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The NP242 is New Process's full-time transfer case, best known as the unit behind Jeep's Selec-Trac and Quadra-Trac systems on the Grand Cherokee ZJ and WJ, with the same case also showing up on some Cherokee XJ and Wrangler applications and Dodge 4WD trucks that shared the drivetrain. What sets it apart from the simpler NP231 and NP241 is a center differential: instead of only offering 2WD, 4-High, and 4-Low like a part-time case, the NP242 adds a true Full Time 4WD mode that can run on dry pavement without binding the front and rear axles together.
That extra mode means an extra set of parts to wear out. Under the shift fork and the usual chain-and-sprocket drive, the NP242 carries a center differential with its own clutch pack that lets the front and rear outputs spin at slightly different speeds in Full Time mode. Everything else — the chain, the pump, the output seals — wears the same way it does on any New Process case of this era.
Common Failure Modes
Chain Stretch — Worse in Full Time Than Part Time
The drive chain between the mainshaft and front output sprocket stretches with mileage like any roller chain. The tell on a 242 specifically is that the noise is often worse in Full Time mode and quieter in Part Time, because Full Time loads the drivetrain continuously instead of only when 4WD is engaged. A replacement drive chain is the fix once you have ruled out the center differential as the noise source.
Center Differential Clutch Wear
The clutch pack inside the center differential is what lets the NP242 run in Full Time 4WD without binding up on dry pavement. Worn clutch plates produce a growl or howl that shows up specifically in Full Time and disappears or changes character when you shift to Part Time, because Part Time locks the front and rear outputs together mechanically instead of relying on the clutch pack to manage the speed difference.
Output Seal Leaks
Front and rear output shaft seals harden and leak with age, same as any transfer case. On a Grand Cherokee this usually shows up as a fluid spot under the front or rear of the case, and because the NP242 bolts to the back of the automatic transmission, a rear leak is often mistaken for a transmission pan or tailhousing leak until someone traces it back to the transfer case.
Shift Motor Issues on Electronic Applications
Some Grand Cherokee applications pair an electronic shift motor with the mode selector instead of a simple mechanical lever. When that motor or its wiring fails, the dash indicator behaves erratically or the case will not respond to a mode change at all, even though the chain, pump, and center diff are perfectly healthy. Confirm which shift mechanism your application actually uses before assuming a mechanical failure.
The Symptom Everyone Searches
Growls or howls only in Full Time: start with the center differential clutch pack, not the rear output bearing. Shift to Part Time and see if the noise changes character or disappears — if it does, the clutch pack or the chain is the likely source, not a bearing that would growl in every mode.
Won't engage Full Time or Part Time at all: check the shift motor and linkage first on electronic-shift applications, then the shift fork and detent on mechanical-lever applications, before assuming the case itself has failed internally.
Repair Cost — DIY vs Shop
| Failure Mode | Symptom | Typical Fix | Rough Cost |
|---|---|---|---|
| Stretched chain | Growl/howl worse in Full Time | Replace drive chain, full teardown required | $100-180 parts DIY / $600-950 shop |
| Worn center diff clutches | Growl/howl specific to Full Time mode | Replace clutch pack during teardown | $120-220 parts DIY / $650-1,000 shop |
| Output seal leak | Fluid spot under case | Replace front or rear output seal | $20-40 parts DIY / $150-250 shop |
| Worn case bearings | Growl present in every mode | Full bearing and seal overhaul | $150-280 parts DIY / $650-1,000 shop |
| Full internal failure | Grinding, no 4WD engagement, metal in fluid | Full rebuild or reman/used replacement installed | $900-1,400 shop replacement |
NP242 vs NP231 — Know Which One You Have
These two New Process cases share a family resemblance but are not the same part. The NP231 is part-time only, giving you 2WD, 4-High, Neutral, and 4-Low, and is what sits behind most Wrangler YJ/TJ and Cherokee XJ drivetrains. The NP242 adds the center differential described above for true Full Time 4WD and is the case Jeep paired with Selec-Trac and Quadra-Trac on the Grand Cherokee. If your Jeep has a Full Time 4WD setting on the transfer case selector that does not bind the axles on dry pavement, you have a 242, not a 231, and the parts are not interchangeable between them.
Parts Ship Same-Day
Drive chains and the rest of the drivetrain parts behind your Grand Cherokee, in stock and ready to ship before 2pm Eastern. CoreTransmissionParts carries the broader catalog if you need something we don't stock direct.
Shop Gearbox Insider → Shop CoreTransmissionParts →FAQ
Why does my NP242 only growl in Full Time 4WD?
The center differential and its clutch pack only work in Full Time mode. A growl or howl that is present in Full Time and quiet in Part Time points at the center diff clutches or the chain and sprockets wearing, not at the rear output bearing.
Will a chain replacement fix a leaking NP242?
No. A stretched chain causes noise and driveline slop, not leaks. An output seal leak is a separate failure and needs its own seal, though if the case is already apart for a chain it is the right time to replace the seals too.
Is the NP242 the same case as the NP231?
No. They share a family resemblance and some fasteners, but the NP231 is part-time only (2WD, 4-High, 4-Low), while the NP242 adds a center differential for true Full Time 4WD on dry pavement. The 242 is the more complex case and the one you find on Grand Cherokee, not the Wrangler's base transfer case.