Dana 300
Donor Vehicles: '80-'86 Jeep CJs
Swap into: Any universal series Jeep that is getting a passenger drop front axle, any '79 and earlier Jeep that is getting a different transmission, or any lightweight full-size or full-size with an anemic power plant.
Identify: A cast-iron case with an aluminum rear output housing, aluminum shift rail/shifter mount casting, common round 6-bolt mounting arrangement, a centered rear output, and an inspection cover on the bottom.
Pros: A lower low range than its predecessors, while still having a cast-iron case and direct gear-driven architecture, it also has the more modern 23-spline/6-bolt round attachment and input which facilitates installation with many modern transmissions. Many consider this the pinnacle of Jeep transfer cases.
Cons: Leaks from the shift rails are not uncommon, stock clocking is almost 25-degrees down from flat, and the stock single stick shifter can become stuck and balky with remarkable ease.
Comments: A swap to a twin stick setup can solve the balkiness issue, and a clocking/adapter ring from either Advance Adapters or Novak Conversions can allow you to clock the case flat or bolt it to an AX-15 or other YJ/TJ transmission, while a flip-kit or Stak 4x4's complete aluminum replacement case can allow it to run with a driver's side drop front axle. There is no shortage of aftermarket support including heavy duty outputs, 4:1 gear kits, twin-stick shifters and even complete aftermarket rebuilt units.
New Process NP231
Donor Vehicles: '88-'06 Wrangler '88-'01 XJ/MJ, some ZJs with the inline-six, and '88-'96 Dodge Dakotas and Rams
Swap into: Any '87 XJ/MJ or YJ to replace the NP207, Grand Cherokees with a full-time 4WD case, or any Jeep that came with an NP242
Identify: The easiest way is by looking at the aluminum and red tag next to the rear output above the fill plug. Look for the numbers "231J" at the top of the tag. Beyond that, if there are four detents in the shift lever, or if the donor's 4WD indicator has 2WD, 4HI, N, 4LO it could be an NP231.
Pros: Shift-on-the-fly capability, the largest aftermarket support of any factory transfer case including lower low range kits, heavy-duty outputs, heavy-duty chains, two-wheel drive low kits and more.
Cons: The aluminum case is relatively fragile, and the chain and detents for four-wheel-drive ranges can slip.
Comments: A lot of old-school Jeepers look down their noses at this case, but the fact of the matter is it is easier to live with and the internals are as strong as the Dana 300. It got a reputation for not being as strong thanks to guys with no skid plates whacking the relatively thin aluminum case off of rocks, or guys with no concept of chain maintenance busting chains. Make sure your chain is in good shape, make sure it is full of the correct fluid, keep the thing off the rocks, and this could be the most trouble-free T-case you ever use.
New Venture Gear NVG241OR
Donor Vehicles: '03-'06 Wrangler Rubicon
Swap into: Any Jeep equipped with a driver's side drop front axle and a transmission with a common round 6-bolt pattern and 23-spline output.
Identify: Like the NP231, look for the tag near the rear output above the fill plug. The case itself looks a lot like an NP231, but it has a balancer on the output requiring a flanged driveshaft, more bolts holding the case halves together and a larger nose area where the input is (which houses the planetary low range).
Pros: With a bigger chain, more bolts holding it together, and a larger planetary set, this is a much beefier T-case than the NP231.
Cons: Its size can be a detriment to clocking it flat, and not everyone needs the 4:1 gears.
Comments: Only available in the Rubicon Jeeps to date, the JK NP241 won't easily swap into the earlier TJ/YJ/XJ/MJ/ZJ Jeeps. The TJ cases though will bolt up in most applications with minimal fuss. The stock shifter linkage will likely have enough adjustment to work too. The front driveshaft should be able to be kept, but the rear will need modifications. There is no mechanical speedometer output so earlier Jeeps will need another solution for speed pickup.