Parts for Allison M Marine Transmission

If you have a boat that uses Allison Marine M gears and has parts that need replacing, you may fear all is lost. Where are you going to find Allison Marine M parts for sale these days? The answer, of course, is Diesel Pro Power. We sell a complete selection of Allison Marine M parts online, so we can have your engine running in virtually no time at all.

We can provide you with everything from rebuilt Allison M gears and clutch plates to hydraulic pumps and seals, washers and more. We can send you a complete overhaul kit, too, as well as selector valves, sleeves, springs, bolts or transmission bearings. We’ve also got gauges, couplings, oil filters and more. We even have marine controls, steering, cables, lights and manuals!

Having trouble locating the part you need? No problem. Just contact us and tell us what you’re looking for. We’ll find it for you or find you a similar part that does what you need just as well or better.

What if you don’t know what you need? We’ve got you covered there, too. Check out our convenient troubleshooting guide. Just find the parts that correspond in the grid to the problem you are having.

Diesel Pro Power Is Your Reliable Source for Allison Marine M Parts

There’s no need to search around for any other Allison Marine M Parts vendors when you have Diesel Pro Power right here. Our Allison Marine M Parts need to meet our high standards of quality so you know you’re getting a part you can rely on. We’ve made our website extremely easy to use because we understand how stressful trying to find replacement parts can be.

Over 15,000 happy customers will tell you that Diesel Pro Power is a great place to buy your replacement parts. We ship within 24 hours, so you won’t have to wait for a part you badly need. You’ll also appreciate the peace of mind that comes with our 100 percent quality guarantee. Each part we send to you will meet or exceed OEM specifications. We back that up with a full warranty on defects in materials and workmanship under normal use and service.

While we love to talk to our customers, we’re not here to waste your time. We’re here to make sure you get the right Allison Marine M parts as quickly as possible. That’s why we make ordering through the website so simple and why we ship in 24 hours all over the world. It’s also why we have friendly and knowledgeable staff available to help you with any questions or concerns you may have.

Your Allison Marine M part replacement worries are over. Diesel Pro Power is here whenever you need us.

Get that critical Allison Marine M part right now! Click on what you need and order it today!

Marine Transmission Specifications & Applications of the Allison M Series

Overview of the Allison M Series Marine Transmission

The Allison M Series marine transmissions are mechanically shifted gearboxes developed by the Allison Division of General Motors for use in marine propulsion systems. Built to match the performance profiles of Detroit Diesel 2-stroke engines, these transmissions were widely adopted from the 1950s through the 1980s for small to mid-sized commercial vessels, offering dependable performance with a straightforward, serviceable design.

Mechanical actuation and robust construction made the M Series ideal for fishing boats, harbor craft, and workboats operating in rugged, low-maintenance environments. These transmissions remain in active use in legacy fleets, especially in North America, Latin America, and the Caribbean.

Key Specifications of the Allison M Series

• Transmission Type: Mechanically actuated marine gear

• Shift Method: Manual lever or cable actuation

• Typical Models: M15, M20, M25, M30, M40

• Input Power Range:

  • M15: up to ~180 HP

  • M20: up to ~250 HP

  • M25: up to ~300 HP

  • M30: up to ~350 HP

  • M40: up to ~400 HP

• Reduction Ratios Available (varies by model):

  • 1.00:1 (direct drive)

  • 1.50:1

  • 2.00:1

  • 2.48:1

• Input Housing: SAE No. 2 or SAE No. 3

• Output Shaft: Straight output; flange-mounted

• Clutch Type: Dry or wet clutch (depending on model), manually engaged

• Lubrication: Splash or basic pump-fed system

• Cooling System: Optional external oil cooler

• Weight: 400–600 lbs (depending on model and configuration)

The Allison M Series was favored for its simplicity and rugged reliability—key attributes for vessels where electronic or hydraulic control systems were impractical.

OEM Detroit Diesel Engine Pairings with Allison M Series

The Allison M Series was engineered specifically for Detroit Diesel engines from the 53 and 71 Series. These pairings were standard in a wide range of commercial vessels during the second half of the 20th century.

Detroit Diesel Series 53

• 4-53: Paired with Allison M15 or M20

• 6-53: Paired with Allison M20 or M25
  These combinations were commonly found in harbor tugs, pilot boats, and small fishing vessels.

Detroit Diesel Series 71

• 4-71: Paired with Allison M20 (light-duty commercial applications)

• 6-71: Paired with Allison M25 or M30 (heavier fishing boats and utility vessels)

• 6V71: Paired with Allison M30 or M40 (used in twin-screw setups for mid-sized workboats)

• 8V71: Occasionally used with M40 in lower-load applications, though MH series was more typical at this HP level.

These OEM pairings were based on matching SAE housings, torque output, and duty cycle compatibility. M Series gearboxes were designed to handle the 180–400 HP range typical of these 2-stroke Detroit engines.

Common Marine Applications of Allison M Series Transmissions

Because of their manual operation and straightforward design, Allison M Series transmissions were widely used in applications where ease of repair and reliability were essential. Common marine uses included:

• Commercial Fishing Boats: Small trawlers, gillnetters, and lobster boats powered by 4-53 or 6-71 engines

• Harbor Patrol and Utility Boats: Municipal and industrial vessels where maintenance simplicity was a top priority

• Crew Boats and Launch Vessels: Operating short runs in nearshore environments

• Pilot Boats: Compact hulls with twin 6-71 engines and mechanical shift M30 or M40 transmissions

• Dredge Tenders and Inland Barges: Where slow-speed reliability and easy gear changes are critical

Advantages of the Allison M Series

• Proven Mechanical Reliability: Built for harsh marine environments and heavy-duty daily operation

• No Electronics or Hydraulics: Ideal for fleets in remote regions or with limited technical infrastructure

• Long-Term Serviceability: Parts availability and rebuild simplicity make them practical for aging vessels

• Factory-Matched to Detroit Diesel: Perfect integration with 53 and 71 Series engines

• Compact and Durable: Fits smaller engine rooms without compromising performance

Ideal Use Cases for Allison M Series Transmissions