NP261 NP263 Transfer Case Bearing & Seal Kit (ZTBK371)

This is the USA Standard Gear ZTBK371 bearing, gasket and seal kit for the New Process 261LD, 261HD and 263HD transfer case, 1995 and newer. Those are the cases bolted behind the 4L60E, 4L80E, Allison 1000 and NV4500 in GM half-ton, 2500 and 3500 trucks and the full-size SUVs, and this is what you open when the case starts to whine, growl on the highway, or drip gear oil down the crossmember.

The kit uses the 1.575 in ID rear mainshaft bearing, so check that dimension against what came out before you order - New Process ran more than one mainshaft bearing size across the 261/263 family and the rear bearing is the one that tells them apart. Along with the bearing set you get the gaskets and the seals: front and rear output seals, the front input seal, and the case half gasket or sealing surface hardware needed to put it back together dry.

On the bench, this is a bearing-and-seal overhaul, not a chain and sprocket kit. Split the case, pull the mainshaft, press the old bearings off and the new ones on, and inspect the drive chain for stretch and the oil pump for the classic 261/263 pump rub that eats through the rear case half. If the chain is loose or the case is worn through at the pump, add those parts before you close it up - a bearing kit will not fix a stretched chain or a holed case.

Common symptoms that lead here: a growl that changes with vehicle speed but not engine speed, gear oil on the rear output yoke, front output shaft seal leaks onto the front driveshaft, and roughness felt through the floor in 2WD that gets worse when loaded.