2020 Kenworth W900 – Transmission & Axle Gear Ratios

Transmission gear ratios

The 2020 Kenworth W900, a legendary workhorse, offered a variety of transmission options to suit diverse hauling needs. While specific internal gear ratios can vary slightly based on the exact transmission model and its configuration, here's a general overview of common options. The most popular transmissions for the W900 included various Eaton Fuller Roadranger manual and automated manual transmissions (AMTs).

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

Eaton Fuller FO-16E318B-VXP (18-Speed Automated Manual)

Available axle ratios

The choice of axle ratio significantly impacts the 2020 Kenworth W900's performance, dictating the balance between fuel economy and pulling power. Kenworth offered a wide range of ratios to optimize the truck for various applications, from long-haul highway cruising to heavy-haul operations.

Note: Specific RPO/Axle Codes vary by manufacturer and can often be found on a build sheet or an informational sticker on the vehicle. For Kenworth, these codes are typically found on the driver's door jamb sticker or a data plate within the cab. You may also find it stamped on the axle housing itself.

How to identify your axle ratio

Identifying the axle ratio on your 2020 Kenworth W900 is crucial for maintenance, repairs, and understanding your truck's capabilities. Here are common methods:

• Door-Jamb Sticker: For Kenworth trucks, a label on the driver's side door jamb or inside the glove compartment often contains a wealth of vehicle information, including RPO (Regular Production Option) codes. These codes list all the equipment your truck was built with. Look for a code that indicates the axle ratio. It might be a three-digit code or a more descriptive alphanumeric combination.
• Axle Tag: Many heavy-duty axles have a metal tag bolted to one of the differential cover bolts or stamped directly on the axle housing. This tag will typically display the axle manufacturer, model, and the gear ratio.
• Build Sheet/VIN Decoder: If you have access to the truck's original build sheet, the axle ratio will be clearly listed. Alternatively, a Kenworth dealership or online VIN decoder service can often provide detailed specifications, including the axle ratio, using your truck's Vehicle Identification Number (VIN).

Towing vs MPG impact

The axle ratio in your Kenworth W900 plays a pivotal role in determining its performance characteristics:

• Numerically Lower Ratio (e.g., 2.64, 2.79): These are often referred to as "tall" gears. They allow the engine to operate at lower RPMs at highway speeds, leading to better fuel economy. However, with lower RPMs, there's less torque multiplication, meaning reduced pulling power. This configuration is ideal for long-haul operations with lighter loads or where fuel efficiency is the top priority.
• Numerically Higher Ratio (e.g., 3.42, 3.55, 3.70): These are considered "short" gears. They provide greater torque multiplication, allowing the truck to start heavier loads more easily and maintain speed on inclines. The tradeoff is that the engine will run at higher RPMs for a given road speed, consuming more fuel. These ratios are preferred for heavy-haul, vocational, or off-road applications where maximum pulling power and gradeability are essential.

Choosing the right axle ratio is a delicate balancing act that depends on the primary use case of the truck. A balanced ratio (e.g., 3.08 or 3.25) often provides a good compromise for mixed operations.

Common issues

While Kenworth W900 drivetrains are built for durability, certain issues can arise with prolonged use or improper maintenance:

• Ring & Pinion Whine: A common symptom of worn or improperly set up differential gears. This often manifests as a howling or whining noise that changes with road speed and load. It can indicate worn gear teeth, incorrect backlash, or bearing issues.
• Carrier Bearing Wear: The carrier bearings support the differential carrier within the axle housing. Wear here can lead to excessive play, noise, and eventually damage to the ring and pinion gears. Symptoms include clunking noises, vibrations, or a growling sound.
• Limited-Slip Clutch Wear (if equipped): If your W900 is equipped with a limited-slip differential, the clutch packs within it can wear out over time. This can result in a loss of traction in low-traction situations, chattering noises during turns, or a feeling of binding in the rear end.

Regular differential fluid changes and inspections are crucial for extending the life of your axle components and catching potential issues early.

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