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The NP261 and NP263 are GM's heavy-duty, chain-driven transfer cases found behind the Allison 1000 and 4L80E/4L85E on 2500/3500-series Silverado, Sierra, Suburban, and Tahoe trucks, including Duramax diesels. NP261 is the full-time (Autotrac) version and NP263 is the part-time version, but the two share the same case, bearings, and seals, so parts cross freely between them.
Match your symptom to the right part below before you buy. A bearing and seal kit will not fix an electrical shift-motor fault, and a shift motor will not stop a fluid leak.
Three Problems, Three Different Parts
1. Bearing & Seal Kit — Fluid Leaks, Whining, General Wear
Covers the input and output shaft bearings and the case seals. This is the right call if the truck is dripping fluid from the case, you hear a bearing whine that tracks with road speed, or you are doing a preventive rebuild on a high-mileage case that has never been opened. We stock two versions at different price points depending on bearing brand and kit contents.
Typical cost: $130-210 for the kit. Figure 4 to 6 hours of labor for a shop to split the case and do the job.
2. Reinforced Rear Half Housing — Case Cracked or Scored
On trucks that see real towing or off-road load, the rear half of the case can crack at the output area or get scored badly enough that a bearing kit alone will not seal it. A reinforced rear half replaces that section with a stronger casting built for the abuse, rather than just putting the same weak point back in service.
Typical cost: around $210 for the housing. Labor is similar to a full bearing kit install since the case has to be split either way.
3. Shift Motor — No 4WD Engagement, No Mechanical Noise
The shift motor is the electric actuator that moves the internal range fork when you select 4WD from the dash or floor switch. When it fails, the case usually will not shift at all, or shifts intermittently, with no leak, whine, or rattle to point at. It is a bolt-on external part, so you do not have to split the case to replace it.
Typical cost: around $185 for the motor. DIY install is usually under an hour.
Decision Table
| Symptom | Part Needed | Approx. Cost | Case Must Open? |
|---|---|---|---|
| Fluid leak, general whine | Bearing & Seal Kit | $130-210 | Yes |
| Cracked or scored rear case half | Reinforced Rear Half Housing | ~$210 | Yes (replaces the housing) |
| No 4WD engagement, no noise | Shift Motor | ~$185 | No |
If you are already splitting the case for a bearing and seal job on a truck with heavy towing history, inspect the rear half closely for cracks before you button it back up — it is cheaper to catch that now than to reopen the case later.
Bearing Kits, Rear Halves, and Shift Motors Ship Same-Day
We stock the specific parts for NP261/NP263 jobs like these, matched to the GM applications above. CoreTransmissionParts carries the broader catalog if you need something we don't stock direct.
Shop Gearbox Insider → Shop CoreTransmissionParts →FAQ
Do NP261 and NP263 parts really interchange?
Yes for the case, bearings, and seals — the two differ in the full-time/part-time transfer mechanism, not the case itself. Shift motors and electronic actuators are specific to how your truck's 4WD system is wired, so match those by your truck's build, not just the case code.
How do I know if I need the reinforced rear half instead of just a bearing kit?
If there is a visible crack, a chunk missing, or a scored bore that a new bearing and seal will not seat against cleanly, the housing itself is damaged and a kit will not fix it. A standard bearing and seal job is fine if the case is intact and the problem is just a leak or wear.
Can I replace just the shift motor myself?
Yes — it bolts on from outside the case and does not require splitting anything open. Disconnect the battery before you start since you are working near a wiring harness connector.