2018 Ford F-250 Super Duty Transmission & Axle Gear Ratios

Transmission gear ratios

The 2018 Ford F-250 Super Duty was offered with two transmission options: the TorqShift G 6-speed automatic and the TorqShift 6-speed automatic.

TorqShift G 6-speed Automatic (6R100)

This transmission was typically paired with the 6.2L V8 gasoline engine.

TorqShift 6-speed Automatic (6R140)

This heavier-duty transmission was standard with the 6.7L Power Stroke V8 Diesel engine and optionally available with the 6.2L V8 gasoline engine.

Available axle ratios

The 2018 F-250 Super Duty offered a range of axle ratios to suit various needs, from fuel economy to heavy-duty towing.

Note: Specific availability may vary based on trim level, cab configuration, and driveline (2WD/4WD). Always verify with your vehicle's documentation.

How to identify your axle ratio

Knowing your F-250's axle ratio is crucial for understanding its performance characteristics. Here's how to find it:

• Door-Jamb RPO Sticker: Locate the white sticker on the driver's side door jamb. Look for the "AXLE" code. This code will correspond to your installed axle ratio and, in some cases, differentiate between open and limited-slip differentials. Ford's codes are often two characters (e.g., "3L" for a 3.31 electronic locker, "35" for a 3.55 open differential).
• Axle Tag: Some F-250s may have a metal tag attached to one of the differential cover bolts. This tag will directly state the gear ratio (e.g., "3.55"). However, these tags can become corroded or go missing over time.
• VIN Decoder: A Ford dealership or online VIN decoder service can often provide a detailed build sheet for your specific vehicle, which will include the axle ratio.

Towing vs MPG impact

The choice of axle ratio significantly impacts your truck's towing capability and fuel efficiency.

• Numerically Lower Ratios (e.g., 3.31:1): These ratios mean the engine rotates fewer times for each revolution of the wheels. This generally results in better fuel economy during unloaded highway driving. However, it requires the engine to work harder to get a load moving, reducing towing capacity and accelerating slower, especially with heavy trailers.
• Numerically Higher Ratios (e.g., 4.10:1, 4.30:1): These ratios cause the engine to rotate more times for each wheel revolution. This provides more torque multiplication at the wheels, making it easier to start and pull heavy loads. This translates to increased towing capacity and better acceleration, but at the expense of higher engine RPMs at highway speeds, leading to decreased fuel economy.

For the 2018 F-250, a 3.55:1 or 3.73:1 ratio generally offers a good balance for owners who tow occasionally but also use their truck for daily driving. If heavy towing is a regular occurrence, opting for a 4.10:1 or 4.30:1 ratio will provide superior performance and reduce strain on the powertrain, though you'll likely see a dip in your MPG.

Common issues

While the Super Duty axles are generally robust, some issues can arise:

• Ring and Pinion Whine: A persistent high-pitched whine that changes with vehicle speed and throttle input can indicate wear on the ring and pinion gears. This often necessitates gear replacement.
• Carrier Bearing Wear: The bearings supporting the differential carrier can wear out, leading to a growling or humming noise, especially when accelerating or turning. If left unaddressed, this can lead to more significant damage.
• Limited-Slip Clutch Wear: For models equipped with mechanical limited-slip differentials, the internal clutch packs can wear over time. Symptoms include a chattering or clunking noise from the rear end during turns, especially at low speeds. This can often be remedied by replacing the clutch packs.

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