There are a number of solutions for strengthening a stern drive’s components to reduce failures that have shown some limited improvement in reliability. And there are many complete swap-out solutions that can absolutely solve the reliability issue, but can be expensive and/or impact the boat’s performance or handling characteristics.

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The cause of many gear and shaft failures is the enormous torque spike that is generated each time the propeller exits, and then re-enters the water after hitting a wave.  These spikes are generated by the inertia of the rotating engine assemblies and can be 2X-4X the actual torque output of the engine.  Each spike lasts only a fraction of a second and throttling alone cannot eliminate them.  Every spike causes stress to the gears, shafts, bearings and propeller blades. Eventually, something is going to fail.

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DriveGuardian is a patented device (US 8,771,087) that replaces the Bravo rubber coupler or damper plate with a torque-limiting clutch that absorbs and dissipates the spikes. DriveGuardian eliminates the source of the damage instead of playing a losing game of trying to make each component strong enough to handle 4X the engine’s torque.  Because that is what it would take to make this issue go away.

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