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Call or Text (352) 722-5295Differentials on the 2003-2004 Dodge Ram 5.9L Cummins
The rear axle behind the 5.9L Cummins is the AAM 11.5: an 11.5 in ring gear, 30-spline shafts, 3.42, 3.73 or 4.10 gearing, and about 3.8 qt of synthetic gear oil. Four-wheel-drive trucks add an AAM 9.25 solid front axle. That front axle shares a number with GM's 9.25 independent front differential but not its parts, so shop by Dodge fitment rather than by ring-gear size.
What wears and what to watch
These differentials aren't a known problem. No pattern failure has been sourced for the AAM rears, and the warning sign that one has been neglected is a whine or howl from running low on fluid. So the work here is service. The factory schedule's severe-service interval is 15,000 miles, with 75W-90 GL-5 synthetic up front and 75W-90 or 75W-140 synthetic in the rear. A cover gasket, a bolt kit and a drain plug are on this page so the cover goes back on right after a fluid change.
Stock cover or aftermarket cover
If the truck tows, a finned aluminum cover is the upgrade worth a look. Finned covers from Mag-Hytec and aFe add fluid capacity and a drain and fill, and they're aimed at towing trucks running 75W-140. PPE's heavy-duty cast aluminum covers, the BD Diesel and WCFab covers and the Banks Ram-Air cover kit are the other options. For a truck that sees light duty, a fresh fill of the right grade at the right interval does most of the work.
What we carry
- Front covers (AAM 9.25): Mag-Hytec AA14-9.25-A, the Pacific Performance Engineering 9.25 in heavy-duty cast aluminum cover and the BD Diesel 1061826.
- Rear covers: Mag-Hytec AA 14-11.5, the PPE AAM 11.5 heavy-duty cast aluminum cover, BD Diesel 1061825, Wehrli Custom Fabrication WCF100113, the Banks Power Ram-Air differential cover kit and the aFe 46-70032.
- Sets and hardware: the BD Diesel 1061827 front-and-rear pack, the PPE 138051002 rear cover gasket, the WCFab WCF100217 cover bolt kit and the ATS Diesel Performance 402-009-1000 drain plug.
- Gear oil: Hot Shot's Secret, Lucas Oil and Royal Purple.
Fitment notes
Check three things. First, the Mag-Hytec AA 14-10.5 is for the 10.5 rear, which is normally a gas-2500 axle; buy it only if your tag reads 10.5. Second, the aFe 46-70032 is a Dana 80 cover, and Dodge moved off Dana axles for 2003, so it fits only a truck that has had a Dana 80 put under it. Third, many 11.5 covers list Duramax years as well as Cummins; that is a cover made for the AAM 11.5, not a reason to cross-reference older GM 14-bolt 10.5 parts, which have a smaller ring gear. When the truck's history is unclear, verify by VIN.
Frequently asked questions
How much gear oil does the 11.5 rear take?
About 3.8 qt of 75W-90 or 75W-140 synthetic with the factory cover. A larger aftermarket cover adds capacity, so fill to the level the cover maker specifies.
Can I put a GM 9.25 cover on my Ram's front axle?
No. The Dodge AAM 9.25 is a solid front axle, and it differs from the GM 9.25 independent front unit despite the shared size. Use covers listed for Dodge/Ram Cummins trucks, like the ones on this page.
Why do some 11.5 covers list Duramax trucks too?
Because the cover is built for the AAM 11.5 axle, and the product titles show both Duramax and Cummins years. What you should not do is cross-reference GM 14-bolt 10.5 parts; the 11.5 ring gear is larger.
Do I need the 10.5 cover or the 11.5 cover?
Almost always the 11.5. The AAM 11.5 is the Cummins rear, and the 10.5 is the gas-2500 axle. If the truck is used or has had axle work, read the tag first.
Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.