2007.5-2010 GMC Duramax LMM Front Differential Covers

The AAM 9.25 front axle under the 2007.5-2010 Sierra HD

GMC used American Axle's 9.25-inch independent front differential on every 4x4 Sierra 2500HD and 3500HD of the LMM era, whether it left the lot as a WT, an SLE or an SLT. The two-piece clamshell housing holds about 1.82 quarts of 80W-90 gear oil and drives CV axles under the torsion-bar suspension. Ratios from 3.42 to 4.56 were listed for this axle, while Duramax Sierras paired 3.73 gears front and rear as the standard setup.

Where it shows strain

In stock form the 9.25 does an adequate job. It is still more wear-prone than a solid axle, and larger tires, extra power and frequent hard off-road use bring that out fast. Listen for noise from the front diff, and watch for CV or seal leaks and bearing wear after you upsize. At 37 inches the 3.73 gears become a mismatch: the transmission hunts, the engine lugs, and fuel mileage and towing performance fall off.

Keep it stock or build it up

If your Sierra still rolls on factory-size tires, the front-axle job is simple: the right oil at the right level. Planning on 37s? Plan on gears in the 4.30-4.56 range as well, set the same in both axles, because a 4x4 needs matching front and rear ratios.

What we carry

The part here is the 402-009-1000 drain plug from ATS Diesel Performance. It is made for ATS pans and ATS differential covers, which makes it a service part for a Sierra already running ATS hardware rather than a piece for the factory clamshell. If the plug on your ATS cover is lost or damaged, this is the one to order.

Fitment notes

Front axle parts apply to 4x4 Sierras only. Because the front differential was redesigned for 2011, parts built for a 2011-or-newer Sierra HD will not fit the 9.25 under a 2007.5-2010 truck. Settle ratio questions by RPO code or VIN, and verify fitment by VIN or with the fitment checker before you order.

Frequently asked questions

Is the ATS 402-009-1000 a front differential cover?

No. It is a drain plug that fits ATS pans and ATS differential covers. Order it when your Sierra already runs ATS hardware and the plug needs replacing.

I am putting 37-inch tires on my Sierra 2500HD. What changes up front?

The 9.25 works harder, and larger tires are what expose its weak spots: diff noise, CV and seal leaks, and bearing wear. The factory 3.73 gearing also becomes a mismatch at 37 inches. The usual answer is a re-gear to roughly 4.30-4.56 in both axles.

Do the front and rear gear ratios have to match on my Sierra?

Yes. On a 4x4 the front and rear ratios must be the same, and 3.73 is the standard combination on Duramax trucks. Confirm yours by RPO code or VIN before ordering gears or gear-related parts.

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.