1977 70hp johnson slipping in gear

[boatdumb]

It's me again guys. Well, I was having a problem with my boat slipping in gear at high rpms. We thought it was the hub in the propeller, we replaced the hub and we still have the same problem. Do you think it is the clutch dog? If so how much is one and how hard is it to replace? Thanks...

 

[blueboat1]

Re: 1977 70hp johnson slipping in gear

Are you sure it's slipping or could it be cavitation? I have a 74 70hp and I thought I had a bad prop hub, it ended up being cavitation when I would punch it. Does it do it at all speeds, all times or only when take off?

 

[Paul Moir]

Re: 1977 70hp johnson slipping in gear

If it were a bad clutch dog jumping, it would be violently slamming in and out of gear. It sounds and feels like you hit a rock hard.<br />I'm with Tin Can on this. It sounds like either your cavitating, or the prop shop messed up to rehubbing. You could have the prop tested, but it's far more likely your cavitating.<br />Is there anything protruding from the hull in front of the propeller?

 

[boatdumb]

Re: 1977 70hp johnson slipping in gear

there is nothing protruding from the hull in front of the propeller. what is cavitating? it only does it at higher rpms. when it starts slipping i let off of the throttle and then we just putt along again. it will go for awhile at the higher rpms before it starts. thanks for any ideas.

 

[K Hultgre]

Re: 1977 70hp johnson slipping in gear

Cavitating is basically the propeller has sucked in some air from either the engine trimmed to far up or mounted to high on the boat so the water flowing past it is disturbued. If you can, look at the cavitation plate (big fin above propeller)and see if it is lower than the bottom of the boat or just even.<br />Try marking the propeller outer assy and tube in relation to the hub so that if the hub slips the marks will no longer line up, nail polish works well.<br />When it starts slipping can you back off the throttle almost to an idle then go right back to high RPM's with out it happening immediately. I had one that would operate similar to yours which I believe the rubber would get hot when it slipped then by putting around for a while it would cool off and grab allowing faster speeds until you hit a good size wave then she would slip again and yes a clutch dog will make a big bang if it goes in and out of gear as previously stated.

 

[boatdumb]

Re: 1977 70hp johnson slipping in gear

i looked at the cavitation plate, it is even with the bottom of the boat. What now?

 

[rickdb1boat]

Re: 1977 70hp johnson slipping in gear

Try trimming the motor in at high speed if you have electric trim. Otherwise, lower the motor down one notch with the trim pin before you set out for the day. If it still does it, recheck the prop hub. It's one of the two. I'm with kevin on this one!

 

[boatdumb]

Re: 1977 70hp johnson slipping in gear

thanks guys, I just want it to work... I will try that, it will probably be later this week before I get back out on the water. So I should go one trim notch at a time untill I hit the last notch. I am going to mark the prop hub also. I'm not 100% sure that the hub was pressed all the way back in place. I know on the old hub the (i'm not sure what it is called) plastic washer between the prop and the nut actually slid up on the splines of the shaft, with this hub it will not go up over the splines on the shaft at all. Sorry this has become a long post. If you know about the washer I would love to hear what you guys think.<br /><br />Thanks so much ,<br /><br />Dawn

 

[rickdb1boat]

Re: 1977 70hp johnson slipping in gear

Should go up on the splines. sounds like somebody installed hub wrong.