vacuum switch

[drhorsepower]

1969 55 hp electric shift. What does the vacuum switch on the side of the case near the throttle levers operate? is it for the electric shift?

 

[F_R]

Re: vacuum switch

Yes it is. When you turn the key off, the motor instantly loses electrical power to the shift switch, causing it to shift into forward gear, before the engine coasts to a stop. That gives an unnerving but harmless "clunk" the instant your turn the key off.

So.o.o.o, the vacuum switch senses that condition when the engine is still rotating and delays the loss of electrical power to the shift till it stops turning. Then it quietly slips into forward gear by default.

 

[coolguy147]

Re: vacuum switch

lol quietly there's no clunk just your imagination haha

 

[boobie]

Re: vacuum switch

Just listen to F-R. I've also worked on quite a few of them and he knows what he's talking about. F-R forgot to ad one thing. If you do get a "clunk" when you shut the mtr off you possibily have some thing wrong in your charging system.

 

[F_R]

Re: vacuum switch

Well, now that is very true. Depends on what year we are talking about. Later years did not have the vacuum switch. Instead, they accomplished the same result by connecting the shift through a couple of diodes to the alternator. The spinning alternator kept it in neutral till it came to a halt. If the alternator isn't working, it doesn't keep it in neutral, and you get the clunk. Depends on the year.

 

[boobie]

Re: vacuum switch

But, when they had the vacuum switch they didn't have the "monkey balls " your are talking about. As the OP stated he has a vacuum switch on it. "monkey balls" by the way was OMC service school terms a long time ago. Meaning diodes.

 

[seahorse5]

Re: vacuum switch

The other reason for the vacuum switch was so the motor would not start up if you were to turn the flywheel by hand with the keyswitch ON. That was an easy way to lose a finger or two if that happened.

 

[seahorse5]

Re: vacuum switch

"monkey balls" by the way was OMC service school terms a long time ago. Meaning diodes.

The other common name for them back then was "dog nuts"

 

[boobie]

Re: vacuum switch

The vacuum switch you are thinking of Seahorse was used on the '67 100 hp mtr for the reason you discribed and the mtr had to be cranking with the ign sw to make the pack fire. The 3 cyl vacuum sw had a different function even tho they looked the same on the 3 cyl's. There was an OMC service bulletin yrs ago describing the differences.

 

[F_R]

Re: vacuum switch

1968 and 1968 three cylinder 55hp motors had the vacuum switch for the reason I just explained. They did NOT have monkey nutz. Starting in 1970 and up, they DID have monkey nutz, but no vacuum switch. Simply a different method of arriving at the same goal.

The vacuum switch was used on a couple of 100hp motors to prevent accidental starting. That is a totally different function. It too, was replaced by an electronic safety circuit.