OMC Cobra lower unit shifting trouble

OMC Cobra lower units gearcases shifting problems

Last updated on 11/15/2023

Lower unit shifting problems
Engine rpm to high
Shift cable stretched
Shift rod seal full of corrosion
Motor rpm to high
Controls to engine compartment shift cable
Old style detent without update
Technical phone support is available

So you need help with your lower unit that has shifting problems

Hi, I’m Wayne Coll from Boatparts.ca tech service please note that the information put forth here are my own opinion based on repair work done over the last 30 years.

It’s not my intention to sell product or tell anyone how to do their own repairs. At the age 73. I know how the younger generation has a tendency to know everything. This is due to fact that at one time I was just like that, its amassing just how dumb 50-year latter will make you.

We are putting this page together to help out boating enthusiast interested in performing their own repairs.

I understand that many boaters starting out would not be able to afford a boat if they couldn’t do their own repairs. The best advice I can give you is slow down and don’t try to have every repair finished in a day.

Engine rpm to high

Boaters often turn up the engines carburetor to keep the motor running. Reason being, when old gas stored in the fuel tank is allowing the condensation to attack the gas, lowing the octane.

When fresh gas is added to the tank ,octane and rpm are then too high. The proper engine rpm is listed in your manual, that said in most case the following recomondaion can be used. V8 (550 rpm), V6 (625rpm) and four cylinder engines (650-675 rpm).

Shift cable stretched

The outdrives shift cable can become stretch when the following scenario can take place.

RPM of engine is to high usually above 750
When a stainless steel prop is used and moved from forward to reverse to quickly this will often chip the clutch and clutch-dog area of the gears
When the carburetor return spring is not working. Often I have seen door type springs added to help the boat side shift cable return to proper idle location.
Boat side shift cable can stretch or plastic shift levers are worn or broken. This will change the engine shift cable position. This is a common house boat problem when cable 30 plus feet.
When you have fishing line on prop shaft
Gasket compound was not used on mounting gasket
Shift bellow installed without bellow cement
Shift cable has not been change in 5-7 years (installed with out update)

Old style detent without update

There was an update in 1992 to the detent and spring located in the lower unit forward gear retainer. I will try to put a link so you can see what it looks like now. The shift detent and spring-ball on updated units have 2 step instead of one. This now making it easer for shift rod to move and making it easier to find neutral. Now shifter rod can be set with 8 turns or 7.156″ from base to top of shifter in neutral. Properly install shift rod should move into forward position with just one finger.

O-ring and wiper seal frozen in shifter cover

This is a common problem i have seen in Florida and other southern state where there is a buildup of some thing in the brass guide, wiper seal and the O-ring. This 5/16 ” O-ring can stop the shaft from moving at all. Note wiper seal and O-ring are included in lower unit seal kits.

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