I have heard that a Cherokee Selec-Trac NP242 transfer case will swap onto a Grand Cherokee ZJ with a V-8. I would like to know what is involved if it’s true. It would be nice to drive around in two-wheel drive.
What you have heard is correct. The NP242 transfer case is a great option for Grand Cherokee owners who have an NP247 or NP249. Though there’s nothing wrong with the latter full-time transfer cases, repairing the viscous coupling in the T-case when it wears out can get expensive, and some of the very early units did not have a true 50/50 torque split when in low-range. The NP242 offers 2-Hi, full-time Hi, part-time Hi, Neutral, and 4-Lo, whereas the other cases have no 2-Hi selection. The full-time selection of an NP242 is simpler than the other cases and uses a mechanism similar to an open differential rather than a viscous coupling. The 2WD option of the NP242 does offer a slight mileage improvement, and it also enables smoky burnouts with V-8 Grands.
We have covered this swap before in these pages and so has our sister publication, Jp magazine, a couple of times. Search our supersite, fourwheeler.com, to find these articles, one of which is at this link, though the subject was a later WJ.
As for what you will need, the first step is to acquire an NP242 from an XJ Cherokee, ZJ Grand Cherokee, or MJ Comanche. They were used sporadically starting in 1987 depending on how these vehicles were optioned out, but they were never offered behind ZJs with a V-8. It should be noted that the NP242 was also used in select Dodge applications, but none of these are viable swap candidates. They are relatively plentiful in junkyards, and for this reason we recommend trying to find one close to the same year as your Grand. Why? It’s more likely to have the correct speedometer drive gear provisions that you’ll need as well as the correct driveshaft configurations.
Although they were pretty consistent throughout their production run, there are a couple of key differences you’ll need to pay attention to. The most important is the front input gear; while they are almost all 23-spline, the input gear length can vary, and it’s likely going to be different than your V-8 Grand. This isn’t a big deal, however, because you can swap the input gear from your existing NP249 into the NP242. They interchange, but be aware that there may be a difference in the input bearing width that you’ll need to address. The procedure requires complete disassembly of both transfer cases to do the swap, but the process isn’t that hard as long as you have a good pair of snap ring pliers. There were a couple of different rear driveshaft arrangements used, so take note of what you have and select a donor that matches. The external dimensions of the cases are very similar, so more than likely you won’t need to do any driveshaft modifications if you get the right donor. All of the sensors should bolt right up, and even the existing transfer case shift linkage you have can be adjusted to work with the NP242 if you shorten the shift lever arm on the T-case. For good measure, you can also swap the shift mechanism and bezel from a NP242-equipped ZJ for a correctly labeled range selection and a completely stock-looking swap once you’re done.
Back to driveshafts. Since you will already be elbow-deep into the transfer case, you might consider installing a slip-yoke eliminator kit. There are hack-and-tap kits out there, but Tom Wood’s Custom Drive Shafts (customdriveshafts.com) offers a very strong kit that includes a bigger output shaft and has provisions for a rear driveshaft with a CV. Though more of an investment, an SYE kit is a great choice if you’re running a lift kit over 4 inches or tend to be hard on your Jeep. You can check out an installation article on the kit here.