2018 Ram 2500 Transmission & Axle Gear Ratios

Transmission gear ratios

The 2018 Ram 2500 offered two primary transmission options: the 68RFE 6-speed automatic for gasoline engines and the Aisin AS69RC 6-speed automatic for the high-output Cummins diesel.

68RFE Automatic Transmission (Gasoline)

Aisin AS69RC Automatic Transmission (Cummins Diesel)

| Gear | Ratio | | :------ | :----- |\n| 1st | 3.75 | | 2nd | 2.21 | | 3rd | 1.54 | | 4th | 1.00 | | 5th | 0.77 | | 6th | 0.63 | | Reverse | 3.51 |

Available axle ratios

The 2018 Ram 2500 offered several axle ratio options, allowing owners to optimize their trucks for various tasks, from heavy towing to improved fuel economy.

How to identify your axle ratio

Identifying your Ram 2500's axle ratio is crucial for proper maintenance, upgrades, and ensuring you have the right setup for your needs. Unlike some manufacturers, Ram (and the broader FCA/Stellantis group) often uses an RPO (Regular Production Option) code sticker to indicate axle ratios.

Door-Jamb RPO Sticker: Open the driver's side door and look for a sticker on the door jamb or the edge of the door itself. This sticker lists numerous three-digit codes. Look for a code beginning with "D," such as DMB (3.42), DME (3.73), or DMF (4.10). These codes directly correspond to your truck's final drive ratio.

Axle Tag: Older trucks or some aftermarket axles might have a metal tag attached to one of the differential cover bolts. This tag will often have the gear ratio stamped directly on it (e.g., "3.73"). However, with newer Ram trucks, the RPO sticker is the more common and reliable method.

VIN Decoder: Many online VIN decoder tools can provide a detailed build sheet for your vehicle, which will include the axle ratio. This is a good option if your RPO sticker is unreadable or missing.

Contact a Ram Dealership: With your VIN, a Ram dealership's parts or service department can provide you with the original build sheet for your truck, which will list all factory options, including the axle ratio.

Towing vs MPG impact

The choice of axle ratio significantly impacts your truck's performance characteristics, particularly concerning towing capability and fuel economy.

Numerically Lower Ratio (e.g., 3.42):

• MPG: Generally results in better fuel economy on the highway. With a lower ratio, the engine operates at lower RPMs at a given road speed, reducing fuel consumption.
• Towing: Provides less mechanical advantage, meaning the engine has to work harder to move heavy loads. This can lead to increased transmission temperatures and reduced towing capacity or more strain on the drivetrain. It's best suited for lighter towing tasks or primarily unladen highway driving.

Numerically Higher Ratio (e.g., 4.10):

• Towing: Offers greater mechanical advantage, allowing the engine to turn the wheels with less effort. This results in significantly improved towing capability, especially for heavy loads, steep grades, and frequent starts and stops. It also helps with maintaining speed when towing.
• MPG: Typically leads to lower fuel economy, especially at highway speeds. The engine will run at higher RPMs to maintain the same road speed, burning more fuel. Trucks with higher ratios are optimized for work and heavy hauling rather than maximum fuel efficiency.

Balanced Ratio (e.g., 3.73):

• Many owners find ratios like 3.73 to be a good compromise, offering a respectable balance between towing performance and fuel efficiency for a variety of uses.

When choosing or assessing your axle ratio, consider your primary use case. If you frequently tow heavy trailers, a higher numerically ratio is almost always the better choice. If your truck is mainly a daily driver with occasional light hauling, a lower ratio might be more appropriate.

Common issues

While the components are generally robust, like any mechanical system, the differentials and transmissions in a 2018 Ram 2500 can experience some common issues.

Ring & Pinion Whine: A persistent howling or whining noise that changes with vehicle speed (and sometimes load) can indicate wear or improper setup of the ring and pinion gears within the differential. This often becomes more noticeable between 40-70 mph and can be a sign of worn gear teeth, incorrect backlash, or bearing issues.

Carrier Bearing Wear: The bearings supporting the differential carrier can wear out over time, leading to noises (humming, rumbling) and, if severe, vibration. This wear can be accelerated by heavy towing or lack of proper differential fluid maintenance.

Limited-Slip Clutch Wear (where applicable): For trucks equipped with a limited-slip differential, the internal clutch packs can wear out. Symptoms include a chattering or binding sensation (especially when turning at low speeds), and a reduced ability for the limited-slip feature to transfer power to the wheel with traction.

Transmission Shifting Issues: While specific to the transmission rather than the axle, issues like harsh shifts, delayed engagement, or slipping can arise. For the 68RFE, some owners report solenoid block issues or converter clutch shudder. The Aisin AS69RC is generally known for its robustness but can still experience electronic control issues or wear over very high mileage.

Regular maintenance, including fluid changes for both the transmission and differentials, is key to preventing many of these issues and extending the life of your driveline components.

Find a driveline shop on Repairius.