2017 Kenworth T680 Transmission & Axle Gear Ratios

Transmission gear ratios

The 2017 Kenworth T680 was available with a variety of transmission options, primarily focusing on efficiency and performance for various hauling needs. The most common transmissions included Eaton Fuller automated manuals and a few manual options.

Eaton Fuller Advantage FRO-16210C (10-Speed Automated Manual)

Eaton Fuller UltraShift PLUS FO-16E310C-VXP (10-Speed Automated Manual)

Available axle ratios

The 2017 Kenworth T680 offered a range of axle ratios to optimize for fuel economy, versatility, or heavy-haul capabilities. The choice of axle ratio significantly impacts the truck's performance characteristics.

How to identify your axle ratio

For a Kenworth T680, identifying your axle ratio is crucial for proper maintenance and parts ordering. Unlike some other manufacturers, Kenworth does not typically use a "door-jamb RPO sticker" as seen on GM vehicles for axle codes. Instead, you'll usually find the axle information in a few key places:

• Build Sheet/Spec Sheet: The most accurate place to find your original axle ratio is on the build sheet or detailed specification sheet for your specific truck. This document was provided when the truck was purchased new.
• Axle Tag: Most heavy-duty axles will have a metal tag bolted to the axle housing itself. This tag contains vital information, including the axle model, serial number, and the gear ratio. You may need to clean off dirt and grease to read it clearly. It's often located on the front or rear of the axle housing, sometimes near the differential cover bolts.
• VIN Decoder: While not always providing the exact axle ratio directly, a comprehensive VIN decoder service can sometimes provide a build sheet or detailed equipment list that includes axle specifications.
• Contact Kenworth Dealer: If all else fails, a Kenworth dealer can typically look up your truck's specifications using the VIN.

Towing vs MPG impact

Understanding the relationship between axle ratio, towing capacity, and fuel economy is vital for maximizing the efficiency and performance of your 2017 Kenworth T680.

• Numerically Lower Ratio (e.g., 2.64, 2.79): These "taller" axle ratios result in lower engine RPMs at highway speeds. This translates directly to better fuel economy as the engine doesn't have to work as hard to maintain speed. However, they reduce the torque multiplication to the drive wheels, meaning the truck will have reduced towing capability and may struggle more when starting from a stop with a heavy load or on inclines.

• Numerically Higher Ratio (e.g., 3.42, 3.55): These "shorter" axle ratios provide greater torque multiplication to the drive wheels. This significantly enhances towing capability, making the truck more adept at pulling heavy loads, accelerating with a full trailer, and handling steep grades. The trade-off is decreased fuel economy, as the engine will be running at higher RPMs to maintain the same road speed.

Choosing the optimal axle ratio depends heavily on the primary application of the truck. Fleets focused on long-haul, light-load operations will prefer lower ratios, while those in vocational or heavy-haul sectors will opt for higher ratios.

Common issues

While Kenworth T680 axles are generally robust, some common issues can arise:

• Ring & Pinion Whine: A persistent whining noise that changes with road speed and load can indicate wear or improper setup of the ring and pinion gears. This often necessitates disassembly and replacement of the gears.
• Carrier Bearing Wear: The bearings supporting the differential carrier can wear over time, leading to humming or growling noises, particularly during acceleration or deceleration. If left unchecked, this can lead to more significant damage.
• Limited-Slip Clutch Wear: For trucks equipped with limited-slip differentials, the internal clutches can wear out, leading to a loss of traction in low-grip situations or clunking/chattering noises during turns.
• Axle Seal Leaks: Over time, axle seals can harden or become damaged, leading to leaks of differential fluid. This is important to address promptly to prevent fluid loss and potential internal damage.

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