1975 70hp Johnson tranny slipping to neutral

[gsf35099]

Newbie here,

I have a 1975 70hp Johnson that shifts in gear fine (both forward and reverse) but as the rpm start to climb it acts like it slips in to neutral and the engine just rev's up. Put the throttle/tranny handle back in neutral then back in to forward and the tranny locks again until you try and give it fuel.

I search the forum and only found one thread that mentioned this problem (actually the exact same problem )

My son adjust the transmission shaft and it appears to be adjusted right, but I just don't know. I read that the prop hub could possibly be spun, but I do not understand what that is.

Engine is on a tri-hull 1975 15' Glastron and was running great until just this morning.

Thank you for any help in troubleshooting.

 

[tashasdaddy]

Re: 1975 70hp Johnson tranny slipping to neutral

the prop has an inner and outer hub, with a rubber bushing between them, when the prop gets old, the bushing finally goes, allowing the inner hub to spin, with out turning the outer hub, that has the blades on it.

 

[gsf35099]

Re: 1975 70hp Johnson tranny slipping to neutral

So the inner hub will allow the outer hub (prop) to spin at low RPM's or less pressure (force) allowing the boat to move (idle or a little faster) and then stop spinning the prop at high RPM's or more force on the prop?

So since the engine and tranny seem fine, is it just the prop?

I just looked at another prop I have in the boat and see the rubber boot your talking about and think that if I just replace the prop, we should be good to go.

Thanks again for the help.

 

[tashasdaddy]

Re: 1975 70hp Johnson tranny slipping to neutral

if you have another that will fit, give it a try. you damaged prop can be repaired.

 

[gsf35099]

Re: 1975 70hp Johnson tranny slipping to neutral

if you have another that will fit, give it a try. you damaged prop can be repaired.

Thanks a bunch. That is probably all it is. The prop is the original and I'm not sure the original owner ever had it rebuilt and I sure haven't done anything to the prop's since I bought the boat from him 19 years ago..

Thanks again for the help.

 

[gsf35099]

Re: 1975 70hp Johnson tranny slipping to neutral

Thanks, tashasdaddy.

Different prop did the trick. I love these forums as they have helped me repair all kind of vehicles.