[OMC-Boats] OMC HYDRO-ELECTRIC LOWER UNITS

OMC introduced a new lower unit in 1968 on it's then-new 55-hp 3-cyl outboard. In 1969, they used a larger version gear case on the V-4 outboards. Eventually (1978) these units were adapted to OMC Stringer I/O's.
There are no-doubt members of this list running these "Hydro Electric Shift" OMC outboards and I don't want to exclued them from our recent on-going discussions.

Someone suggested borrowing the remote controls from these later outboards and using them for a parts source. That may be possible, I just haven't tried it.
Without studying an OMC wiring diagram, I wouldn't want to say for sure. And the mechanical switch design is most likely, still prone to failure.

I do know the OMC engineers' control "logic" took a major "C-change" and I thought the background theory would be worth sharing.

For some reason, OMC engineers decide to incorporate a fail-safe, "locked-in-forward" approach in the event of electrical or hydraulic failure.
In other words, FORWARD GEAR, NOT NEUTRAL became the default gear position, and you'd always get home safely?
And no more wind-milling props on the back of fast moving trailers.

The shifting setup of the lower unit is what OMC called their "Hydro Electric Shift", which is quite complex, consisting of voltage being applied to solenoids in the lower unit which in turn,
 change oil passages via a hydraulic oil pump that supplies various pressure on a spring loaded shifter dog. Makes you appreciate the "KISS? simplicity of our pure electric shift design.

The wires leading to the lower unit (at the powerhead) are still "Green" and "Blue". But now, the engine must be running or cranking over in order to shift OUT OF FORWARD GEAR.

With Hydro Electric Shift units,

In neutral, your remote controller supplies 12v to the "Green" wire.
In reverse, your remote controller supplies 12v to both wires, the "Green" one and the "Blue" one.
In forward, the remote controller supplies no voltage to either wire. (And the spring-loaded shifter dog forces the unit into forward gear.)

To check the lower unit for proper shifting AND to make sure you have no trouble there, remove the spark plugs to avoid problems and to allow a higher cranking speed with lower compression.

This next step eliminates the actual remote control shifter switch, in case problems may exist there....and allows you to focus on checking the lower unit operation.

Disconnect the blue & green wires at the knife connectors (the rubber insulated boots) leading to the lower unit at the powerhead,

Then using jumpers, take voltage direct from the starter solenoid to apply voltage to the "Green" wire for neutral, then both wires 'Green" & "Blue" for reverse.
(Remember the engine must be cranking over in order to shift. You may crank the engine with the key switch or by energizing the starter solenoid with a jumper wire).

With no voltage applied, the unit should be in "locked-in" forward. No need for a ground jumper... the lower unit's already grounded.

Lee
Received on Monday, 24 August 2009