Axles - Differentials | 2017-2019 Ford 6.7 Powerstroke

The release of the 2017 SuperDuty brought about some revisions to the axles in order to support the additional power and towing capacity compared to the previous 2011-2016 model year generation. Up front, its basically unchanged with the use of a 35 spline Super Dana 60. Out back, however, there are several variations depending on the capacity of the truck. For those with an F-250, there are two axles that could be residing under your bed. If your truck is equipped with the Heavy Duty Tow Package, you've got a Dana M275 featuring a 10.8" ring gear. For those F-250's without the HD Tow Package, you'll have the tried and true Sterling 10.5 that has been used for years, still featuring a 10.5" ring gear. Moving from there, the F-350 Single Rear Wheel (SRW) models are equipped with the same Dana M275 as the properly equipped 250's. Next, Dual Rear Wheel (DRW) F-350 and F-450's are bumped to a Dana M300 with a massive 11.8" ring gear. The 10.5" has 35 spline axles, where the M275 has 36 splines, and the M300 boasts 37 splines. From the factory, these housings were typically stuffed with the popular 3.31 ratio, but also had options for 3.55, 3.73, or 4.30 ratios.

Over the years, these assemblies have proven themselves relatively reliable on moderately used trucks running stock, or close to stock tire size and power output. For those of us that demand substantial power increases and larger tires, there is room for improvement to improve the reliability and performance that they can afford. One of the best upgrades we can recommend for anyone that has increased tire size, is that of a ring and pinion ratio upgrade. As previously stated, most of these trucks came factory with a 3.31 ratio, designed to have a proper run out with a stock size tire (roughly 32" with the popular 275-65R-18 size). But as soon as you upgrade to a 37" or larger tire, all of a sudden your RPM vs. speed are effected, even causing a disruption of the shift pattern on automatic transmission equipped trucks.

Lets give the example of upgrading to a 37" tire. By using cross multiplication, we can determine that in order to have the same RPM vs. speed as with the factory tire size, you would want to install a 3.83 gear ratio (3.31/32*37). Unfortunately, in this scenario there is no such thing as a 3.83 ratio, but the closest would be a 3.73 that is readily available. Or, you can also opt to go with a slightly lower ratio of 4.10 that would give you a higher RPM vs. speed compared to stock, which is especially useful for those towing frequently.

Besides replacing the ring and pinion, we also offer numerous other upgrades, such as ARB Air Lockers, rebuild kits, and so much more. As always, if you have any questions about which product is right for you and your truck don't hesitate to give us a call or send us an e-mail to [email protected] and we would be happy to help.

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