Twin Disc Marine Gearboxes

Mack Boring & Parts sells and supports Twin Disc gearboxes and parts. Twin Disc engineers more than 100 marine transmission models, from 35 to more than 4000 horsepower. Our advanced marine transmission technology delivers:
  • Quiet operation with helical gearing
  • Smooth, fast shifting with hydraulic, oil-cooled clutches
  • Full power and identical reduction ratios in forward and reverse
  • Minimal external plumbing
  • Down-angle output and remote or direct-mounted V-drive models
  • Renowned reliability and global after-sale service

QuickShift®–for a Smooth, Steep Power Curve

Experience the world’s smoothest, fastest shifting—plus amazing slow speed control. Quick Shift uses patented internal clutch actuation to deliver cushioned torque and optimum power in milliseconds, whether you nudge the throttle or go full out.

Brochures, Drawings, Installation Info & User Manuals

Please use the gear selector tool linked below. The gear selector tool is an excellent resource for all of your gearbox needs. It allows you to search by power output, ratio range, duty rating and configuration. Depending on what you enter into the search it will bring you a list of gears or the exact gear you searched for. Click on the the gear and all documentation on the gear will be listed and is downloadable. 

Gearbox Ratings

Up to 500 hours/year, low load factor usage planing hull vessels where typical full engine throttle operation is less than 10% of total time. The balance of operation at 80% of full engine throttle or less. Marine transmissions for use in long range pleasure cruisers, sportfish charter boats/patrol boats do not qualify for Pleasure Craft Service.

Note: Some revenue-producing applications such as Planing Hull Bristol Bay Gillnetter do qualify under Pleasure Craft rating definition.

Relatively low hour usage (less than 1500 hours/year) where full throttle operation is 2 hours out of 12. Typical
applications include planing hull vessels such as fire boats, sport-fish charter boats and patrol/customs boats. This
rating is also applicable to some bow and stern thruster applications.

Hour usage of up to 2000 hours/year (for models MG(X)-5114 and smaller) and up to 3000 hours/year (for models larger than MG-5114) with 50% of the operating time at full engine rating.

Typical applications include planing hull vessels such as ferries, fishing boats, some crew boats, and also some displacement hull yachts as well as some bow and stern thruster applications.

Hour usage of up to 4000 hours/year with up to 80% of operating time at full engine power. This duty classification is for usage where some variations in engine speed/power occur as part of normal vessel operation.

Typical vessels include mid-water trawlers, crew/supply boats, ferries and some inland water tow boats.

For use in continuous operation with little or no variation in engine speed/power settings.

Typical vessels include fishing trawlers, tow/tug boats and ocean going vessels.