ZJ 249-231 Swap FAQ Write-Up
So you’re sick of that POS 249 and want a real t-case? Here’s how to do it. First, I’ll run through some of the reasons why people swap in a 231. Low-Lock The 93-95 249’s still rely on the viscous coupler to transfer power while in 4Lo. This presents a major problem off road as the front and rear driveshafts are NOT locked together. This issue is most apparent when attempting to climb a steep obstacle. With the weight off of the front tires, a majority of the power is sent to the front because they are easier to turn, but with no weight on the tires, you get no traction up front! ] Viscous Coupler Failures The Viscous Coupler in all 249’s is prone to failing around the 75,000 mile mark. An easy test for the VC is to do several figure 8 maneuvers in a parking lot after driving the Jeep for 30 minutes or so at highway speeds. If the vehicle can idle through the maneuver, chances are the VC is okay. If it binds or needs additional power, your VC is likely on its way out. A VC from the stealer-ship will run you about $800, so it is usually MUCH cheaper to swap in a 231 or 242. [/et_pb_text][et_pb_text _builder_version="3.0.52" background_layout="light" text_orientation="left" border_style="solid"] SYE At extreme lift heights, the rear driveshaft can cause vibrations. Currently there is no slip-yoke eliminator for the 249, and probably will never be one. An SYE creates a fixed rear output shaft on the t-case, much like the front output. This strengthens the rear output, as well as lengthens the rear driveshaft, lessening the angles on the joints, which can usually eliminate the vibrations. [/et_pb_text][et_pb_text _builder_version="3.0.52" background_layout="light" text_orientation="left" border_style="solid"]
Now, onto the swap itself:
Where to get your 231: Most 231’s will work, but may not necessarily bolt in. Ideally you will find one with a 23 spline input shaft that matches the length of your current input shaft. There’s no for sure way that I know of to determine the length of your input shaft without pulling the t-case and measuring it. You can find 231’s in YJ’s, XJs, and TJs, but they are pretty rare to come stock in ZJs. On the YJ’s, they use a different front output yoke that will not work with your driveshaft. You can find the proper output yoke at most tranny shops. Try to get a t-case out of a vehicle the same year as yours, or at least close to it. [/et_pb_text][et_pb_text _builder_version="3.0.52" background_layout="light" text_orientation="left" border_style="solid"] So now I have my 231, what do I do with it? Start by taking out your old 249. I find it easiest to drive the ZJ up onto 4 ramps when doing t-case work, or putting it on a lift. Be sure you are in 4WD if you pull up onto the plastic ramps though. It’s very hard to push the front tires up onto the ramps and you don’t want to shoot the ramps out from under the rear tires. Don’t ask how I know this! It helps to have some people helping, as the t-case is pretty heavy and not fun to maneuver by yourself. So raise the vehicle and secure it in place with the e-brake (putting it in park will obviously not work as you are removing the drivetrain!) and other methods if you so desire.- remove front and rear driveshafts (fluid will probably leak out the rear output when your pull the rear shaft, so you may want a drip pan)
- place a jack under the tranny pan using a block of wood or some other method to keep from damaging the pan.
- Disconnect all hoses, linkage, and other fittings on the t-case
- Drain the fluid of the 249 (30mm socket or wrench to open drain plug)
- Remove the 4 bolts holding the crossmember to the frame rails (be sure your jack is holding up the tranny and t-case or things will get very bad VERY quickly)
- SLOWLY lower the jack under the tranny pan until you can access all 6 nuts holding the t-case to the tranny. These should be 9/16” or their metric equivalent. They are a MAJOR PITA to get to, so be patient. Leave a couple bolts on the mounting studs to hold the t-case on until you’re ready to yank it. Raise the jack back up once you have the upper bolts removed
- Using a tranny jack or pure muscle, now remove the t-case from the tranny. You will need to slide the t-case back, and then it will come down. Tranny fluid will probably leak out a little bit, so again a drip pan is a good idea.