2015 Ram 3500: Transmission & Axle Gear Ratios

An in-depth look at the gear ratios, axle options, and driveline specifications for the 2015 Ram 3500 heavy-duty truck.

Transmission Gear Ratios

The 2015 Ram 3500 was available with three distinct six-speed transmission options, each designed to pair with specific engines and handle different workloads. The choice of transmission directly impacts the truck's driving characteristics, from pulling power to highway efficiency.

G56 (6-Speed Manual) Exclusively available with the 6.7L Cummins Turbo Diesel, the Mercedes-sourced G56 is a heavy-duty manual transmission favored by traditionalists. Its deep first gear provides excellent starting torque for heavy loads.

68RFE (6-Speed Automatic) This Chrysler-built automatic was the standard pairing for the 5.7L HEMI V8, 6.4L HEMI V8, and the standard-output 6.7L Cummins engine. It offers smooth shifting and a wide gear spread for a balance of acceleration and economy.

Aisin AS69RC (6-Speed Automatic) A heavy-duty commercial-grade automatic transmission from Aisin, this unit was mandatory for the high-output and max-tow Cummins engine packages. It's engineered for superior durability and heat management under the most demanding towing conditions.

Available Axle Ratios

The axle ratio is the final, critical link in the powertrain, multiplying torque one last time before it reaches the wheels. Selecting the right axle ratio is a balance between raw towing power and optimal fuel economy. The 2015 Ram 3500 used robust axles from American Axle & Manufacturing (AAM).

How to Identify Your Axle Ratio

Not sure which ratio your truck has? There are a few easy ways to find out.

1. Glove Box Sticker: Unlike GM, Ram doesn't typically put an RPO sticker on the door jamb. Instead, open your glove box and look for a white sticker titled "Vehicle Information." This sticker lists the "Sales Codes" for all options installed on your truck from the factory. Look for the codes listed in the table above (DMH, DMP, or DMM) to identify your ratio.

2. Axle Differential Tag: Look at the rear axle's differential (the large "pumpkin" in the middle). Bolted to the differential cover, you should find a small metal tag. This tag has several numbers stamped into it, but the important one will clearly indicate the ratio, such as "3 42" or "4 10". It may be partially obscured by dirt or rust, so you might need to clean it off.

3. VIN Decoder: You can use an online VIN decoder service to get a full build sheet for your truck. Entering your 17-digit Vehicle Identification Number will provide a detailed report, including the factory-installed axle ratio.

Towing vs. MPG Impact

Understanding the trade-offs between axle ratios is simple:

• Numerically Lower Ratio (e.g., 3.42): This is the "economy" gear. The engine needs to turn fewer RPMs to maintain a certain highway speed. This reduces fuel consumption and engine noise, making it ideal for trucks that spend most of their time cruising with light or no loads. The downside is less torque multiplication, which means the engine has to work harder to get a very heavy trailer moving.

• Numerically Higher Ratio (e.g., 4.10): This is the "power" gear. It multiplies engine torque more effectively, making it much easier to pull heavy loads from a stop and maintain speed on steep grades. It gives the truck a stronger, more responsive feel. The trade-off is that the engine spins at a higher RPM on the highway, leading to significantly increased fuel consumption.

• Balanced Ratio (3.73): This ratio is the jack-of-all-trades, offering a good compromise between the two extremes. It provides respectable towing capability without the major fuel economy penalty of the 4.10 ratio, making it a popular all-around choice.

Common Driveline Issues

While the AAM axles in the Ram 3500 are known for their strength, high mileage and heavy use can lead to a few common issues.

• Ring & Pinion Whine: A high-pitched whine that changes in pitch with vehicle speed (not engine RPM) is a classic symptom of a worn pinion bearing or an improper gear setup. The noise may be more noticeable during acceleration or deceleration.
• Carrier Bearing Failure: The carrier bearings support the differential case within the axle housing. If they begin to fail, they can produce a rumbling or grinding noise that also varies with vehicle speed.
• Limited-Slip Clutch Wear: On models equipped with a limited-slip differential (LSD), the internal clutch packs can wear out over time. This reduces the differential's ability to send power to both rear wheels on slippery surfaces, which you might notice as excessive one-wheel-peel.

If you're experiencing driveline noise, vibrations, or aren't sure which axle ratio is right for your needs, expert help is available. Find a driveline shop on Repairius.