OMC Cobra repair recommendation needed

[Dave R]

Originally Posted by 8gv

Waaaaay back in the day I had an OMC Cobra drive attached to a small block V8 in my Bayliner.

I recall having a shifting issue that was related to the shift interrupter switch(es).

My understanding is that the gears did not enjoy banging so the micro switches would interrupt the ignition and thus stumble the engine momentarily.

Mine was cured with a new switch or two.

Shift interrupt switch could be the issue, and certainly worth a test (just activate the switch manually and see if the engine stops), but there are some adjustments that could also be off. The switch is triggered by tension or compression on the shift cable when the drive won't go into or come out of gear. If it's out of adjustment, there's not enough movement in the W cam that activates the switch and it fails to trigger. This video has a lot of inaccurate information, but it does show basically how the system works: https://www.youtube.com/watch?v=whGSfsGHEao

I am 90% sure that full adjustment or testing of the shift interrupt (or ESA) system must be done in the water and with the engine running and the propeller installed. The shift dogs on the gears in these drives are back cut and require a load on them to make them mechanically "want" to stay in gear. If the boat is out of the water or there's no prop, it's impossible to load the gears.

Basically, the cable from the shifter (upper shift cable) only loads the spring in the shift mechanism which then transfers that load to the lower lower shift cable. As the spring flexes, it moves a cam that activates the shift interrupt switch and the engine's ignition system is grounded which stops the spark plugs from firing, thus making the engine rapidly slow down. When this happens, the load on the shift dogs in the drive disappears and the dog clutch immediately shifts in whatever direction it is being being pushed from the built up spring tension. When that happens, the cam on the shift interrupt switch returns to normal and the engine's ignition system is no longer grounded so the spark plugs start firing again. When it's working correctly, this all happens in milliseconds so you don't even notice the brief hiccup in the engine.

[SAB1]

Good luck. Try finding a small shop away from the lake. I’ve got a 1997 Volvo and some places just plain won’t on it as it’s “to old” I’ve been told. They plenty of work on newer boats.

[Donzi Minx]

I have had two of these stretched cables replaced on my Mercruiser. Dave's Motorboat Shoppe may be able to troubleshoot, diagnose, and repair.... he's the best!