I know it's long, but I'm fairly certain this is the most in depth write up with the most information out there, so bear with me.
I ask that if anything is unclear or I have some bad information in this thread, please let me know kindly and I will be sure to edit it
Why Swap Transfer Cases?
If you're here, you probably have a ZJ with a 249 (full time) transfer case and you are experiencing issues such as hopping around turns, tire screeching, uneven tire wear, and possibly much worse issues. The main cause for these problems? The vicious coupler (a sealed unit with steel clutch plates submersed in a vicious fluid) has reached the end of it's service life (typically 150,000 miles or so). Contrary to popular belief, the 249 is NOT "junk", nor is it a "bad" transfer case. It is actually very durable and it's AWD performance is excellent even with today's standards with a properly working VC.
So why swap if you could just replace the VC? Good question. As you may already know, the VC itself is very expensive. Many don't like the fact they are stuck in 4 wheel drive, and the inability to lock the front and rear axles together in 4 low with the early 249 is a deal breaker for many.
If those things aren't a deal breaker for you, replacing your VC and giving new life to your 249 is a good option, but for most of us, we're more inclined to swap. Here's a quick run down on the three ZJ transfer cases:
NP231: Part time transfer case used commonly in XJ's, YJ's, TJ's, ZJ's, etc. It offers 2wd, 4 part time, and 4 low.
NP242: Full time transfer case used in XJ's and ZJ's. 2wd, 4 part time, 4 full time, and 4 low. The 4 full time feature is unique from the NP249 as it does not use a vicious coupler (what goes bad in the 249), but instead a mechanism that operates similar to an open differential.
NP249: Full time transfer case used exclusively in 93-98 ZJ Grand Cherokees with 4 full time and 4 low. The 249 utilizes a vicious coupler used in conjunction with the center differential found in the 242. This makes for very efficient, and very effective full time operation. 93-95 lack the ability to lock the center differential in 4 low, while a revised version in 96 changed this.
Input Shafts and Gear Cuts
There are 3 different input shafts, .750", .840", and 1.55", as well as both 21 and 23 spline shafts. All ZJ transfer cases have a 23 spline input shaft, and all 92-01 XJ's have a 23 spline input shaft. 91 and older XJ's have the 21 spline input.
Here's a general rule of thumb when determining your input shaft length. This is not always 100% accurate, so make sure you know what you have before buying a transfer case.
93-95 V8 ZJ's: 46RH transmission, 1.55" 23 spline input shaft
93-95 I6 ZJ's with the 42RE: .840" 23 spline input (with collar)
93 I6 ZJ's with the AW4 or AX15: .750" 23 spline input
All 96-98 ZJ's: .840" 23 spline input
All 96-01 XJ's: .840" 23 spline input
92-95 XJ's: .750" 23 spline input
91 and older XJ's: .750" 21 spline input
Here's a good visual for those of you unsure of the different input lengths. From the left, I have a 1.55" input from a 249, a .840" input from a 231, and finally a .750" input from a 242. They are all 23 spline shafts with the old style gear cut and they are all three interchangeable between each case.
A word of caution to those who attempt installing a .750" input in place of a .840" input: If you look closely at the center (.840") input, you'll see the upper most wear ring on the input. This is where the transmission output seal rides on the input shaft. As you can see, it's not very far from the edge of the shaft (approximately 3/10ths of an inch). If you attempt this swap, I recommend sealing the transmission and transfer case surfaces with Ultra Black or Gray RTV. I recommend this if your rig sees any deep mud or water anyways to keep sediment from ruining the transfer case and transmission seals.
When selecting a transfer case, there are many factors to consider. First, the only feasible swap is a 231 or 242 from a JEEP, specifically an XJ or ZJ. Dodge transfer cases will not work, and neither will WJ cases. Dodge cases have a different main shaft and tail cone assembly, and WJ cases have no speedometer sensor provision.
Your best bet is to find a transfer case with the same input shaft. If not, you can swap input shafts, but be aware of the annulus gear cut change that occurred in mid 94. The different gear cuts are easily identified when compared, the late style teeth are much more pointed than the early style and the late style uses a much more narrow bearing.
It's best to go by the build date on the transfer case, not the year of the Jeep when determining the gear pitch. Rule of thumb is cases with a build date of pre 94.5 will have the old style gear cut, and cases with a build date of post 94.5 will have the new style gear cut.
The front bearing width was also changed from a wide (24mm) to a narrow (16mm) bearing along with the new gear cut... Keep that in mind when purchasing a rebuild kit if you're doing a front case swap.
Here's two 1.55" long input shafts. The one on the left is the late gear cut with a 16mm input bearing, and the one on the right is the early gear cut with a 24mm input bearing:
One other issue I've run into: 93-95 ZJ 231 and 242's with the .840 input have a metal collar pressed into the input shaft that mates to the bevel at the end of the transmission output shaft. 96+ transmissions do not have this bevel, meaning it is required to remove the input and either swap it, or you can easily take a deep well socket and tap the collar out along with the main shaft bearing. Reinstall the main shaft bearing into the input, making sure it is fully seated and that is the extent of the fix.
Transfer Case Identification
New Process/New Venture cases utilize very easy to read tags located on the rear case half, just above and to the right of the fill plug. The first three numbers represent the model, with the letter proceeding it indicating the make of the application. An NP242 from a Jeep would simply read "242j".
The correct way to read the date is just how it looks. Month, day, year. So if your case says 8 15 92 1, That would be August 15th, 1992. Most manufacturers aren't this specific on the manufacturing date which would lead you to believe "1" would be January, 1992, however the last number is insignificant.
My personal experience is that a long input 249 with a build date of 7/94 still used the old style gear cut, and a long input 249 with a build date of 1/95 used the new style gear cut.
Front Case Swap
If you're swapping a 242, you can do what is referred to as a front case swap if you're in a bind with two different gear cuts (no pun intended.) The 242 and 249 both share the same front case half, meaning you use all the parts from the 242, with the exception of the 249 input, 249 planetary set, and 249 front case half. You will need to drill an access hole for the mode fork roll pin. This swap would be ideal if you happen to have a late cut 242 and want to swap in an early cut input shaft for example.
While there are several different length drive shafts used though the years, the physical dimensions of the 231, 242, and 249 are very similar. The overall length of each case is within + or - 1/4" of each other, per slip yoke configuration. There are two different slip yoke styles used for the rear drive shaft: Internal and external slip yokes. They are easy to decipher from one another as, well, one has an internal shaft with a tail cone and the other has an external shaft with a dust boot. The external slip yoke is generally found in 96 or newer Jeeps while the internal slip yoke is found in older Jeeps. There is really no huge advantage to either style, however I like how the drive shaft splines are always submerged in ATF in the internal slip yoke case.
The biggest difference between the two is that the external slip yoke case is about 1.5" longer than an ISY case, meaning if you replace your ISY 249 with an ESY 242 for example, you will have to cut and balance your rear drive shaft or have the drive shaft from the donor Jeep on hand.
This is optional. From the factory, the linkage that connects the transfer case to the pivot arm is about 2" shorter on the 231 and 242. If you can easily source the linkage, I recommend it. If not, don't concern yourself with it because you can easily adjust the shifter assembly to make due with the 249 linkage, which we will cover later. You do however NEED the shift tab from the transfer case you are swapping in, the long tab on the 249 will not work.
231/242 Shift Indicator Sensor
The NP249 sensor WILL NOT work in the 231, as the threaded portion is about 3 times longer. I attempted to shim it to no avail. You can however use the 249 sensor in a 242 case. XJ cases do not have the proper provision to have a fully functional VIC, however you can use the 4wd switch on the XJ to show "part time" when in 4wd.
Cheap insurance if you're doing a transfer case swap.
Here's the part numbers for National brand seals from Advance Auto Parts:
NP242/231 rear output seal: 4370N
NP242 front output seal: 3946
NP231 front output seal: 710046
NP242/231 input shaft seal: 3173 (single lip)
NP242/231 input shaft seal: 710928 (dual lip, VERY nice seal!)
46RH, 42RE, 44RE, and 46RE transmission output seal (also known as rear seal): 710058
The new transfer case requires 1.5 quarts of fluid, so grab 2 quarts of any brand/type of ATF. You will need around 2 quarts of ATF +4 to top off the transmission when you are done, depending on how much you lose from the tail of the transmission.
Shift Gates, Shifters, and Bezels
This is a mystery to many that I see brought up often. No modifications need
to be done to the shifter assembly aside from adjusting the linkage. The shifter itself is physically the same no matter what transfer case your ZJ was equipped with, so you can throw one thing out of your head. The plastic shift gates are interchangeable, but once again are not needed. Most people will just toss a matching bezel in their ZJ and call it good, but if you would like to make the swap as factory as possible, all you need to do is swap the plastic shift gate to have predetermined stops when you pull the transfer case shifter.
There are many people who have completed the swap who report difficulty achieving a clean shift into 2wd and 4 low after adjusting the linkage. It is crucial that all of your linkage components are lubricated and in proper working order.
The absolute most common issue I've seen is the torque shaft bearing on the body side mount. The torque shaft is the part of the shifter linkage that pivots, and connects from a rubber bushing in a bracket on the transmission to a metal "bearing" (or bushing) on the body mount. The bearing is notorious for coming out of it's oval shaped metal retaining plate and sliding back and forth on the torque shaft, and believe it or not, this alone can reduce the shifter throw up to a full inch in either direction. In this picture, you can see the bearing has separated from it's retainer and is sitting loosely on the torque shaft:
A revised part designed to prevent this failure is available here: http://www.quadratec.com/products/52207_0007.htm
, Or from your local dealership.
Slip Yoke Eliminators (SYE's)
My general advice when swapping transfer cases it to keep the current and future usage in mind. If you're already up 4.5" or higher (or have serious plans to go that high in the future), consider adding a SYE to your swap.
There are two types of SYE's: A real SYE that replaces the main shaft with a heavy duty unit, and what is known as a hack and tap that involves installing a yoke on the end of the stock main shaft.
I don't recommend the hack and tap method. The weakest point of both the 231 and 242 is where the main shaft steps down at the speedometer worm gear. They are notorious for shearing in this area. A real SYE with a HD main shaft eliminates this weak point, whereas a hack and tap does nothing to address it.
Sadly, if you have a 242 a hack and tap is your only off the shelf option for a SYE which is why if you need a SYE, you should skip a 242 and go straight for a 231.
As far as the brand goes, there are tons of SYE's out there. I have had excellent success with the Rugged Ridge HD SYE kit, as well as the JB Conversions kit. I have not run across any particular kit that I would recommend staying away from, however I would put JB conversions and the AA kit slightly above the Rugged Ridge/Crown kit.
-14mm or 9/16" open end wrenches (a 9/16" ratchet wrench is GREAT!)
-Metric socket set with ratchets (8-18mm, deep wells may be needed)
-Channel locks and pliers
-Air tools (optional)
Required If Swapping Inputs
All of the aforementioned tools are required with the addition of a good set of lock ring pliers, large pipe wrench, 1 1/8" socket, a 1/2" drive breaker bar, and a foot/pounds torque wrench. You will also need a tube of Ultra Black RTV.
*Skip if you do not need to swap inputs*
1. Remove the (4) 10mm bolts from the front bearing retainer located around the input shaft.
2. After scraping off the excess RTV, you will see two lock rings: One holding the input bearing in place, and the other holding the input shaft into the bearing. You only need to remove the smaller lock ring if you are not using the bearing from the 249 case.
3. Remove the front output yoke from the transfer case. To do this, put the case on the concrete and support it with blocks. Then, place a large pipe wrench or cresent wrench on the yoke, and apply pressure to the retaining nut with a 1 1/8" socket and 1/2" drive breaker bar. Of course if you have an impact, you can just run the nut out pretty easily.
4. Remove the (10) 15mm bolts holding the case together, and the (1) 12 point 10mm bolt.
5. If you look closely, there will be one indentation on each side of the case where you can stick a flat head screwdriver in to pry the case halves apart.
Once you have the case apart, throw the rear half to the side. You will not need anything from it with the exception of the speedometer sensor for your new 231 or 242.
6. Turn your attention to the front half: The 249 has a simple shift mode fork that just pulls straight up out of the case after removing the shift detent spring located on the bottom of the case using a 7/8" wrench. Now you can remove the input shaft and it's planetary gear set. It may take a little tapping on the input shaft to remove it. Use a flat head screwdriver to remove the planetary lock ring, and remove the input from the planetary assembly.
You can either use the entire planetary set and input from the 249 (what I opted to do) or you can use the 249 input in the 242 planetary. Make SURE that the gear cuts match, they will drop into the other's annulus gear however it won't last long that way.
I recommend giving the donor a good bath before you open it up. The less grime falling into the case the better.
The 242/231 disassembles much like the 249. Remove the bearing retainer on the front of the case, remove the input shaft lock ring, remove the front output yoke, remove the 10 15mm bolts and the 1 12 point 10mm bolt, and finally pry the case apart.
The 242 looks much like the 249 inside. However, it has a larger, more complicated shift assembly due to the different gear positions.
The mode fork is two pieces in the 242 and 231: Mode fork and low range fork. Remove the mode shift sleeve from the top assembly as well as the plastic pads on the fork.
*231 may be slightly different, the following description is for a 242*
Start by pulling the shift rail (long rod holding the fork assemblies together) straight out of the case. To do this, you will need to remove the rubber plug from the outside of the case and get a left hand drill bit to remove the pin, or a #1 screw extractor.
Remove the shift detent spring assembly from the bottom of the case using a 7/8" wrench
Then, remove the mode fork, followed by the low range fork.
Now you can remove the input and planetary set.
If you want to avoid removing the roll pin from the shift rail, you can pry the pin holding the mode fork into the shift sector away from the shift sector and pull the mode fork up and out. It takes a little prying, but it works. Removing the roll pin is a much better solution, however I have run into some stubborn roll pins before.
I recommend bathing the front half of the case in solvent to get rid of any grime that's present, then cleaning it well with brake cleaner and compressed air. Be careful with the input bearing and front output bearing. Either remove them before cleaning the case, or be sure to clean them very well with brake cleaner and compressed air afterwards. You will also need to remove the old seals at this time.
After you have the front half of the case clean and dry, as well as the 249 input shaft and planetary set, drop the assembly into the case, with liberal amounts of ATF to lube the gears.
Flip the case over and install the lock ring to keep the assembly from falling out.
242 front case with 249 long input installed:
After installing the snap ring, replace the front bearing retainer using a thin bead of Ultra Black RTV. Be sure to align the oil gallery hole up with the indentation in the cover, and torque the bolts to 16 ft. lbs. Now is a good time to install the new input seal as well.
Flip the case over again and install the low range fork into the case with the fork hub facing down into the planetary set. Be sure to lube everything with some ATF.
Then install the mode fork with the mode sleeve facing upright.
Slide the shift rail through the fork assemblies until it fully engages into the provision in the case.
Clean the magnet and place it back into the provision in the case. I like to use a little grease or petroleum jelly to keep the magnet from falling out upon reassembly.
Moving onto the back section of the case, visually inspect all the components for any stress cracks or abnormal wear. Also inspect the chain for any stretching.
Remove the old RTV from the back section of the case. A thin wire brush works well here as it's easy to score the aluminum with anything else.
Clean the case, gears, and chain with brake clean and compressed air. Make sure the oil pump pickup is clean from any debris.
Set the two case halves on the bench. Place a thin bead of Ultra Black RTV around one of the mating surfaces.
Put some assembly lube on the intermediate shaft splines, as well as any other mating/bearing surfaces.
Push the two case halves together, aligning the shift rail as well as the mode sleeves and the intermediate shaft.
The case should "pop" together with little effort. Once it's together, spin the input shaft and cycle the case through all the gears. If all is well, install all of the case bolts (the two holes with dowel pins use the longer bolts as well as washers, this is IMPORTANT!)
Torque the case bolts to 30 ft. lbs.
Install the new rear output seal and the front output seal. Install the front output yoke and torque the retaining nut to 110 ft. lbs.
The case is ready to go into your Jeep.
Transfer Case Removal and Installation
Start by either driving your Jeep onto a set of ramps or jacking it up and placing jack stands under your Heep. Be sure to chock your wheels, and PLEASE, PLEASE don't rely on a jack to support the Jeep. You will need it later anyways.
Drain the old T case (this is where the 30mm socket comes in handy, and be sure to recycle your old fluid!)
Check again that your wheels are chocked, and put the transfer case in neutral. Remove the front and rear drive shafts using an 8mm socket or ratchet wrench.
Remove the shift linkage from the Tcase, along with the speed sensor and shift indicator connectors.
Remove the shift linkage from the transmission by placing a pry bar between the linkage and the mount.
Place your jack under the middle of the transmission cross member. Put a little pressure on it, and remove the 4 15mm cross member bolts.
lower the transmission and transfer case, watch for binding or pulling of any electrical or mechanical connections, then remove the transfer case vent from the clips on the transmission.
Once you feel you can access the top nuts on the transfer case, remove the bottom 4 with the 14mm or 9/16" wrench. Loosen the 2 top nuts, but leave them started until you are completely ready to remove the case. A buddy is nice here, however the case is not too heavy and should be handled easily by one person (no problem for me, but I bench 240 so... haha)
Finish removing the top 2 nuts, and slowly pull the transfer case from the transmission. Be sure to place a pan under the tail of the transmission first as you will lose a bit of fluid.
Now that you have the 249 out, you can put a new output seal on the transmission, and hopefully by now you have your 231/242 ready to go with new seals. Swap the speed sensor and gear from the 249 into your 231, paying attention to it's position in the 249 case.
As Haynes would say, installation is reverse of removal. Be sure to fill with new fluid once it is installed!!!
Once you have the new case back in, it's time to decide if you need to adjust the transfer case linkage. Try and engage 4 lo. If you have an easy, full swing of each gear, then no adjustment is necessary. Most likely though, you will not be able to fully engage 4 lo. This is easily fixed. Put the shift lever in 2wd, then get under the Jeep and loosen the 13mm adjustment bolt on the shift linkage. Push the shifter all the way forward, and tighten the adjustment bolt. You should have full engagement of all gears now. If you have the new shifter gate or shift bezel, now is the time to install it. Take it for a test drive and be sure to test all the gears, then take it back to the shop and check for leaks. Check the fluid one more time, and correct any leaks that may be present.
For the lights in the VIC (Vehicle Information Center) to function properly with the new transfer case, it's as simple as a plug.
For connecting a two prong switch to a four prong connector, refer to this link:
Start by removing the 4 screws holding the console bezel in place
Remove the 2 lights from the cigarette lighter and ash tray, and the power to the cigarette lighter.
Remove the three screws holding the VIC in place (two on top, 1 on the bottom) and slide straight out.
If you had the NP249, the red plugs should be connected:
Disconnect the red plugs, and dig in the wire loom until you find 2 black plugs. 1 female and 1 male, then connect them together.
The plugs should look like this:
Leave the red plugs un plugged, just as the black ones were, and again, installation is reverse of removal.