Bolt-in replacement for the rusted transmission support crossmember on 2001-2010 Silverado and Sierra 2500HD, replaces GM 15904054.
If the crossmember under your Silverado or Sierra 2500HD has rusted thin where the transmission mount bolts through, you are probably feeling it already: a clunk when the truck shifts from park to drive, a driveline shake that comes and goes, or a tailshaft that visibly moves when someone brakes the engine against the converter. This is a bolt-in replacement center crossmember, Dorman 926-980, made to replace GM 15904054 and 25814670 on the GMT800 and GMT900 three-quarter and one-ton trucks that carry the Allison 1000 behind the Duramax or 8.1L, and the 4L80E behind the 6.0L gas engine.
The Allison 1000 is a long, heavy case, and on a 4x4 it also carries the transfer case hanging off the back. The engine mounts hold the front of that assembly; the crossmember spans the frame rails and holds up the rear through the transmission mount. Every bit of torque reaction from a diesel launching a loaded trailer goes through that mount and into this channel. When the steel is solid, the driveline stays at its designed angle. When the channel rots and the mount bolts start pulling through, the whole powertrain can sag and rock, which changes driveshaft angles and loads parts that were never meant to carry the weight.
Get the truck on a lift, put a pry bar between the crossmember and the transmission mount, and watch while a helper shifts between drive and reverse with a foot on the brake. Movement at the mount rubber points to the mount; movement where the mount meets the crossmember, or rust you can push a screwdriver through, means the crossmember is the problem. Do not mistake a driveline clunk for an internal transmission failure. If the truck also has shifting complaints, a flashing light or a stuck gear, read our Allison 1000 limp mode guide before you spend money on the wrong end of the truck.
The listing covers the Chevrolet Silverado 2500 HD 2001-2010, Silverado 3500 2001-2006, Silverado 3500 HD 2007-2010, Suburban 2500 2008-2013, Suburban 3500 HD 2016-2019, GMC Sierra 2500 HD 2001-2010, Sierra 3500 2001-2006, Sierra 3500 HD 2007-2010, and Yukon XL 2500 2008-2013. GM's own catalog lists 15904054 for 2001-2010 Silverado 2500 and 3500 with the 6.0L, 6.6L diesel and 8.1L. The frames changed between the GMT800 (2001-2007 Classic) and GMT900 (2007.5-2010) trucks, and cab-and-chassis models can differ, so compare the old crossmember's shape and bolt holes before you install, or send us your year and VIN. More parts for these trucks are in the Allison 1000 collection and the 4L80E collection.
Support the transmission with a transmission jack or a jack and wood block under the pan rail, not the pan itself. Remove the mount-to-crossmember nuts, then the frame bolts, and drop the old member out; on rusty trucks expect to cut or replace seized hardware. The new crossmember uses the factory frame holes with no cutting or welding. It is stamped steel with an epoxy coating, measures about 43.5 inches long and weighs about 28 lb. The transmission mount is not included, and a mount that has been sitting on a rotten crossmember is usually cracked, so plan to replace it. Torque the fasteners to the factory specification for your truck and check driveshaft angles before lowering it. While you are under there on a 2001-2007 4x4, look at the transfer case adapter; a transfer case brace is cheap insurance against a cracked housing. If cooler lines were stretched or rubbed by the sagging transmission, a braided cooler line kit is worth doing at the same time.
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Doing this repair right usually means replacing these at the same time. Same transmission, ships together.
No. The transmission mount is sold separately. Most mounts that sat on a rusted crossmember are torn or compressed, so replacing it at the same time is the usual move.
The 2008 Silverado 2500 HD is in the listed fitment, and GM lists 15904054 for 2001-2010 2500 and 3500 trucks with the 6.6L diesel. Compare the old part's shape and bolt holes, or send us your year and VIN to confirm.
No. It bolts to the original frame holes. You may need to cut seized factory bolts on a rusty truck, so have new hardware on hand.
Yes. GM catalogs the same crossmember for 6.0L and 8.1L gas HD trucks as well as the Duramax, so it covers 4L80E and Allison 1000 trucks within the listed years.
No. The listed fitment ends with the 2010 Silverado and Sierra HD pickups (and the 2019 Suburban 3500 HD). The 2020 and later HD pickups were redesigned and use the 10L1000 ten-speed instead of the Allison 1000.
