2021 International LT: Transmission & Axle Gear Ratios

Transmission Gear Ratios

The 2021 International LT was offered with a variety of automated manual and manual transmissions from top manufacturers like Eaton and Cummins. Each is designed to maximize performance and fuel efficiency for specific applications.

Eaton Endurant 12-Speed Automated Manual

This is a popular option known for its smooth shifting and fuel economy.

Eaton Fuller RTLO-16913A 13-Speed Manual

A versatile manual option for drivers who prefer more control, especially in varied terrain.

Eaton Fuller RTLO-18918B 18-Speed Manual

The top choice for heavy-haul applications, providing maximum gear splits for ultimate control under heavy loads.

Available Axle Ratios

Axle ratios are a critical component in spec'ing a truck for its intended purpose. International trucks are typically ordered to spec, so there isn't a specific "trim" they come with. Instead, the ratio is chosen based on the engine, transmission, and intended application (e.g., long-haul, regional, heavy-haul).

How to Identify Your Axle Ratio

Unlike consumer trucks, most Class 8 trucks like the International LT do not have a simple RPO code sticker in the door jamb for driveline components. Identification is usually done in one of two ways:

1. Axle Tag: The most reliable method is to locate the metal tag on the differential housing itself. The tag is typically bolted to the housing and will have the manufacturer (e.g., Meritor, Dana) and the specific ratio (e.g., "3.36") stamped directly onto it.
2. VIN Decoder / Build Sheet: The original build sheet or a comprehensive VIN decoding service can provide the exact specifications the truck was built with from the factory, including the drive axle model and gear ratio.

Towing vs. MPG Impact

The relationship between axle ratios and performance is a trade-off between pulling power and fuel efficiency.

• Numerically Lower Ratios (e.g., 2.26, 2.47): These are known as "fast" ratios. The driveshaft turns fewer times for each rotation of the wheels. This results in lower engine RPM at highway speeds, which significantly improves fuel economy. These ratios are ideal for long-haul carriers traveling on relatively flat terrain where the truck can stay in top gear for extended periods.

• Numerically Higher Ratios (e.g., 3.36, 3.55): These are "slow" ratios. The driveshaft turns more times for each wheel rotation, multiplying the engine's torque. This provides superior pulling power, making it easier to get heavy loads moving and to maintain speed on steep grades. These ratios are best for heavy-haul, regional, or vocational applications where loads are heavier and terrain is more varied.

Common Issues

The drive axles used in the International LT are built by reputable manufacturers like Meritor and Dana and are generally robust. However, like any heavy-duty component, they can experience wear over hundreds of thousands of miles.

• Pinion and Ring Gear Whine: A howling or whining noise from the rear axle that changes pitch with vehicle speed can indicate worn pinion and ring gears. This is often caused by high mileage or improper lubrication.
• Carrier Bearing Failure: A rumbling or grinding noise, especially on acceleration or deceleration, can point to failing carrier bearings. If left unaddressed, this can lead to catastrophic axle failure.
• Axle Seal Leaks: Leaks at the pinion seal (where the driveshaft enters the differential) or at the axle shafts are common maintenance items. It's crucial to address them promptly to avoid loss of lubrication and subsequent gear damage.

If you're experiencing driveline issues or need help identifying your components, find a qualified heavy-duty driveline shop on Repairius.