AAM 11.5 Rear Differential Cover, Cast Aluminum 14-Bolt

If your Silverado or Sierra HD, or your Ram 2500 or 3500, is weeping gear oil around a rusty stamped rear cover, or you tow heavy and want the axle to run cooler, this cast aluminum cover is made for the American Axle 11.5 in. rear. It bolts to the 14-bolt AAM housing on 2001-2019 Silverado 2500 HD and Sierra 2500 HD, 2007-2019 Silverado and Sierra 3500 HD, 2003-2010 Ram 2500 and 3500 and 2011-2018 Ram 3500, and it comes with a gasket, bolts and washers. Part number ASPOS08833RD, red finish.

What a differential cover does on an AAM 11.5

On a full-floating heavy-duty axle like the 11.5, the rear cover is more than a lid. It seals the gear oil in, it is the first thing a rock or rut hits, and it is the surface the hot oil flung off the ring gear runs down before it heads back to the pinion bearings. The factory stamped steel cover is thin, holds only a modest amount of oil and tends to rust at the flange, which is where slow leaks start. This cover is a thick ribbed aluminum casting. The bulged back adds oil capacity, internal channels guide the oil thrown off the ring gear back toward the pinion and carrier bearings, and the outside fins add surface area to shed heat on long pulls. It also has separate fill and drain plugs and a sight window, so you can check and change gear oil without breaking the gasket seal again.

Symptoms that say the cover needs attention

• Wet, dirt-caked oil along the bottom of the cover flange or around a couple of bolt holes
• Rust scale or pitting at the cover lip, which keeps eating the gasket surface
• A dent pushed in toward the ring gear after a trail hit or a rutted job site
• Dark, burnt-smelling gear oil after towing, a sign the axle is running hot
• Having to pull the cover every oil change because the original has no drain plug

How to confirm before ordering

A leak at the cover is easy to mix up with a pinion seal leak or a hub seal leak on a full floater, so clean the axle and drive a few days to see where the oil starts. Our cover leak guide and pinion seal leak guide show the difference. Next, make sure the axle is the AAM 11.5 and not the older GM 10.5 corporate 14-bolt. Both have 14 cover bolts but the covers do not interchange; our 14-bolt vs AAM 11.5 comparison shows how to tell them apart. If you hear bearing noise as well, read the AAM 11.5 problems guide before buttoning it up.

Fitment

Listed for the AAM 11.5 in. rear axle (some catalogs call it the 11.8) under 2001-2019 Silverado 2500 HD and Sierra 2500 HD, 2007-2019 Silverado 3500 HD and Sierra 3500 HD, 2003-2010 Ram 2500 and 3500 and 2011-2018 Ram 3500. Trucks outside those years, and Ram 2500 models from 2011 on, are not on this listing, so send us your year and VIN before ordering. It is not for the GM 10.5 corporate 14-bolt; that axle takes the Hardcore 14-bolt cover instead. If you prefer a nodular iron armor cover for the same AAM axle, compare the ATS Protector for the 11.5. More axle hardware is in our hard parts category.

Install notes

• Drain the axle, remove the old cover and scrape the housing flange to clean metal. A rusty flange will leak through any gasket.
• Wipe both faces with brake cleaner, then set the supplied gasket. On a pitted flange, a thin bead of gear-oil-safe RTV on each side is cheap insurance.
• Run the bolts down with their washers in a crisscross pattern and bring them up evenly so the casting seats flat.
• Fill through the fill port to the sight window with the gear oil your owner's manual specifies. Because this cover holds more oil than stock, buy an extra quart. Add friction modifier only if your axle has a limited slip and the oil does not already contain it.
• With the cover off, it is the right time to look at the ring gear and bearings. Worn bearings call for the YK GM11.5-B overhaul kit, and leaking hubs take the AK GM11.5 bearing and seal kit.

Will this cover fit my 2015 Silverado 2500HD?

Yes, 2001-2019 Silverado 2500 HD and Sierra 2500 HD with the AAM 11.5 rear are on the listed fitment. Confirm you have the 11.5 and not a swapped axle by reading the axle tag or comparing ring gear size.

Does it fit the old GM 14-bolt 10.5 full floater?

No. Both axles have 14 cover bolts, but they are different housings and the covers do not interchange. The 10.5 corporate 14-bolt needs its own cover.

What comes in the box?

The cover, a gasket, cover bolts, spring washers and disc washers. It has a fill plug, a drain plug and an oil level sight window built in.

How much more gear oil does it take?

The bulged casting holds more than the factory stamped cover. Fill to the level shown on the sight window rather than counting quarts, and keep an extra quart on hand for the first fill.

Do I need RTV with the supplied gasket?

Not on a clean, flat flange. On an older truck with a pitted or rusty housing face, a thin bead of gear-oil-resistant RTV on both sides of the gasket helps it seal.

Should I add friction modifier?

Only if your axle has a limited-slip differential and the gear oil you are using does not already include the additive. An open differential does not need it.