2021 Ram 2500 Transmission & Axle Gear Ratios

When it comes to heavy-duty trucks, the powertrain configuration dictates exactly how the vehicle performs under stress, load, and long highway drives. The 2021 Ram 2500 is a powerhouse available with two distinct engines: the 6.4L HEMI V8 and the legendary 6.7L Cummins Turbo Diesel. Connecting this power to the pavement is a combination of sophisticated transmissions and heavy-duty solid axles.

Understanding your gear ratios is critical if you plan on towing heavy fifth-wheel trailers, upgrading to larger off-road tires, or simply trying to maximize your fuel economy on long highway hauls. Below is the ultimate reference guide for the 2021 Ram 2500 transmission internal gears and differential axle ratios.

Transmission gear ratios

The 2021 Ram 2500 utilizes two primary transmissions depending on the engine selection. The 6.4L HEMI V8 is mated to the TorqueFlite 8HP75-LCV 8-speed automatic, which provides excellent step-gear spacing for smooth acceleration. The 6.7L Cummins Standard Output diesel uses the proven 68RFE 6-speed automatic transmission, designed specifically to handle the massive low-end torque of the inline-six diesel.

TorqueFlite 8HP75-LCV 8-Speed Automatic (6.4L HEMI V8)

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

Available axle ratios

Ram keeps the 2500 axle ratio options relatively streamlined compared to the half-ton market, relying on the massive torque output of the engines and deep transmission gearing to do the heavy lifting. The Ram 2500 utilizes heavy-duty American Axle & Manufacturing (AAM) axles front and rear.

Note: The 6.7L Cummins in the 2500 is exclusively paired with the 3.73 ratio for the 2021 model year. The 4.10 ratio is restricted to the gas-powered 6.4L HEMI to help it stay in its higher powerband while towing.

How to identify your axle ratio

If you are buying a used 2021 Ram 2500 or just want to confirm what is underneath your truck, there are a few surefire ways to check your differential ratio:

1. The Axle Tag: The most reliable method is to crawl under the rear of the truck and look at the differential cover. Factory AAM axles typically have a metal tag bolted to one of the differential cover bolts, or a white sticker on the axle tube. This tag will have the ratio stamped directly on it (e.g., "3.73" or "4.10").
2. Door-Jamb RPO Sticker / Monroney Label: While GM relies heavily on the glovebox RPO sticker, Ram vehicles often list their specific powertrain details on the original window sticker. You may also find an equipment identification sticker in the glovebox or driver's side door jamb with a three-letter sales code (DME for 3.73, DMF for 4.10).
3. VIN Decoder: Because heavy-duty trucks have specific tow ratings based on their axles, running your 17-digit Vehicle Identification Number (VIN) through a mopar VIN decoder or contacting a Ram dealer parts department will instantly tell you the factory-installed gear ratio.

Towing vs MPG impact

Your axle ratio acts as a mechanical torque multiplier. The choice between a 3.73 and a 4.10 ratio significantly alters how your Ram 2500 behaves on the road.

Numerically Lower Ratio (3.73): Often called a "taller" gear, the 3.73 allows the driveshaft to spin fewer times for every rotation of the tires. This keeps engine RPMs lower at highway speeds, resulting in better fuel economy (MPG) and a quieter cabin. For the high-torque Cummins diesel, a 3.73 is more than enough to max out the chassis' towing capacity without needing deeper gears.

Numerically Higher Ratio (4.10): Known as a "shorter" or "deeper" gear, the 4.10 forces the engine to rev slightly higher at a given speed. This is incredibly beneficial for the 6.4L HEMI V8 when towing heavy loads, as it gets the engine into its peak horsepower and torque band faster. The trade-off is lower highway fuel economy, but it offers far better off-the-line acceleration and less transmission gear-hunting on steep grades.

Common issues

The AAM 11.5-inch rear axle used in the Ram 2500 is famously robust, but like all mechanical components, it can experience issues, particularly if subjected to severe duty without proper maintenance.

• Ring & Pinion Whine: Sometimes reported after heavy towing during the break-in period if the differential fluid wasn't changed properly. A faint deceleration whine can occasionally develop due to gear backlash falling out of tolerance.
• Limited-Slip Clutch Wear: For trucks equipped with the Anti-Spin rear differential, the clutch packs can wear out over time, especially if subjected to frequent off-road use or tight cornering under load. If you experience "chatter" around corners, it may be time for a fluid change and fresh friction modifier, or a clutch pack rebuild.
• Carrier Bearing Vibrations: While technically a driveshaft issue rather than an internal axle issue, multi-piece driveshafts on long-bed or Mega Cab configurations can experience center support (carrier) bearing wear, leading to a noticeable driveline shudder upon takeoff.

Whether you need a simple fluid service, a ring and pinion swap for larger tires, or a complete differential rebuild, professional help is essential for setting proper gear backlash and preload.

Find a driveline shop on Repairius.