Axles - Differentials | 2003-2004 Ram 5.9 Cummins

Beginning in model year 2003, Ram went away from Dana as their axle supplier and moved to AAM, American Axle Manufacturing, which had already been adopted by GM for use in their heavy duty applications. Up front, Ram's are treated with a 9.25", while the rear receives an 11.5". From the factory, these housings were stuffed with either the popular 3.73 ratio, or the 4.10 most commonly used for heavy duty towing, as it delivers higher RPM's at lower speeds in comparison to the 3.73 ratio.

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 3.73 ratio, designed to have a proper run out with a stock size tire (roughly 31"). But as soon as you upgrade to a 35" 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 4.45 gear ratio (3.73/31*37). Unfortunately, in this scenario there is no such thing as a 4.45 ratio, but the closest would be a 4.56 that is readily available. Or, you can also opt to go with a slightly higher ratio of 4.10 that would give you a lower RPM vs. speed compared to stock.

Besides replacing the ring and pinion, we also offer numerous other upgrades, such as ARB Air Lockers, larger axles, rebuild kits, axle trusses for those that like to get airborn, 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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