Parts for Allison Marine MH

Having a boat that uses Allison Marine MH gears can be great — until it breaks down. If you find yourself needing Allison Marine MH parts for sale, you may not know what to do. These parts are not always easy to find unless you shop with Diesel Pro Power.

We are the only source you need for finding Allison Marine MH parts online. We have a huge selection of Allison Marine MH parts, bigger than you’re likely to find anywhere else, and we can get them to you right away, so you experience a minimum of downtime.

It’s true. We have every Allison Marine MH part you can think of and probably a few you hadn’t considered. We carry internal parts like gear shafts, springs, bolts, couplings, seals, washers, transmission bearings and rebuilt gears as well as products like oil gauges, marine controls, marine steering, cables, bulbs, searchlights, navigation lights and a lot more. If there is something you're looking for that you can't find, though, get in touch with us. We’ll help you track down the exact part you need or something that will work just like it or better.

Have a problem with your boat but don’t know which part is causing it? Review our complete troubleshooting table to find the right part to order from Diesel Pro Power.

Diesel Pro Power Is the Only Name You Need to Know for Allison Marine MH Parts

If you have been struggling to find quality Allison Marine MH parts, you’re in luck. You have not only found a reliable source for Allison Marine MH parts — you have found the best possible source. Why? Because we put customers first.

What does that mean? For one, it means an intuitive, easy-to-use website. We know that when you need a replacement part, you’re not in the mood to waste time searching for the right piece. We make it so you can log on, see a clear picture of the part you need, click on it and have it on the way to you fast.

We mean fast, too. We’re proud of our ability to ship within 24 hours worldwide. And just because you get your part fast doesn’t mean there’s any decline in quality. Each premium part we send comes with a full warranty on defects in materials and workmanship under normal use and service. You also get our 100 percent quality guarantee that the part you receive will meet or exceed OEM specifications.

Take a look on our website and find the Allison Marine MH part you need and order it today. If you have any questions, concerns or comments, call us! We love to get feedback and talk parts with our customers.

Marine Transmission Specifications & Applications of the Allison MH Series

Overview of the Allison MH Series Marine Transmission

The Allison MH Series marine transmissions are hydraulically actuated gearboxes developed for use with Detroit Diesel two-stroke engines. Designed for medium- to heavy-duty commercial marine applications, these transmissions offered smoother gear engagement, higher torque capacity, and lower maintenance cycles than their mechanically shifted M Series counterparts.

Produced under the Allison Division of General Motors and later Detroit Diesel, the MH Series was widely installed in government, commercial, and industrial vessels throughout the 1970s to 1990s. These transmissions remain operational in legacy fleets due to their dependable service life, compatibility with Detroit engines, and robust rebuildability.

Key Specifications of the Allison MH Series

• Transmission Type: Hydraulically shifted marine gear

• Control System: Hydraulic shift with mechanical or solenoid control valves

• Typical Models: MH20, MH25, MH30, MH40, MH45

• Input Power Range:

• MH20: up to ~300 HP

• MH25: up to ~400 HP

• MH30: up to ~500 HP

• MH40: up to ~650 HP

• MH45: up to ~800 HP

• Reduction Ratios Available (varies by model):

• 1.00:1

• 1.48:1

• 2.00:1

• 2.48:1

• 3.00:1

• Input Housing: SAE No. 1, No. 2, or No. 3 (depending on configuration)

• Output Shaft: Straight or down-angle, flange-mounted

• Clutch Type: Oil-cooled multi-disc hydraulic clutch

• Cooling System: Oil-to-water heat exchanger standard

• Lubrication: Pressurized internal lubrication system

• Weight: Approximately 600–900 lbs (model-dependent)

The Allison MH Series offers durable hydraulic shifting that delivers reliable performance under continuous load, ideal for pushboats, twin-screw vessels, and boats requiring frequent gear reversals.

OEM Detroit Diesel Engine Pairings with Allison MH Series

The Allison MH Series was purpose-built for seamless integration with Detroit Diesel Series 53, 71, and 92 engines, across a wide range of 2-stroke configurations.

Detroit Diesel Series 53

• 6-53: Paired with MH20 or MH25 (utility and light-duty patrol vessels)

Detroit Diesel Series 71

• 6-71: Paired with MH20 or MH25

• 6V71: Paired with MH30 (common in ferries and twin-screw workboats)

• 8V71: Paired with MH30 or MH40 (used in tugs, ferries, and pilot vessels)

• 12V71: Paired with MH40 or MH45 (heavier vessels with dual-output requirements)

Detroit Diesel Series 92

• 6V92: Paired with MH30 or MH40 (popular in higher HP vessels)

• 8V92: Paired with MH40 or MH45 (used in powerful push boats and offshore service vessels)

• 12V92 / 16V92: Paired with MH45 (for high-horsepower towing and ocean-going workboats)

These pairings offered torque-matched performance, supported by SAE housing alignment and consistent shift quality under variable loads.

Common Marine Applications of Allison MH Series Transmissions

Thanks to their high torque rating and smooth shifting capabilities, the MH Series transmissions found success across a wide range of vessel types that demanded reliability and power:

• Tugboats and Push Boats: MH40 and MH45 were widely used with Detroit 8V92 and 12V71 engines

• Commercial Ferries: Offering seamless shifting in high-traffic routes

• Patrol and Enforcement Boats: Used by coast guards and harbor police vessels

• Pilot Boats: Twin-screw configurations with MH30 and 6V71 or 8V71 power

• Crew Transfer Vessels: Where continuous forward/reverse operation required hydraulic clutching

• Utility and Construction Barges: MH40 and MH45 paired with high-torque Detroit 2-strokes

Advantages of the Allison MH Series

• Hydraulic Shifting: Smooth and efficient under load, ideal for high-duty-cycle operations

• Durable Clutch System: Oil-cooled multi-disc clutches for longevity

• Designed for Detroit Diesel Engines: Seamless integration with factory engine specifications

• Supportable Long-Term: Components remain available for rebuild and maintenance

• Versatile Output Options: Straight and down-angle configurations suit varied hull types

• Robust Construction: Operates under saltwater, debris, and high-vibration environments

Ideal Use Cases for Allison MH Series Transmissions