2007.5-2010 GMC Duramax LMM Axle & Driveline Parts

How the LMM Sierra HD driveline is put together

GMC built these trucks on the GMT900 heavy-duty platform from mid-2007 through 2010, in WT, SLE and SLT trim. If the badge says Denali HD, you are looking at a 2011 or newer truck with the LML, not an LMM. The LMM's 365 hp and 660 lb-ft go through the Allison 1000 six-speed and into the rear axle, and that rear is the AAM 11.5: 11.50-inch ring gear, 30-spline shafts, a 14-bolt cover, 3.8 to 4.2 quarts of 75W-90 full synthetic. GM's Sierra brochure lists 3.73 as the standard rear ratio on both 2500HD and 3500HD and shows the 4.10 as a Vortec 6.0L gas combination. The Eaton heavy-duty automatic locking rear differential was optional, and standard on the 3500HD two-wheel-drive regular cab long box and on SLT. Four-wheel-drive Sierras also carry the AAM 9.25 front differential, a two-piece clamshell case holding 1.82 quarts of 80W-90, with factory ratios listed from 3.42 up to 4.56 across these years.

Where these axles give trouble

Lifted Sierras are where the front end shows its limits. The 9.25 clamshell holds up fine at stock tire size and stock power, but once a truck is on larger tires, making more torque, or working hard off pavement, it wears faster than a solid front axle would. Whining from the front differential, CV and seal leaks and bearing wear are what owners commonly report after a lift-and-tire job, not at a set odometer reading. The second problem is purely gearing: 3.73s do not suit 37-inch tires, so the truck lugs, the transmission shifts more than it should, and towing and fuel mileage both get worse. Neither one is a reason to distrust the rear axle, since the 11.5 is the stout end of the truck, but both are reasons to plan the whole job instead of buying one part.

Replace it stock, or upgrade it

If a cover is weeping at the gasket and the Sierra is stock, a gasket and fresh fluid is the whole repair. If the truck tows, whether that is a dually dragging a gooseneck or an SLT crew cab with a fifth-wheel on the hitch, a finned cast-aluminum cover is the upgrade that matters, because it adds fluid volume and cooling surface to the AAM 11.5 for exactly that duty. Gear oil goes with it, and the rear axle is specified on a full-synthetic 75W-90. If the truck is already on 37s, the real upgrade is a ring-and-pinion change in the 4.30 to 4.56 neighborhood, done at both ends so the ratios stay matched.

What we carry on this page

AAM 11.5 rear differential covers in cast aluminum from PPE, Mag-Hytec, Wehrli Custom Fabrication, BD Diesel and AFE, plus the Banks Power Ram-Air cover kit. The small parts that go with them are stocked too: a PPE rear cover gasket, a WCFab cover bolt kit and an ATS Diesel Performance drain plug for their pans and covers. Merchant Automotive speed sensor connectors are here for a damaged speed sensor pigtail. For fluid, Hot Shot's Secret Blue Diamond and ADRENALINE gear oil, Lucas Oil synthetic and heavy-duty gear oil, and Royal Purple Max-Gear, in grades from 75W-90 to 85W-140. More for the platform sits under the Duramax hub.

Fitment notes

Identify the axle first. A 14-bolt cover on the back of the housing is the AAM 11.5, and that is what every cover and gear set on this page is cut for. On a 4x4 the front and rear ratios must match, with 3.73 at both ends being the standard Duramax combination, so if a previous owner re-geared one end, match what is in the truck rather than what the brochure says. Treat a 4.10 claim as something to verify by RPO code or VIN, since GM's own brochure pairs that ratio with the gas engine. Across 2010 to 2011 nothing is safe to assume: the front differential was redesigned for 2011 so 2001-2010 9.25 parts do not interchange, and the 2011 HD trucks also got a new frame, new control arms, new torsion bars and new rear springs. Single- and dual-rear-wheel 3500HD trucks differ at the wheel end even though the axle itself is the same. Use the fitment checker on any product page, or give us the VIN.

Frequently asked questions

How do I know whether my Sierra has the AAM 11.5 rear axle?

Count the bolts around the differential cover. Fourteen bolts is the AAM 11.5, which is what GM put under 2500HD and 3500HD trucks through this generation, single or dual rear wheel. Confirm it before you order a cover or a gear set, since covers are machined to the housing.

Does a dually need a different differential cover than a single-rear-wheel truck?

No. The rear axle is the same AAM 11.5 on SRW and DRW 3500HD trucks, so the 14-bolt cover is the same part. What changes between the two is the wheel end and the track width, not the housing. If you are not sure which truck you have, the fitment checker or your VIN will settle it.

What ratio did my 2009 Sierra 2500HD leave the factory with?

GM's Sierra brochure lists 3.73 as the standard rear ratio on 2500HD and 3500HD, and shows the 4.10 as a Vortec 6.0L gas combination. The aftermarket does talk about 4.10 Duramax trucks, so read the RPO tag or have us check the VIN rather than assuming. On a 4x4 the front has to match whatever the rear is.

Will LMM axle parts fit a 2011 or newer Sierra Denali HD?

Front differential parts will not. GM redesigned the front clamshell for 2011, and 2001-2010 AAM 9.25 pieces are their own family. The 2011 trucks also moved to a new frame and front suspension, which is why we keep 2007.5-2010 parts on their own pages. Shop this page for an LMM truck, and call us if you are buying for a newer one.

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.