When the time came to transform our 2WD ’91 Comanche Sh!%box Derby into a full-fledged 4WD Jeep, we knew we didn’t want to spend a ton of money doing it. And since the truck was running and driving, we weren’t in a big hurry to pull it apart. So we took our time and over the course of a year we scrounged through junkyards to come up with as many used parts as we could to make it happen.
We pulled the AX-15 transmission...
We pulled the AX-15 transmission and NP231 T-case out of a ’91 Cherokee that had very low mileage. While the T-case had the ’91-only speedometer sending unit, the input shaft of the transmission told us that the tranny was swapped into the Cherokee from a later-year Jeep.
The Comanche is a relatively rare Jeep and the 4WD Comanche is even more so, but we were confident we’d be able to find most, if not all, of the parts we’d need by crawling in the dirt under pre-used Jeeps. The Comanche shares almost everything with the Cherokee from about the middle of the driver’s door forward, and knowing that fact opened up a ton of options. In the end we were able to pillage a transmission and T-case, front driveshaft, T-case shift linkage, and console insert out of donor Cherokees. Because we had time we were more selective with what we pulled and only grabbed the best parts, so we were able to do the swap without rebuilding or even resealing the tranny or T-case.
We have no problem at all buying a 2WD XJ or MJ because we know that it is possible to convert them easily and cheaply to 4WD. It’s a complete bolt-in swap. And, in the case of MJs, we find the 2WD ones to be straighter with less Unitbody fatigue. We’ve done this quite a few times now and we’ve picked up some tricks along the way. So if you are saddled with a 2WD XJ or MJ, or you are thinking of buying one, we say go for it and then follow these tips to easily make it the Jeep it should be.
If you have a choice, grab...
If you have a choice, grab the later ’93½-up external slave version of the transmission and bellhousing (right). It is much more reliable than the early setup. In a year we had only found one such setup and when we got it off the Jeep, the bellhousing was cracked. We were working with Advance Adapters on another story and saw a stack of used AX-15 bellhousings sitting at the shop. The company has both new and used bellhousings as well as all the other parts you need to upgrade to hydraulic clutch linkage. To swap from an internal slave to an external, you need to nab a bellhousing, a slave cylinder, an input bearing retainer, a clutch fork, and a hydraulic line.
Here you can see a ’93½-up...
Here you can see a ’93½-up input shaft bushing against a ’93½-down input shaft. When Jeep changed over from the internal hydraulic throwout bearing to the external slave/master hydraulic setup the tip of the input shaft went from the early 0.590-inch to the later 0.750-inch diameter. We knew the year of the Cherokee the tranny came out of and it still had the hydraulic throwout bearing, but it had the wrong diameter input shaft tip.
This truck had a hard life...
This truck had a hard life and with only 140,000 miles on the odometer the input bearing had turned to dust. Since we ended up with a larger input shaft tip, we had to swap it out anyway. We used Advanced Adapter’s oil-impregnated bronze input bushing and soaked it in motor oil overnight before installing it. This much-larger-than-stock bushing sits further out on the crank so it contacts a fresh and smooth section of the input which helps keep clutch chatter at bay.
When you pull the transmission...
When you pull the transmission and T-case from your donor make sure to get all of the factory T-case shifter brackets. There is the shifter itself which mounts to the floor from inside, there is a body-side pivot that mounts through the floor under the Jeep, and there is a T-case mounted pivot that picks up two of the T-case bolts. Grab all three as well as the two shift rods and the indicator that will snap right into your factory console.
In these Jeeps, the shifter...
In these Jeeps, the shifter and body-side pivot are both bolted through the sheetmetal under the carpet. When we are in the junkyard, we have no problem just cutting carpet to take out the shifter and pivot plates. However, on our own Jeeps, we’ve found it is easier just to pull the front seat or seats and carpet to install the parts. The shifter bolt holes are pre-existing and the shifter hole is covered with a block-off plate. The body-side mount holes are not pre-drilled, however the floor board is stamped to show you where to drill.
At 6½ inches of lift we knew...
At 6½ inches of lift we knew we were going to need a slip-yoke-eliminator. So, we picked up regular-length kit from JB Conversions for just $199. With the distance the Comanche has between the rear axle and the T-case there is no need for a super-short kit. Plus, the ’91-only speedometer sender and speedometer won’t work with the sensor and tone ring in the super-short kits. We opted for a 1350 U-joint yoke at both the T-case and rear axle and went with a Tom Wood’s driveshaft to connect the two. The junkyard front driveshaft worked great. Just make sure you grab the driveshaft from an XJ or MJ with the same transmission and T-case you are using to avoid any length problems.
If you are working with a...
If you are working with a ’91-up Jeep, you will need to lengthen the speedometer wire approximately 18 inches. If you are working with a ’90-earlier Jeep, you will want to grab the speedometer cable out of whatever you nab the transmission and T-case out of. We didn’t bother hooking up the dashboard 4x4 light. We know when we are in 4WD just fine without it.
Our factory transmission mount...
Our factory transmission mount was hashed, but we didn’t know it until we got into the swap. Had we known we’d have looked for a good one in the junkyard. That is, we would have before we found out that a brand new mount could be had from Rock Auto for just $11.52. We are cheap, but we aren’t cheap enough that an $11 savings is worth swapping mounts when the junkyard mount pops. Check Rock Auto out for parts before just grabbing whatever used junk at the junkyard. You might be pleasantly surprised, as we were.
Once we had everything bolted...
Once we had everything bolted up, we put Amsoil Severe Gear 75W-90 in the transmission and Multi-Vehicle ATF in the T-case. While we didn’t rebuild either box, they both shift smoothly and filling them with Amsoil will help guarantee that they do so for a long time.
Make sure that whatever front...
Make sure that whatever front axle you toss in the Jeep has the same gears as the rear axle does. This front Dana 30 came out of a ’99 Cherokee so it had the bigger 760X-sized U-joints, no CAD, and it already had the truss and Crane differential cover. However, it was still running an open carrier and the gears were too high for our application. So, we went to 4WD hardware for an Eaton Detroit Truetrac, 4.56 G2 gears, and a setup kit. We had Jim Cox at American Overland Expedition set the gears up for us, and since Trasborg is a mud-hound, the Superior Axle outer axle seals will keep the mud from killing the inner axle seals.
Out back we went with simple....
Out back we went with simple. Thanks to driving the Lincoln-locked Dana 44 daily for six months, we knew we were OK with the way the truck handled, but there was always the nagging thought in the back of our heads about the welds giving up. So, Jim at AOE put a G2 spool in it along with a set of 4.56 gears and topped it off with a Crane differential cover to match the bulletproof cover on the front axle.
Pinion depth is a rough thing...
Pinion depth is a rough thing to dead-reckon, but that is the way we were taught to set up gears. Jim at AOE has been doing gear setups for a long time and uses this pinion-depth tool to quickly and easily figure out how many shims to add or remove to get it to the nominal depth. In this case, a Dana 44 should have a nominal depth of 2.625 inches and we were 0.015 off. Jim put in the correct shims and had both axles setup and dead-on in about a half-day’s worth of work.