mercruiser 120 shifting problem

[ispurpleafruit]

I have a 1967 Chrysler courier with a 120hp mercruiser engine. I have been having problems getting the boat out of gear. someone told me about something called a shift interrupter switch. I adjusted the linkage to properly actuate the switch and it worked great for a couple of times out on the water but then it started happening again. When I run the boat off the hose and try to activate the switch by hand it doesn't do anything. So i put a continuity tester across the terminals and depressed the switch and sure enough the switch works just fine. Does any one know where the switch ties into my ignition system so I can look there for a problem. If anyone has any input at all it would be greatly appreciated. Thanks Andrew

 

[achris]

Re: mercruiser 120 shifting problem

One wire from the switch goes to ground, the other to the '-' side of the coil (same side as the points).

 

[libellav15]

Re: mercruiser 120 shifting problem

does it come out of gear when you shut the engine off?

 

[ispurpleafruit]

Re: mercruiser 120 shifting problem

yes, the stern drive does come out of gear when I shut off the engine. that's how I did it the last time out but in a pinch at a crowded ramp that is not fun. I have found some old dried up wire insulation in a few places and replaced what is bad but I don't really want to cut up the wiring harness to find the bad spot in the wire so can I just add a new wire from any ground to one side of the switch and from the coil to the other side of the switch??? if this is the only thing the switch operates then I don't think it would be a problem but if there is something else that I am not seeing then I will cause a hole other mess of problems by cutting the old wires and running new ones.

 

[achris]

Re: mercruiser 120 shifting problem

yes, the stern drive does come out of gear when I shut off the engine. that's how I did it the last time out but in a pinch at a crowded ramp that is not fun. I have found some old dried up wire insulation in a few places and replaced what is bad but I don't really want to cut up the wiring harness to find the bad spot in the wire so can I just add a new wire from any ground to one side of the switch and from the coil to the other side of the switch??? if this is the only thing the switch operates then I don't think it would be a problem but if there is something else that I am not seeing then I will cause a hole other mess of problems by cutting the old wires and running new ones.

That would work perfectly....

Chris.......

 

[swihartart]

Re: mercruiser 120 shifting problem

Does the engine stall when trying to shift to neutral?

I adjusted the linkage to properly actuate the switch and it worked great for a couple of times out on the water but then it started happening again.

If the new wiring doesn't fix it.
This could be an indication of a lower shift cable going bad.

When they start hanging up in the sheath from wear or age and corrosion they actuate the shift interrupt too long and it stalls the engine. The boat slips out of gear (assuming the shifter is in N) after stall because the load on prop is gone and the clutch dogs can disengage.

You can restart and shift fine a few times but no amount of adjusting will fix the problem and it just gets worse as time goes on.

$75 and about 3 hours it will end the frustration at the ramp when you can't shift without stalling.