2018 Freightliner M2 106 Transmission & Axle Gear Ratios

The 2018 Freightliner M2 106 is one of the most versatile and widely used medium-duty trucks on the road today. Whether it is configured as a box truck, a flatbed, a dump truck, or a dedicated tow rig, its performance is heavily dictated by its powertrain configuration. Specifically, the combination of its transmission gearing and rear axle ratio determines its startability, gradeability, and highway cruising efficiency.

Understanding the gear ratios in your 2018 Freightliner M2 106 is essential for fleet managers and owner-operators who want to maximize payload efficiency, fuel economy, or towing capability. Below is a comprehensive guide to the transmission and axle gear ratios available for this workhorse.

Transmission gear ratios

The 2018 Freightliner M2 106 was offered with a wide variety of transmissions, typically paired with the Cummins B6.7 or L9 engines. The most common selections for this chassis are the Allison RDS (Rugged Duty Series) and HS (Highway Series) automatics, along with Eaton Fuller manuals. Below are the internal gear ratios for the most popular automatic transmissions found in the M2 106.

Allison 2500 RDS / HS (6-Speed Automatic)

Commonly paired with the Cummins B6.7 for box trucks, beverage delivery, and light towing applications.

Allison 3000 RDS / HS (6-Speed Automatic)

Typically paired with the Cummins L9 or higher-output B6.7 engines for heavier applications like dump trucks, heavy towing, and utility vehicles.

Eaton Fuller FS-5406A (6-Speed Manual)

A staple manual transmission option for operators wanting direct control over their shift points.

Available axle ratios

The 2018 Freightliner M2 106 utilizes robust rear drive axles, most commonly sourced from Meritor or Dana Spicer. Because the M2 106 is highly customizable from the factory, axle ratios span a wide range to accommodate everything from high-speed highway delivery to low-speed, high-torque vocational work.

Note: Axle codes vary depending on the specific Gross Axle Weight Rating (GAWR) specified at the time of the build (e.g., 17,500 lbs, 21,000 lbs).

How to identify your axle ratio

Because medium-duty trucks are custom-spec’d, you cannot simply guess the axle ratio based on the engine. Here is how you can accurately identify the axle ratio on your 2018 Freightliner M2 106:

1. The Data Plate (Door Jamb Sticker): Check the driver’s side door jamb or the edge of the driver's door. Freightliner affixes a data plate here that lists the VIN, Gross Vehicle Weight Rating (GVWR), and specific component details. It often lists the front and rear axle models along with the specific rear axle ratio.
2. Axle Tag: Crawl under the rear of the truck (safely) and look at the differential housing. Meritor and Dana Spicer axles have a metal identification tag bolted to the differential cover or stamped into the housing. This tag will list the axle model, gear ratio (e.g., "4.88"), and the date of manufacture.
3. VIN Decoder or Dealership: If the tags are missing or illegible due to rust, you can run the 17-digit Vehicle Identification Number (VIN) through a commercial truck VIN decoder, or call a Freightliner dealership’s parts department. They can pull the original factory build sheet.

Towing vs MPG impact

The relationship between your rear axle ratio and vehicle performance is a critical balancing act:

• Numerically lower ratios (e.g., 3.90, 4.10): These are considered "tall" gears. They allow the driveline to spin slower at highway speeds, which keeps engine RPMs down. This results in significantly better fuel economy (MPG) and less engine noise during long highway runs. However, tall gears provide less mechanical torque multiplication, making it harder to get heavy loads moving from a dead stop.
• Numerically higher ratios (e.g., 5.29, 5.86): These are "short" gears. They provide maximum torque multiplication to the wheels. If you are towing heavy equipment, driving a dump truck, or operating in mountainous terrain, you need these ratios for startability and gradeability. The trade-off is reduced top speed and lower fuel economy, as the engine must run at higher RPMs on the highway.

Common issues

While the driveline components on the Freightliner M2 106 are built for severe duty, they are not immune to wear and tear. A few common issues to watch out for include:

• Ring and Pinion Whine: If the truck is heavily overloaded or driven with low gear oil, the ring and pinion gears can wear unevenly. This usually presents as a distinct whining or howling noise that changes pitch during acceleration or deceleration.
• Carrier Bearing Wear: The long driveshafts on M2 106 box trucks require carrier (center support) bearings. When these bearings wear out or the rubber insulator degrades, it causes a noticeable vibration under the cab, especially when taking off from a stop or at specific highway speeds.
• Pinion and Wheel Seal Leaks: High mileage and extreme thermal cycling can cause the seals on the Meritor or Dana axles to fail, leaking thick gear oil onto the brakes or the ground. Regularly checking differential fluid levels is crucial to prevent catastrophic gear failure.

Whether you need a simple gear oil change, a carrier bearing replacement, or a complete differential rebuild to change your axle ratio, having a qualified heavy-duty technician is paramount.

Find a driveline shop on Repairius.