NP246 Transfer Case Rear Half Housing with New Seals

This is the rear half of the transfer case housing for the GM NP246, sold under Dorman part number 917-561 and cross-referencing the GM numbers SK917561, 12473226 and 12474949. It is a new die-cast aluminum casting, machined at the bearing bores and sealing faces, and it comes with the new seals needed to close the case back up. You reuse your own internals: planetary, chain, sprockets, shift fork, pump and output shaft all transfer over into this housing.

The reason this part exists is that the rear half is the half that fails. On the GM encoder-motor cases the oil pump sits against the inside of the rear housing, and over high mileage the pump body wears a groove into the aluminum until it breaks through. That is the classic pump-rub failure: fluid runs out the back of the case, the case starves, and the chain and planetary cook. The other common version is a straight crack or a weeping seam after an impact or a seized rear driveshaft. In either case the internals are usually still serviceable and only the casting needs to be replaced, which is far cheaper than a complete transfer case.

Fitment is select Cadillac, Chevrolet and GMC four-wheel-drive models. Buyers have confirmed it on the NP246 behind a 6.0L and 4L80E in a 2001 Silverado 2500HD, and on the NP261 in a 1999 GMC Sierra, which shares the same rear case half. Check the casting numbers on your own case against the GM numbers above before ordering, because GM used several closely related cases across these trucks.

On the bench: drain it, pull the rear output yoke and seal, split the halves, and move the internals over one at a time so the chain and sprockets go back in the same relationship. Inspect the rear output bearing and the pump wear area while it is open, since a housing that rubbed through has usually been running low on fluid for a while. Clean both sealing faces down to bare aluminum, lay a continuous bead of RTV, and draw the case bolts down evenly in a crossing pattern rather than going around the perimeter.