2020 Chevrolet Silverado 3500HD Transmission & Axle Gear Ratios

In the demanding world of heavy-duty trucks, understanding the powertrain's gearing is paramount. For the 2020 Chevrolet Silverado 3500HD, the right combination of transmission and axle ratios can dramatically impact towing capability, fuel efficiency, and overall driving experience. This guide will break down the available options and provide insights to help you make informed decisions.

Transmission gear ratios

For 2020, the Silverado 3500HD offered two primary transmissions:

GM 6L90 (6-Speed Automatic)

GM Allison 10L1000 (10-Speed Automatic)

Available axle ratios

The 2020 Chevrolet Silverado 3500HD offered a range of axle ratios designed to suit various owner needs, from heavy-duty towing to more balanced performance.

How to identify your axle ratio

Identifying your Silverado 3500HD's axle ratio is crucial for understanding its capabilities and for ordering correct replacement parts. For General Motors vehicles like the Silverado, the most reliable method is to check the RPO (Regular Production Option) sticker.

This sticker is typically located on the glove box door or, less commonly, on the driver's side door jamb. Look for three-character codes. The axle ratio codes are usually GT4 for the 3.42:1 ratio and GT5 for the 3.73:1 ratio.

Alternatively, you can contact a Chevrolet dealership with your VIN, and they can provide a build sheet detailing all the options, including the axle ratio.

Towing vs MPG impact

The choice of axle ratio has a direct and significant impact on both towing performance and fuel economy:

• Numerically Higher Ratio (e.g., 3.73:1): This means the driveshaft makes more revolutions for every one revolution of the wheel. This provides greater torque multiplication, which is excellent for towing heavy loads, particularly from a standstill or on inclines. However, at highway speeds, the engine will run at higher RPMs, leading to increased fuel consumption. If you frequently tow near your truck's maximum capacity, a higher ratio is generally preferred.

• Numerically Lower Ratio (e.g., 3.42:1): With a lower ratio, the engine runs at lower RPMs at highway speeds. This reduces fuel consumption, making it more efficient for daily driving and lighter loads. While it still offers strong towing capabilities, especially when paired with the powerful Duramax diesel and 10-speed Allison, it won't have the same initial grunt for extremely heavy or challenging towing situations compared to a higher ratio.

For the 2020 Silverado 3500HD with the Duramax diesel and 10-speed Allison, the 3.42 axle ratio provides an excellent balance. The wide gear spread of the 10-speed transmission allows for both strong low-end torque for towing and efficient highway cruising. The 3.73 ratio is standard with the 6.6L gas engine, providing the necessary mechanical advantage for towing with that powertrain combination.

Common issues

While the Silverado 3500HD is built for durability, heavy use can sometimes lead to issues with the driveline components:

• Ring and Pinion Whine: This is often heard as a howling or whirring noise that changes with vehicle speed and load. It can indicate improper gear setup, wear, or damage to the ring and pinion gears within the differential.
• Carrier Bearing Wear: The carrier bearings support the differential carrier. Wear or damage to these bearings can manifest as a growling or rumbling noise, especially during acceleration or turns.
• Limited-Slip Differential Clutch Wear: If your Silverado is equipped with a limited-slip differential, the clutch packs can wear out over time, especially with hard use or infrequent fluid changes. Symptoms include a chattering or clunking noise from the rear end when turning, or a decrease in traction in slippery conditions.

Regular maintenance, including differential fluid changes at recommended intervals, can significantly extend the life of these components.

Find a driveline shop on Repairius.