2017 Ford F-350 Super Duty Transmission & Axle Gear Ratios

Transmission gear ratios

The 2017 Ford F-350 Super Duty was offered with a single transmission option, the TorqShift 6-speed automatic.

TorqShift 6R140 Automatic Transmission

Available axle ratios

The 2017 F-350 Super Duty offered a range of axle ratios, allowing owners to optimize their truck for various demanding tasks from heavy towing to improved fuel efficiency. The availability of specific ratios could depend on the engine choice (6.2L V8 gasoline or 6.7L Power Stroke V8 turbo diesel) and trim level.

How to identify your axle ratio

Identifying the axle ratio of your 2017 Ford F-350 Super Duty is crucial for proper maintenance and understanding your truck's capabilities. There are several ways to determine this:

• Door-Jamb RPO Sticker: Open the driver's side door and look for a sticker on the door jamb. This sticker contains various codes, including the "AXLE" code. This two-digit code (e.g., 3L, 4L, 3.55) will correspond to your rear axle ratio and whether it's an open or limited-slip differential. For example, "3L" might indicate a 3.31 limited-slip, while "4L" could be a 4.10 limited-slip. Refer to a Ford decoding chart for exact matches.
• Axle Tag: Some F-350 models may have a metal tag attached to one of the differential cover bolts on the rear axle. This tag will often explicitly state the gear ratio (e.g., "3.55" or "4.10"). Be aware that these tags can become corroded or lost over time.
• VIN Decoder: You can use an online VIN decoder service. Many Ford-specific decoders can provide detailed build information, including the original axle ratio installed from the factory.

Towing vs MPG impact

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

• Numerically Lower Ratios (e.g., 3.31, 3.55): These ratios mean the engine rotates fewer times for each rotation of the wheels. This results in lower engine RPMs at highway speeds, leading to better fuel economy. However, with less mechanical advantage, the engine has to work harder to get a heavy load moving and maintain speed, which can reduce towing capacity and acerbate engine strain when towing near maximum limits.
• Numerically Higher Ratios (e.g., 3.73, 4.10, 4.30): With these ratios, the engine rotates more times for each rotation of the wheels. This provides a greater mechanical advantage, making it easier to start and tow heavy loads and reducing strain on the engine and transmission. The trade-off is higher engine RPMs at highway speeds, which typically results in decreased fuel economy.

For a 2017 F-350 Super Duty, if your primary use involves frequent, heavy towing, a numerically higher ratio like 3.73 or 4.10 (or even 4.30 with the gas engine) would be beneficial. If your truck is more of a daily driver with occasional light hauling, a 3.31 or 3.55 ratio might offer a better balance of power and efficiency.

Common issues

While Ford Super Duty axles are generally robust, a few common issues can arise over time, often exacerbated by heavy use or lack of maintenance:

• Ring & Pinion Whine: A persistent high-pitched whine that changes with vehicle speed (not engine RPM) often indicates wear or improper setup of the ring and pinion gears. This can be caused by insufficient lubrication, heavy towing without adequate cooling, or improper backlash adjustment during an earlier repair.
• Carrier Bearing Wear: The carrier bearings support the differential carrier within the axle housing. Worn carrier bearings can produce a low growling or roaring noise that gets louder with speed. This wear can be accelerated by heavy loads, aggressive driving, or contaminated differential fluid.
• Limited-Slip Clutch Wear: Many F-350 models come with a limited-slip differential. Over time, the clutch packs within these differentials can wear out, leading to a loss of traction assistance and potentially chattering or clunking noises during turns. Regular differential fluid changes with the correct friction modifier are essential to prolong the life of these clutches.

Regular inspection of differential fluid for contamination or low levels, along with listening for unusual noises, can help catch potential issues early and prevent more costly repairs.

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