2015 Ram 2500 Transmission & Axle Gear Ratios

Transmission gear ratios

The 2015 Ram 2500 was available with several transmission options, each carefully matched to the available engine choices to provide a balance of towing capability, payload capacity, and fuel economy. Below are the internal gear ratios for each transmission.

68RFE 6-Speed Automatic Transmission (6.7L Cummins Diesel)

AS69RC 6-Speed Automatic Transmission (6.7L Cummins Diesel - Aisin)

66RFE 6-Speed Automatic Transmission (5.7L HEMI V8 & 6.4L HEMI V8)

Available axle ratios

Ram offered a range of axle ratios for the 2015 Ram 2500, allowing buyers to configure their truck for specific needs, whether it be heavy-duty towing or improved fuel efficiency. The availability often depended on the engine choice and trim level.

How to identify your axle ratio

Identifying your Ram 2500's axle ratio is crucial for proper maintenance, parts replacement, and understanding your truck's capabilities. There are a few reliable methods to determine this information.

Door-jamb RPO sticker (FCA/Ram)

Ram (FCA) vehicles typically have a sticker on the driver's side door jamb, or occasionally in the glove box, that lists various option codes (RPOs - Regular Production Options). Look for a three-digit code starting with "DM" followed by a letter. For example:

• DMK: Indicates a 3.42 axle ratio
• DME: Indicates a 3.73 axle ratio
• DMH: Indicates a 4.10 axle ratio

If you cannot locate the RPO code, a Ram dealership can often provide a build sheet for your VIN, which will detail all factory options, including the axle ratio.

Axle Tag

While not always present or legible, some Ram axles may have a metal tag attached to one of the differential cover bolts. This tag often contains the gear ratio stamped directly on it. For example, "3.73" or "4.10." Clean the tag thoroughly to ensure accurate reading.

VIN Decoder

Online VIN decoder tools can sometimes provide information on your vehicle's original specifications, including the axle ratio. Be aware that the accuracy of third-party decoders can vary, so it's always best to cross-reference with other methods if possible.

Towing vs MPG impact

The axle ratio plays a significant role in the overall performance of your 2015 Ram 2500, particularly concerning towing capability and fuel economy.

• Numerically Lower Ratio (e.g., 3.42): A numerically lower axle ratio means the engine will operate at lower RPMs for a given road speed. This typically translates to better fuel economy during unladen highway driving. However, it will also result in reduced towing capacity and slower acceleration, as the engine has less mechanical advantage to get the load moving.

• Numerically Higher Ratio (e.g., 4.10): Conversely, a numerically higher axle ratio means the engine will operate at higher RPMs for a given road speed. This provides increased torque to the wheels, significantly improving towing capability, acceleration, and performance in challenging conditions. The trade-off is generally lower fuel economy, especially at highway speeds.

• Balanced Ratio (e.g., 3.73): A middle-ground ratio like 3.73 aims to strike a balance between decent fuel economy for daily driving and sufficient power for moderate towing.

When choosing or evaluating an axle ratio, consider your primary use for the truck. If heavy towing is a regular occurrence, a higher numerical ratio is beneficial. If the truck is mostly used for commuting or light-duty work, a lower numerical ratio will save you money at the pump.

Common issues

While the axles and differentials in Ram 2500 trucks are generally robust, some common issues can arise over time.

• Ring & Pinion Whine: A high-pitched whine that changes with vehicle speed and often load (accelerating vs. coasting) can indicate wear on the ring and pinion gears. This can be caused by improper setup (backlash and pattern), insufficient lubrication, or heavy use.

• Carrier Bearing Growl/Rumble: A rumbling or growling noise, particularly noticeable at certain speeds, may point to worn carrier bearings within the differential. These bearings support the differential carrier and can wear out due to age, mileage, or heavy loads.

• Limited-Slip Clutch Wear: If your Ram 2500 is equipped with a limited-slip differential, the clutch packs can wear out over time, leading to a loss of limited-slip function. Symptoms include one wheel spinning freely on slippery surfaces where both should be driving, or a chattering noise during tight turns (which can also be caused by incorrect fluid or friction modifier).

Regular differential fluid changes with the correct type of fluid (including friction modifier for limited-slip differentials) are critical for preventing premature wear and extending the life of these components.

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