2014 Kenworth T680 Transmission & Axle Gear Ratios

Transmission gear ratios

The 2014 Kenworth T680 was a highly versatile truck, available with a wide array of transmission options to suit diverse operational needs, from long-haul efficiency to heavy-haul capability. While specific internal gear ratios can vary slightly depending on the exact model and build, the most common configurations included manual transmissions from Eaton-Fuller and automated manual transmissions (AMTs) like the Eaton UltraShift PLUS.

Here are representative gear ratios for some popular transmission options:

Eaton Fuller RTLO-18918B (18-speed Manual)

Eaton UltraShift PLUS FO-16E318B-VXP (18-speed AMT)

Available axle ratios

The 2014 Kenworth T680 was offered with a wide range of axle ratios to optimize performance for various applications. These ratios were typically paired with specific engine configurations and intended uses.

Note: "Various" in the RPO/Axle Code column indicates that the specific code will depend on the axle manufacturer (e.g., Meritor, Dana) and the precise configuration. Always verify with your truck's documentation.

How to identify your axle ratio

Identifying your Kenworth T680's axle ratio is crucial for proper maintenance and understanding its performance characteristics. Unlike some light-duty trucks that use RPO stickers on door jambs, heavy-duty trucks like the T680 typically have the axle ratio information on an axle tag or within the vehicle's build sheet.

• Axle Tag: Look for a metal tag usually bolted to one of the axle housing bolts. This tag will often contain the axle manufacturer, model number, and the numerical ratio (e.g., "3.36"). It might be dirty or obscured, so cleaning may be necessary.
• VIN Decoder/Build Sheet: The most accurate way to determine your truck's exact specifications, including axle ratio, is through the vehicle's original build sheet or by running a VIN decoder through a Kenworth dealership or a specialized heavy-duty truck parts supplier. This will provide a comprehensive list of all installed components.
• Manual Calculation (Last Resort): If the above methods are not feasible, you can manually calculate the ratio. Jack up the drive wheels, mark a drive wheel and the driveshaft, and rotate the wheel exactly two full revolutions while counting the number of driveshaft rotations. The number of driveshaft rotations will approximate your axle ratio.

Towing vs MPG impact

The axle ratio has a profound impact on the performance and fuel efficiency of your 2014 Kenworth T680:

• Numerically Lower Ratio (e.g., 2.64, 2.79): A numerically lower ratio means the driveshaft rotates fewer times for each revolution of the wheel. This results in lower engine RPMs at highway speeds, leading to better fuel economy. However, it also means less torque multiplication at the wheels, making it less suitable for heavy loads or steep grades. These ratios are best for long-haul applications with light to moderate loads where maximizing MPG is the priority.

• Numerically Higher Ratio (e.g., 3.55, 3.70, 3.91): A numerically higher ratio means the driveshaft rotates more times for each revolution of the wheel. This results in higher engine RPMs for a given road speed, which provides greater torque multiplication to the wheels. This is ideal for heavy towing, vocational applications, and operating in hilly or mountainous terrain where maximum pulling power is needed. The trade-off is reduced fuel economy due to the engine working harder at higher RPMs.

Choosing the right axle ratio depends entirely on the primary application of the truck. A balanced ratio (e.g., 3.08, 3.25) offers a compromise between fuel efficiency and pulling power.

Common issues

While Kenworth T680 driveline components are generally built for durability, certain issues can arise over time related to the axles and differentials:

• Ring & Pinion Whine: A common symptom of worn or improperly set up ring and pinion gears is a distinct whine that changes pitch with vehicle speed and load. This can be caused by improper backlash, worn bearings, or insufficient lubrication. Ignoring a whine can lead to catastrophic failure.
• Carrier Bearing Failure: The carrier bearings support the differential carrier within the axle housing. Wear or failure of these bearings can manifest as a growling noise, especially when cornering, or excessive play in the driveshaft.
• Limited-Slip Clutch Wear (if equipped): Trucks equipped with limited-slip differentials may experience wear of the internal clutch packs. Symptoms include a noticeable clunk or binding sensation when turning slowly, or a reduced ability of the limited-slip feature to transfer power effectively to both wheels.
• Seal Leaks: Axle seals (pinion seal, axle shaft seals) can wear out over time, leading to leaks of differential fluid. This not only creates a mess but can also lead to fluid starvation and damage to internal components if not addressed.

Regular differential fluid changes with the correct type and viscosity of lubricant, along with proper inspection during routine maintenance, can significantly extend the life of these components and help identify potential issues before they become critical failures.

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