ATS Diesel 01+ GM / 03+ Dodge 14-Bolt 11.5in American Axle ATS Protector Rear Differential Cover
Towing a fifth wheel or gooseneck behind a Duramax or Cummins puts more heat into the rear axle than anything else the truck does. The ATS Protector, part number 402-915-6248, replaces the thin stamped cover on the American Axle 11.5 with a cast aluminum cover that holds about 2.5 quarts more gear oil than stock and has a built-in heat sink to pull temperature out of it. It is aimed at owners of 2001-up Silverado and Sierra 2500HD and 3500HD trucks and Ram 2500 and 3500 trucks with the 11.5 rear who are chasing hot gear oil, a weeping cover gasket, or a dented factory cover.
The 11.5 is a full-float axle with an 11.5 in. ring gear and a large pinion, and its weak point is not the gears breaking. It is heat and bearing wear from long hours under load. Gear oil that runs hot thins out, oxidizes faster and stops protecting the pinion bearings, which is how a healthy axle turns into one with a whine at 55 mph. A bigger oil volume takes longer to heat up and has more capacity to carry that heat away, and the finned aluminum casting sheds it to the air passing under the truck. ATS finishes the cover in black powdercoat and puts a drain plug in it, so you can change the oil without pulling the cover and breaking the seal every service.
A cover will not fix bearings that are already worn. If the axle is already noisy, read our AAM 11.5 problems and rebuild cost guide first. The usual fix for a whining 11.5 is a full bearing job such as the Yukon master overhaul kit for 2010-and-down 11.5 or the USA Standard 11.5 overhaul kit, and the new cover goes on at the end of that rebuild.
The parts counter hears 14-bolt and gets it wrong all the time. The older GM Corporate 14-bolt full floater has a 10.5 in. ring gear and was used under GM three-quarter and one-ton trucks through about 2000. The AAM 11.5 replaced it in 2001 and also uses 14 cover bolts, but the cover outline is different and nothing crosses over. Count the bolts, check the build tag under a cover bolt, and compare the cover shape. Our GM 14-bolt vs AAM 11.5 guide shows how to tell them apart. Some 2003-2013 Hemi Ram 2500 trucks got the smaller AAM 10.5 instead, so check before ordering.
ATS lists this cover for 2001-up GM 2500HD and 3500HD trucks and 2003-up Ram 2500 and 3500 trucks with the AAM 11.5 rear. One authorized retailer adds that on the Ram side it fits only trucks with a rear leaf spring suspension, and that it will not clear rear coil-sprung applications. If you have a coil-spring rear Ram, send us the year and VIN before you buy. It is not for the older GM 10.5 Corporate 14-bolt or for any axle with independent rear suspension. More axle hardware is in our hard parts section.
If you are already into the axle for a traction upgrade, the Yukon Grizzly Locker for the 11.5 fits the same 30-spline axle.
| Brand | ATS Diesel |
| Part number | 402-915-6248 |
| Fits | ATS Diesel 01+ GM / 03+ Dodge 14-Bolt 11.5in American Axle ATS Protector Rear Differential Cover |
| Type | Diff Covers |
| Condition | New |
| Ships | Same business day (in stock), from the USA |
| Warranty | 1-year |
Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
Probably not. Most GM trucks through 2000 used the GM Corporate 14-bolt with a 10.5 in. ring gear, which has a different cover. This ATS cover is for the AAM 11.5 used from 2001 on GM HD trucks and 2003 on Ram HD trucks.
One authorized retailer notes it fits Ram trucks only with a rear leaf spring suspension and will not clear coil-sprung rears. If your Ram has rear coils, send us the year and VIN before ordering.
About 2.5 quarts more than the stock cover. Fill to the fill hole and expect to use more oil than you did with the factory cover.
Yes. The cover has a drain plug, so oil changes are drain and refill without disturbing the gasket.
Use 75W-90 or 75W-140 gear oil as your owner manual specifies for the 11.5. Add friction modifier only if the axle has a clutch-type limited slip that requires it.
No. A whine usually means worn pinion bearings or a gear pattern that has moved. The cover helps keep a healthy axle cool; a noisy one needs a bearing overhaul first.
