4L60E Transfer Case Adapter Housing, Dorman 926-890

This is the aluminum adapter housing that sits between a GM 4L60E or 4L65E and the transfer case on full-size 4x4 trucks and SUVs. Dorman part number 926-890, replacing GM 15724744. The kit ships with the adapter, the adapter-to-case gasket and the output seal, so the joint goes back together with fresh sealing surfaces instead of the flattened original gasket.

The adapter is the piece that cracks. It carries the entire overhung weight of an NP246 or NP263 transfer case on a bolt flange, and years of driveline vibration, a loose transfer case mount, or a hard hit off-road put a hairline crack through the casting or snap a bolt boss off. The symptom is ATF dripping from the seam between transmission and transfer case, or a slow, unexplained loss of fluid that eventually cooks the 3-4 clutch pack. Chasing that leak by replacing the output seal alone gets you nowhere if the casting itself is split.

Fitment covers 1999-2006 Chevrolet Silverado 1500 and GMC Sierra 1500, 1999-2001 Silverado and Sierra 2500, 2001-2003 Sierra 1500 HD, 2007 Silverado and Sierra 1500 Classic, 2000-2007 Tahoe, Yukon and Yukon XL 1500, 2000-2007 Suburban 1500, 2002-2007 Avalanche, 2002-2006 Cadillac Escalade, Escalade ESV and Escalade EXT, 2003-2014 Express 1500 and Savana 1500, and 2003-2007 Hummer H2. Adapter lengths vary within those years, so measure your original face to face and match the casting number before you order.

On the bench, support the transfer case, pull it off the adapter, then unbolt the adapter from the transmission case. Clean both mating faces down to bare aluminum, set the new gasket dry, and torque the adapter bolts evenly in a cross pattern. Drive the new output seal in square and lubricate the lip before the transfer case input slides through it. If the original cracked from vibration, inspect the transfer case mount and driveshaft U-joints before you close it up, or the replacement takes the same beating.