Lower Shift Cable/shift assist switch interaction???

[Limited-Time]

96 Mercruser Alpha 1 Gen II. Replaced the lower shift cable and adjusted the cables per the service manual. All is well again. However I would like to know (for my own clarification) how the cable linkageshift/ assist linkage interact together. After the replacement I watched the action of the shift mech. going both in and out of gear. The shift assist switch always triggered when going from in gear to neutral, from either reverse or forward. However with the engine off, the shift assist trigger bracket did not move when going from in gear to neutral. What gives????

 

[Blk-n-Blu]

Re: Lower Shift Cable/shift assist switch interaction???

maybe this will help:
http://www.iboats.com/bbboard/bbBoard.cgi?a=redirect;url=http://www.mercstuff.com/howdoi.htm

 

[Don S]

Re: Lower Shift Cable/shift assist switch interaction???

The ONLY purpose of the shift interrupt system is to get the drive out of gear when it is running and in the water with a load on the prop.
The lower gears (Both Forward and reverse) have dogs that engage the dog clutch. These dogs are reverse cut so the drive will stay in gear under heavy load, but even at idle, if the shift interrupt switches didn't work it would be very difficult to get the drive out of gear.
What happens when is gear goes something like this.
When you start to put the shifter into neutral there is resistance from the shift dogs, the outer part of the shift cable is attacted to the Y shaped, spring loaded bracket by the shift interrupt switch. When that y plate moves and activates the shift interrupt switch, the ignition is grounded and the engine dies due to lack of spark. With no pressure on the shift dogs, the inner cable then pulls the drive into neutral. When this happens, the Y plate releases the shift interrupt switch and ignition is returned and the engine keeps running.
All this takes a split second and if you really listen close, you can hear the engine drop a few rpm before running normal again.
With an old corroded cable, there is always pressure on the cable and the Y plate will not release the shift interrupt switch. Then the engine dies completely.
The system is NOT designed to work when putting the drive into gear. Even when the boat is out of the water on on muffs it won't operate because there is no back pressure on the prop to cause the resistance.

Hope that makes sense.

 

[Limited-Time]

Re: Lower Shift Cable/shift assist switch interaction???

Thanks for the responses. Don that clears it up for me. I could not find a tech here that actually understood how the system functioned. They all knew the adjustment procedures off the top of thier heads but none seemed to know how it actually worked.

 

[ziggy]

Re: Lower Shift Cable/shift assist switch interaction???

that was a good question l-t.... good answer too dons..... bet it helps me this spring when i'm hookin my cables back up......

The system is NOT designed to work when putting the drive into gear. Even when the boat is out of the water on on muffs it won't operate because there is no back pressure on the prop to cause the resistance.

that helped clarify the service manual for me... i thought that's what it said. but that statement convinces me....

there must be some serious pressure put on that outer cable to overcome the size of the spring on the y plate......

 

[achris]

Re: Lower Shift Cable/shift assist switch interaction???

The undercut on the clutch faces is 2 degrees... With a bit of load on that effectively locks them together. The force required to disengage, at idle, is high. Under power they might as well be welded together! I cringe whenever I hear that someone has disconnected the switch 'because it stalls the engine!'. Errr, that's what it was designed to do!!!

Cheers all..........