaces anything else, and the problem is rectified.



Thanks. I ran up to a marine repair place with the gear case and had them look at it. They said the gear looked okay, but the clutch dog needed replacing. They actually had one in stock, but I found one on line for 25% less. Now awaiting shipment.


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## Earlo (Jan 14, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=338661#p338661 said:


> Goldfish » 20 minutes ago[/url]"]Was there any shims that would go in front of the forward gear that may have fallen out?



No, I don't think so. None are shown on the exploded diagram of the lower unit.


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## rwheadon (Jun 6, 2015)

I'm tagging along this thread for some advice from the pros and to provide additional "bruised" conditions to build the thread out a bit. 

I have the forward gear jumping into neutral at high throttle. It's quite frightening to be clipping along at a good pace and feel that jolt as it drops out of gear.

The standard failure I see is the clutch dog, but upon inspection my *gut* is that I need to also replace the forward gear.* I guess what I'm wondering is how the condition of my forward gear fares in comparison to others who have just replaced the clutch dog and been fine*. I have attached some annotated images below with attention drawn to the clutch dog and gear bruising. I have already purchased the new clutch dog and collar but don't want to put everything together if that gear is too compromised and will end up destroying the new clutch dog. So what do you think? Replace the gear or keep the gear?

This boat gets light use about 3 weeks out of the year so my guess is that repairing this correctly is going to be a far better choice than financing a new motor.

Thanks in advance for your help. 

rich
*Transmission*
















*Clutch Dog*




















*Forward Gear*


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## Johnny (Jun 7, 2015)

EXCELLENT presentation Earlo and rwheadon

I am the type of guy that will try the Old School of repairing it first.

if "only" the dog is chipped or worn to the point it needs replacement,
has anyone ever welded it up and redressed the surface with a grinder ?
Or, is that just prolonging the problem and probably asking for more damage
down the line.

Just wondering - - - as I am starting to hear the "clunk" on my 50hp Force.


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## rwheadon (Jun 7, 2015)

Well, to answer my own question... I need to also replace that bruised forward gear.

I stopped at a Johnson shop today in Walker, MN. The parts guy took one look at the forward gear and mentioned that it needed to be replaced since it would allow too much ramping under torque. He didn't have a gear in stock since he's more of a Honda/Yamaha shop now.





He also showed me that the newer (superceding) clutch dog is deeper than the original one by nearly 1/16" so getting a new forward gear matched to the new clutch dog is going to give a superior engagement than the original part. 





I wish I could afford a complete gear set, but we "git what we git and we don't pitch a fit" right?

Now I'm on the hunt for a forward gear locally available near Longville, MN so I can do some fishing!!

EDIT: 2015.06.08 : After talking to a few techs I decided to use a dremel and carefully grind away the ramping and fit my existing gear to the old clutch dog. I am flipping the clutch dog around so the bruised lobe hits reverse which is seldom torqued hard. I realize this is a temporary fix and have ordered a replacement gear which will arrive in a few weeks. I'll add a post on my results to the "custom fit" forward gear.

rich


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## rwheadon (Jun 9, 2015)

To bring closure to the posts I have added in this thread.

My Johnson 20 (20R73A) is running great and staying into gear just fine after grinding out the ramping that took place over time on the gear. 

* I used a dremel grinding bit (1/4" cylinder) to nibble away at the surface while keeping the configuration as close as possible.
* When the ramping was gone and I had nibbled about the same amount of material away from both contact points I used the dremel 1/8" polishing stone to slowly match the contact points to match the clutch dog lobes.
* I flipped the grooved side to face reverse gear since I don't hammer reverse as hard. 

I am remiss to say that I took no pictures in the process. 

I spent about 4 hours on the lake today and the motor did great. No popping out of gear in either reverse or forward. Once I get my gear set I will tear it down and install the new parts since it's only a 45 minute to 1 hr job at that point.

I appreciate the help from Longville Marine (Longville, MN) and Tim's Outboard (Hackensack, MN) for their help and patience as I worked through my ailing transmission.

So to bring my specific issue to a close, if your clutch dog is toast then your gear might be too. 

Tim's (https://www.timsoutboard.com) had three or four gear sets available but you would want to get the clutch dog from him too since he will make sure everything matches perfect before shipping to you. Since I had already purchased an OEM clutch dog I went another route.

rich


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