2022 Kenworth T680 Transmission & Axle Gear Ratios

Transmission Gear Ratios

The 2022 Kenworth T680, a popular choice for long-haul and regional trucking, offers a variety of transmission options from Eaton, a leader in heavy-duty transmissions. These transmissions are designed to optimize performance, fuel efficiency, and drivability across diverse applications. The internal gear ratios play a crucial role in how the engine's power is delivered to the drive wheels, impacting everything from starting torque to highway cruising speed.

Here are some of the common Eaton transmissions found in the 2022 Kenworth T680, along with their typical gear ratios. Please note that specific ratios can vary slightly depending on the exact transmission model and build configuration.

Eaton Fuller Advantage 10-Speed Automated Manual Transmission (AMT)

This popular AMT is known for its fuel efficiency and driver comfort, as it eliminates the need for manual shifting.

Gear	Ratio
1st	14.40
2nd	9.00
3rd	6.57
4th	5.09
5th	3.90
6th	2.94
7th	2.29
8th	1.76
9th	1.35
10th	1.00
Reverse	14.93

Eaton Fuller Advantage 12-Speed Automated Manual Transmission (AMT)

Offering more gears for finer control and potentially better fuel economy in certain applications.

Gear	Ratio
1st	16.29
2nd	13.01
3rd	10.33
4th	8.24
5th	6.54
6th	5.23
7th	4.16
8th	3.32
9th	2.64
10th	2.11
11th	1.67
12th	1.27
Reverse	16.73

Eaton Fuller 13-Speed Manual Transmission

A classic choice for drivers who prefer a manual transmission, offering versatility for different hauling needs.

Gear	Ratio
1st	18.00
2nd	12.87
3rd	9.22
4th	6.63
5th	4.75
6th	3.63
7th	2.76
8th	2.00
9th	1.43
10th	1.00
11th	0.86
12th	0.73
13th (Overdrive)	0.60
Reverse	18.73

Available Axle Ratios

The rear axle ratio is another critical component in the powertrain, working in conjunction with the transmission to determine the overall gear reduction. A higher (numerically larger) axle ratio provides more torque multiplication at the wheels, making it better for heavy hauling and stop-and-go conditions. Conversely, a lower (numerically smaller) axle ratio results in lower engine RPMs at highway speeds, improving fuel economy.

The 2022 Kenworth T680 offers a range of axle ratios to cater to diverse operational requirements. Specific availability often depends on the chosen engine, transmission, and application package.

Ratio	Available With (Engine/Trim/Package)	RPO/Axle Code	Best For
2.47	PACCAR MX-13 / Cummins X15 (Efficiency Series), Aerodynamic Packages	Varies by manufacturer	Excellent Fuel Economy (Long-haul, flat terrain)
2.64	PACCAR MX-13 / Cummins X15 (Efficiency Series), Balanced Packages	Varies by manufacturer	Improved Fuel Economy, Light to Moderate Hauling
2.79	PACCAR MX-13 / Cummins X15, Versatile Hauling Packages	Varies by manufacturer	Balanced (Fuel Economy & Moderate Towing)
2.93	Cummins X15 Performance Series, Heavy-Duty Hauling Packages	Varies by manufacturer	Moderate Towing, Hilly Terrain
3.08	Cummins X15 Performance Series, Severe-Duty Hauling Packages	Varies by manufacturer	Heavy Towing, Vocational Use
3.25	Specialized Heavy Haul	Varies by manufacturer	Max Towing, Low Speed Maneuvering

Note: "Varies by manufacturer" for RPO/Axle Code is used here as Kenworth typically sources axles from Dana or Meritor, and their coding systems differ. Always refer to your specific truck's documentation.

How to Identify Your Axle Ratio

Identifying your axle ratio is crucial for proper maintenance, parts ordering, and understanding your truck's performance characteristics. Here are the most common methods for the Kenworth T680:

1. Axle Tag (Most Reliable)

Dana and Meritor, the primary suppliers of axles for Kenworth, will typically have a metal tag bolted to one of the differential cover bolts or on the axle tube itself. This tag contains vital information, including the axle model number, serial number, and most importantly, the gear ratio. The ratio will usually be stamped directly (e.g., "3.55") or indicated by a numerical code that can be cross-referenced.

2. Build Sheet / Line Set Ticket

When your Kenworth T680 was manufactured, it came with a detailed build sheet or "line set ticket." This document lists all the major components and their specifications, including the exact axle ratio. This is often found in the glove compartment or with the truck's original paperwork.

3. Dealer or Manufacturer Reference

If you have the Vehicle Identification Number (VIN) of your truck, a Kenworth dealer or a heavy-duty truck service center with access to Kenworth's database can look up the original specifications, including the axle ratio.

4. Technician Inspection (Last Resort)

In some cases, if no other information is available, a qualified technician can remove the differential cover and count the teeth on the ring and pinion gears. The axle ratio is determined by dividing the number of teeth on the ring gear by the number of teeth on the pinion gear (e.g., 41 ring gear teeth / 11 pinion gear teeth = 3.73 ratio).

Towing vs MPG Impact

The choice of axle ratio has a direct and significant impact on your truck's towing capability and fuel economy:

• Numerically Lower Ratio (e.g., 2.47, 2.64): Better MPG, Lower Towing Capacity. A lower numerical ratio means fewer engine revolutions per tire rotation. This results in the engine operating at lower RPMs at highway speeds, which generally translates to better fuel efficiency. However, it also means less torque multiplication at the drive wheels, making it less suitable for heavy loads, steep grades, or frequent stop-and-go driving. Trucks configured for long-haul, light-load, or aerodynamic applications often utilize these ratios.

• Numerically Higher Ratio (e.g., 2.93, 3.08, 3.25): Greater Towing Capacity, Lower MPG. A higher numerical ratio means more engine revolutions per tire rotation. This provides significantly more torque multiplication, allowing the truck to pull heavier loads, climb hills more easily, and accelerate faster, especially from a standstill. The trade-off is that the engine will operate at higher RPMs at highway speeds, consuming more fuel. These ratios are preferred for heavy hauling, vocational applications, or operating in mountainous terrain.

Selecting the correct axle ratio is a crucial decision that should align with the primary application and expected operating conditions of the truck to achieve the optimal balance between performance and fuel efficiency.

Common Issues

While Kenworth T680 drivetrains are generally robust, like any mechanical system subject to heavy loads and continuous operation, certain issues can arise:

• Ring & Pinion Whine: A howling or whining noise that changes with road speed and typically occurs during acceleration or deceleration can indicate wear or improper mesh between the ring and pinion gears. This often necessitates replacement of the gear set and proper setup.

• Carrier Bearing Wear: The bearings supporting the differential carrier can wear out, leading to growling noises, especially when turning, or excessive play in the driveline. This requires replacing the worn bearings.

• Limited-Slip Clutch Wear (if equipped): If your T680 is equipped with a limited-slip differential, the internal clutch packs can wear over time, leading to a loss of traction in slippery conditions or chattering/binding during turns. This typically requires rebuilding the limited-slip unit.

Regular maintenance, including proper lubrication and timely fluid changes, is essential to prolong the life of your transmission and axle components.

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