2018 Ford F-350 Super Duty Transmission & Axle Gear Ratios

Transmission gear ratios

The 2018 Ford F-350 Super Duty was offered with two robust transmission options, each designed to handle the demanding tasks expected of a heavy-duty truck.

TorqShift G 6-Speed Automatic (6R100)

This transmission was typically paired with the 6.2L SOHC V8 engine, providing a balance of hauling capability and everyday driveability.

TorqShift 6-Speed Automatic (6R140)

The heavy-duty 6R140 transmission was standard with the 6.7L Power Stroke V8 Turbo Diesel engine and available with the 6.2L V8. It's engineered for maximum durability and towing performance.

Available axle ratios

Ford offered a variety of axle ratios for the 2018 F-350 Super Duty, allowing buyers to custom-tailor their truck for specific applications, from fuel efficiency to maximum towing.

How to identify your axle ratio

Identifying your F-350's axle ratio is crucial for proper maintenance, upgrades, and understanding its performance characteristics. For Ford trucks, the easiest way to find this information is on the door-jamb sticker located on the driver's side door frame. Look for the "AXLE" code. This code corresponds to one of the ratios listed above. Alternatively, you might find an axle tag bolted to one of the differential cover bolts on the rear axle. This metal tag will often have the ratio stamped directly on it (e.g., "3 73" for 3.73:1). If neither of these methods works, a Ford dealership can decode your VIN to provide the original build specifications.

Towing vs MPG impact

The axle ratio significantly impacts both towing capability and fuel economy. Generally, a numerically lower axle ratio (e.g., 3.31:1) means the engine operates at lower RPMs at a given road speed. This translates to better fuel economy on the highway and quieter cruising. However, it also means less mechanical advantage for towing heavy loads, potentially leading to the transmission downshifting more frequently or the engine working harder.

Conversely, a numerically higher axle ratio (e.g., 4.30:1) allows the engine to rev higher at a given road speed. This provides greater torque multiplication to the wheels, making it ideal for heavy towing and hauling. The trade-off is typically reduced fuel economy, especially at highway speeds, as the engine is working harder to maintain the same speed.

Choosing the right axle ratio depends on your primary use case for the truck. If you frequently tow heavy trailers or carry substantial payloads, a higher ratio might be more beneficial. For those who primarily use their F-350 for lighter duty or long highway commutes, a lower ratio could save you money at the pump.

Common issues

While the Ford F-350 Super Duty is known for its robust drivetrain, certain components can experience wear over time:

• Ring and Pinion Whine: A persistent high-pitched whine that increases with vehicle speed can indicate wear on the ring and pinion gears within the differential. This is often due to improper lubrication, incorrect backlash settings, or heavy use.
• Carrier Bearing Wear: The carrier bearings support the differential carrier. Worn bearings can present as a rumbling or growling noise, especially when accelerating or turning. If left unresolved, it can lead to further differential damage.
• Limited-Slip Clutch Wear: Many F-350s are equipped with a limited-slip differential. Over time, the clutch packs within these differentials can wear out, leading to a loss of limited-slip function (one wheel spinning freely) or chattering/binding during turns.

Regular differential fluid changes and inspection can help prolong the life of these components and identify potential issues early.

Find a driveline shop on Repairius.