72 johnson 50 hp no forward

[dantheman8302]

72 johnson electric shift wont go in forward, but i think my shift diode is bad also could that cause both no shifting and the clunk into gear when you shut off and where can i get a shift diode Thanks!!!!!:

 

[F_R]

Re: 72 johnson 50 hp no forward

A little bit confused by your description. You say it won't go into forward, then you turn around and say it clunks into forward when you turn the key off. So, does it go into forward or not? OK, let's start with the basics. Your motor defaults into forward, that is when all else fails it goes into forward automatically. That's supposed to be a fail-safe-get-you-home-feature. If it's stuck in neutral it either is full of garbage (metal chips) in the lower unit, or it is somehow being fed voltage to the green wire when it shouldn't be (bad shift switch??). The shift diodes wouldn't be responsible for that.

The shift diodes are indeed there to supply voltage to the shift switch after the key is turned off and until the motor (alternator) stops spinning. That prevents the immediate shift into forward clunk as soon as you turn the key off. It will shift into forward as soon as the alternator is going too slow to put out any significant current. If the shift diodes are not doing their job, check them as well as the rectifier and the alternator stator. The alternator has to be working in order for the shift diodes to supply juice to the shift switch.

If you don't know how to check diodes and rectifiers, check back here.

 

[dantheman8302]

Re: 72 johnson 50 hp no forward

Thank you i have already tested the shift diode i believe it to be bad i have a manual and it showed to test resistance between wires purple/green and yellow and then switch contacts there wasn't any resistance either way, HOW DO YOU TEST THE RECTIFERS ???? When I am in neutral it will not shift into forward so how can i test the shift switch ?? or could it be the upper or lower solenoid in the lower unit ? Thanks for your help

 

[F_R]

Re: 72 johnson 50 hp no forward

'Tain't the solenoids, so forget that. Rectifiers are tested the same way as the shift diodes except there are more diodes to check in there. Disconnect all wires and Test grey to red, and switch leads. Test grey to ground and switch leads. Do the same stuff with the other grey (grey to red and switch leads, grey to ground and switch leads).

Best way to start testing the shift switch is to locate the blue and green wires back at the powerhead, where they go down into the lower unit. Leave the wires connected, but expose the terminals. Connect a voltmeter to the green wire, turn on key (don't start motor) and shift to neutral. Should be battery voltage on green in neutral. Shift to forward. Should be no voltage on green in forward. Should be no voltage on blue with any of the above steps.

To test reverse, connect to blue wire and shift to reverse. Should be battery voltge on blue in reverse. Connect to green and shift to reverse. Should be battery voltage on green also.

In other words, there should be battery voltage on green in neutral, battery voltage on both green AND blue in reverse, and NO voltage at all on either wire in forward gear. Remember, forward is default. It goes into forward when all voltages are removed. It is also in forward anytime the motor is not running.

 

[F_R]

Re: 72 johnson 50 hp no forward

O-o-o-ps Sorry, I got the colors mixed up. I should have written YELLOW instead of grey in testing the rectifier. Grey is the tachometer wire. Sorry about the confusion.

 

[dantheman8302]

Re: 72 johnson 50 hp no forward

By the way thanks for all the help !!!! I tested the rectifiers it's fine, but when I tested the shift switch no matter what gear i put it into the green always showed about 12 volts, and no voltage to blue . Could this be the problem

 

[F_R]

Re: 72 johnson 50 hp no forward

Absolutely. But before you condemn it, make the same checks at the switch itself to eliminate possibility of somebody has screwed up the wiring between the switch and motor.

 

[dantheman8302]

Re: 72 johnson 50 hp no forward

This might sound stupid but where is the shift switch located, the wires go down into lower unit, then at the other end of terminals they run to a large yellow connecter that leads to shift controls.

 

[F_R]

Re: 72 johnson 50 hp no forward

Switch is in the remote control, actuated by moving the throttle lever.

 

[dantheman8302]

Re: 72 johnson 50 hp no forward

thanks i figured so , so i went ahead and pulled the shift controls apart and found it, i tested and the results were the same so i think it is bad, are those expensive and where could i find one quick because we wanted to go for some walleye over labor day hopefully, i am going to try some local boat shops but if you know any good dealers let me know. Also could the shift diode still be bad or could the switch being bad also cause the motor to jolt into gear on shutdown.

 

[F_R]

Re: 72 johnson 50 hp no forward

Have tried my best to lead you through this from a distance. There is always the possibility that somebody has screwed something up in the wiring that I can't see from here. And not meaning it as an insult, but you obviously have limited knowledge about electrical circuitry and testing......but that's OK. I am just saying this because you are at the point of buying some expensive parts.....parts that are not returnable if they do not fix the problem. There ARE benefits to taking it to a qualified shop and letting them fix it.

If the shift diodes test bad, theyre bad. If they are bad, it will jolt into gear instantly when turning the key off. I still am a little confused about the inter-reaction with the other problem you are experiencing.

A local Johnson/Evinrude dealer is the place to start for parts, he may have it on the shelf if you are lucky. There are a few on-line sources that are good too. ishopmarine is one, Sea Way marine is another. I am sure there probably are others.

 

[Texasmark]

Re: 72 johnson 50 hp no forward

Just adding a tidbit that you probably know. That gearbox failsafes in F.....meaning F is the no power position. The clunk you hear when you turn it off is it goint into F when you kill power.

This says that you can't keep power off the solenoid in your current condition. I assume that the diode you are talking about is between power and the solenoid such that the shorted (assuming) diode keeps voltage on the solenoid and will not allow it to deenergize and allow you to go to F gear when you select F.

Mark

 

[F_R]

Re: 72 johnson 50 hp no forward

Just for the record, the shift diodes under discussion are the encapsulated diodes at the main terminal wiring strip on the powerhead. Part number 384225.

It is actually two diodes, each connected to one of the two yellow wires coming from the alternator. The common output from the pair goes to the ign/battery side of the shift switch in the remote control.

The ignition switch is the primary feed to the shift switch. But when the key is turned off, the shift switch immediatly loses it's power source and the motor instantly jumps into gear with a very noticeable clunk.

The shift diodes pair prevents this by suppling a secondary source of power to the shift switch, that secondary source of power being the alternator....as long as the alternator is spinning there is a source of power via the diodes pair to the shift switch to keep the neutral solenoid actuated. As soon as the alternator coasts to a stop, the secondary power source no longer exists, the neutral solenoid is no longer activated, hydraulic pump pressure is no longer supplied and the motor defaults into gear.

 

[Texasmark]

Re: 72 johnson 50 hp no forward

Ok, these aren't special shift diodes, just power supply rectifiers to rectify the alternator's output that recharges the battery............:/

Mark

 

[F_R]

Re: 72 johnson 50 hp no forward

True, nothing special about them other than adequate voltage and current rating.