Preventing Lower Unit Gearcase Failure

Preventing Lower Unit Gearcase Failure
Note broken teeth on drive gear caused by oyster reef.
We have seen quite a few lower unit gearcase failures in recent months and the majority of these could have been avoided with better understanding of how the gearcase works.

Shifting from neutral into forward or reverse is usually done without thinking but the way it is done is very important, and a crisp shifting motion is the best. A single lever binnacle control (combination shifter and throttle control) is designed with 5 of travel between the in-gear positions and throttle engagement and this allows the operator to advance the throttle carefully after the shift is made. The operator that gently nudges the lever during shifting for fear of "goosing" the throttle could be unknowingly creating premature wear and damage.

Shifting too slowly into and out of gear produces a "bumping" effect on the clutch dog and also the forward or reverse gears. This can sometimes sound like "ratcheting." A crisp shift produces only a clean "click" when the gears engage. Every audible bump-bump-bump or ratcheting sound is taking metal off the square edges designed into the gear teeth. The accompanying photos show rounding of clutch dog teeth that slow shifting creates a primary reason for difficulty shifting into forward or reverse.

The second most destructive thing you can do to your lower unit is grinding through sand and oyster shell. The prop in the photo has a bent blade and has been sharpened by sand. The broken gear teeth are a direct result of this and the part you can't see is the bent prop shaft, which is a huge indicator of trouble ahead.

Pay attention to your prop, check frequently for deep nicks, gouges and bent blades. Spin it and check for wobbling, (watch the sharp tips.) Have it inspected immediately if it does not run true. Change lower unit lube every six months and pull the prop and check for fishing line wrapped on the shaft every month.

Have a great season!

Chris Mapp

Coastal Bend Marine
Port O'Connor, TX