USA Standard NP231 Wide Input Transfer Case Bearing Kit

This is the USA Standard Gear ZTBK231 bearing and seal kit for the New Process 231 (NP231/NV231) chain-drive, part-time transfer case, in the wide-input version that uses the 24mm (0.94 in) input bearing. The NP231 sits behind the transmission on a long list of 4WD trucks and SUVs, and it is the case most people are rebuilding when a 4x4 develops a growl that changes with vehicle speed, a front output shaft that drips onto the driveshaft, or a chain that slaps on decel.

The kit replaces the wear items that kill an NP231: the input, mainshaft, and front/rear output bearings, plus the front and rear output shaft seals, the input seal, and the case-half gasket set. It does not include the drive chain, sprockets, or the oil pump, so if your chain is stretched or the pump housing is scored you order those separately. Match the input bearing width before you buy: the NP231 was built with both a wide (24mm) and a narrow input, and this kit is the wide-input set. If yours measures the narrow input you want the narrow kit instead.

On the bench you drain it, split the case, and press the old bearings off the input shaft, mainshaft, and output. Drive the new bearing races into the case halves, press the bearings on, set the new seals in the output housings and input bore, lay down the fresh case gasket, and torque it back together. Doing all the bearings and seals in one pass is the point of the kit, since pulling a transfer case to change one leaking seal and leaving tired bearings in it is the mistake that brings it right back to the bench.

USA Standard part number ZTBK231, alloy-steel ball bearings, backed by a 2-year warranty against manufacturer defects. Ships from the USA, handling in 1-2 business days.