2007.5-2010 GMC Duramax LMM Rear Differential Covers

The rear axle under your 2007.5-2010 Sierra HD LMM

GMC built every LMM Sierra HD on American Axle's 11.5-inch full-float rear. It runs an 11.5-inch ring gear and 30-spline shafts behind a 14-bolt cover, and it holds 3.8 to 4.2 quarts of SAE 75W-90 full-synthetic gear oil. GMC's 2009 brochure lists 3.73 as the standard ratio and the Eaton heavy-duty automatic locking rear differential as optional, with the locker standard on the SLT and on the 3500HD 2WD regular cab long box.

Covers as a towing upgrade

Swapping to a finned aluminum cover adds fluid capacity and cooling for towing. Think of an SLE pulling a gooseneck, or a WT with a loaded equipment trailer behind it. Re-gearing for 37-inch tires, usually to around 4.30-4.56, means the cover comes off anyway, so that is a natural time to make the change.

What we carry

Covers first: the Banks Power Ram-Air Differential Cover Kit, the aFe Street Series 46-71060A and Pro Series 46-71060B, the Mag-Hytec AA 14-11.5, the heavy-duty cast aluminum AAM 11.5 cover from PPE, the WCFab WCF100113 and the BD Diesel 1061825. Service parts round it out: PPE's 138051002 rear cover gasket, a WCFab cover bolt kit and the 402-009-1000 drain plug from ATS Diesel Performance, which fits ATS pans and covers.

Fitment notes

Before ordering, find the 14-bolt cover on the back of the axle; it identifies the AAM 11.5. The PPE, Mag-Hytec, Banks and WCFab cover titles list 2001-2019 Duramax and BD lists 2001-2018, so every LMM year falls inside them. The WCFab WCF100217 bolt kit carries its own year range, so check it against your Sierra before adding it to the cart. Verify by VIN or use the fitment checker.

Frequently asked questions

Will a cover listed for 2001-2019 Duramax fit my 2009 Sierra 3500HD?

Yes, as long as the axle wears the 14-bolt cover of the AAM 11.5, which every LMM Sierra HD does. The 2007.5-2010 trucks sit inside that 2001-2019 range. Still verify by VIN or use the fitment checker for your exact truck.

Does my Sierra SLT have a locking rear differential?

Likely. GMC's 2009 brochure lists the Eaton heavy-duty automatic locking rear as standard on SLT and on the 3500HD 2WD regular cab long box, and optional on other trucks. Confirm with your build sheet or VIN.

Should I replace the gasket when I swap covers?

Plan on a fresh seal when the new cover goes on. PPE's 138051002 gasket is listed for 2001-2019 Duramax rear covers; check whether your new cover ships with one before ordering. Refill with SAE 75W-90 full synthetic, and expect a finned cover to take more than the stock 3.8 to 4.2 quarts.

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.