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Transfer case model numbers do not map cleanly to a single year or trim. Manufacturers ran two different cases on the exact same model and model year depending on engine, transmission pairing, or a running change mid-year, and the manual-shift and electronic-shift versions of the same basic case (NP231/NP233, NP271/NP273, NP246/NP246C) are often installed across overlapping years on the same truck. Before you order a chain, a bearing kit, or a shift motor, confirm the actual case in front of you — not the one you assume came with that year and model.
Step 1 — Find the ID Tag
Every production transfer case left the factory with a metal ID tag, riveted or bolted directly to the case housing. Location varies by brand and family, but there are three places to check first:
- Side cover or shift-rail housing: the most common spot on New Process and New Venture Gear cases (NP231, NP242, NP246, NP261/263 and their siblings). Often on the driver's side, near where the shift linkage or shift motor attaches.
- Rear output housing: common on Borg-Warner branded cases, near the rear seal and yoke.
- Top of the case, under grime: years of road film, undercoating overspray, or a prior paint job can bury the tag completely. A wire brush and a rag will usually bring the stamped characters back.
The tag carries the model number (for example "231," "4406," or "273"), a date code, and sometimes an assembly or build code specific to the OEM that ordered it.
Step 2 — Read the Naming Convention
The same physical case family is often sold under two naming conventions depending on who branded it. New Process and New Venture Gear (the Chrysler/GM joint venture that later split) use a bare number like "231," "242," or "271." Borg-Warner uses a "BW" prefix followed by a four-digit number, like "BW4406" or "BW4473." Where the two overlap on the same physical case, the common name used in the aftermarket is usually the New Process number — for example, the case badged "BW4406" on some Ford applications is mechanically the same family covered under the NP246 naming elsewhere. When you search for parts, search both the number stamped on your tag and its common cross-reference name, since catalogs are not always consistent about which one they list first.
Step 3 — No Tag, or It's Illegible
Tags get painted over, sandblasted off during a restoration, or simply rust away on an older truck. When that happens, work from what is physically in front of you instead of guessing:
- Casting numbers on the case halves: cast directly into the aluminum, usually on a flat boss near a mounting ear. Not as specific as the tag by itself, but combined with the physical traits below it narrows things down fast.
- Shift mechanism type: a floor lever means a manual-shift case (NP231, NP271, NP241, etc.). A small electric motor with a wiring harness bolted to the side, usually paired with a dash-mounted rotary switch or buttons, means an electronic-shift case (NP233, NP273, NP246, NP261XHD/263XHD, etc.).
- Rear cover bolt count and shape: the number and pattern of bolts on the rear output cover differs between families and is a quick visual check against reference photos once you have narrowed down the likely candidates.
- Input and output spline count: if you are down to two possible models, the input shaft spline count (commonly 23 vs 29 vs 32 depending on family) will usually settle it, though this requires pulling the case or at minimum the front yoke.
Step 4 — Cross-Reference the Build Data
Vehicle-specific build codes narrow things down even when the tag is gone, because they tell you what the vehicle left the factory with, independent of the case itself:
- GM trucks: the RPO code on the Service Parts Identification (SPID) label, usually in the glovebox door or on the driver door jamb, includes a transfer case option code that cross-references directly to a specific model.
- Dodge/Ram and Jeep: the sales code on the factory build sheet (often tucked under a seat or in the glovebox on original-owner trucks) or the door jamb VIN/sales code sticker lists the transfer case option.
- Ford trucks: the door jamb certification label lists axle and drivetrain codes that a parts counter can cross-reference against the case family for that model year.
Build data tells you what left the factory, not necessarily what is on the truck today if the case was ever replaced with a different-generation unit during a prior repair — so treat it as a strong clue, not an absolute answer, and confirm against the physical case whenever possible.
Commonly Confused Pairs
| Pair | How They Differ | What Happens If You Guess Wrong |
|---|---|---|
| NP231 / NP233 | NP231 is lever-shifted; NP233 is electronic-shift with a control module and encoder | Mechanical fork and detent parts ordered for an NP233 will not fit; the real fix was an encoder or module anyway |
| NP246 / NP261XHD / NP263XHD | Different generations and duty ratings sharing a family resemblance; bearing and chain part numbers differ between them | A chain or bearing kit sized for the wrong generation will not seat correctly |
| NP271 / NP273 | NP271 is lever-shifted; NP273 is electronic-shift with a shift motor and encoder | Ordering a shift motor for a lever-shifted NP271 wastes money chasing a part the truck does not have |
| NP231 / NP242 | NP231 is part-time only; NP242 adds a full-time Selec-Trac differential unit | An NP242 overhaul kit is missing parts for the differential; an NP231 kit has parts the 242 does not use |
Still Not Sure Which Case You Have?
Send us the tag numbers, casting numbers, or a few photos of the case before you order. We would rather confirm fitment once than process a return on a chain or seal kit that never had a chance of fitting.
Shop Gearbox Insider → Shop CoreTransmissionParts →FAQ
Can two trucks of the same year and trim have different transfer cases?
Yes. Engine and transmission pairing, a mid-year running change, or a prior repair with a different-generation replacement case can all put a different model under two otherwise identical trucks. Always confirm against the physical case.
What if the tag is painted over and I can't read anything?
Use a wire brush or fine sandpaper on the tag itself, not the surrounding housing, and look at a low angle with a flashlight — stamped characters often still show as a shadow even when paint has filled them in. If that fails, move to casting numbers and physical traits.
Do I need to drop the case to read the tag?
Usually not. Most tags are visible and reachable from underneath the vehicle with the skid plate off, if equipped. Pulling the case is only necessary if you need spline counts or casting numbers that are hidden by the transmission or crossmember.