Changing Your Transfer Case Fluid

If you own a Jeep Wrangler TJ (not a Rubicon) made in 2004, you have an NP231J model transfer case. The transfer case is a gear box that sits behind the transmission. The transmission serves to transmit power from the engine to the rear driveshaft, but how do you get that power up front for four wheel drive? You have a transfer case.

Essentially, the transfer case sends power out the back to the rear driveshaft, continuing the work of the transmission. It also has a switchable mode where it can engage the front driveshaft and send power forward as well.

The transfer case is the shiny metal gizmo that your rear driveshaft sticks out of. Every 30,000 miles, you should drain the yucky fluid out of it and put in bright, red, shiny new fluid into it. And it isn't hard. If you call around to some Jeep stealerships, you'll find that this fluid change will cost you some $$$. But you can do this yourself for $15.00.

Required Tools

ATF+4 Automatic Transmission Fluid. My 2004 Jeep Wrangler TJ takes this form of fluid. A lot of guys recommend online that you should use any one of a number of synthetic fluids. Nope, not in this vehicle, not yet. How much do you need? 2 quart bottles - about $10.00 worth. The transfer case really won't hold 2 quarts. If I have my Jeep in the driveway nose pointing down the 5 degree decline, I can get 1 4/5 quarts in there. If I have it pointing nose up, I can get 1 1/3 quarts in there. It's full when the red stuff runs out right as you put it in. The Factory Service Manual says to put in 2.2 pints. That's about 1 quart and then just a little bit of the next quart. You can also allow a little more for spillage and the amount that sticks to the inside of the tube adapter, but not much. Don't jack up your jeep in the rear in an attempt to overfill it.

10mm Allen Socket. This little gem is what you need to open the nuts that hold the goo inside the transfer case. Why didn't they just use plugs identical to the oil pan drain plug so the 13mm socket would work here too? Probably because the transfer case is manufactured by a different company that thought up this ingenious and annoying system of plugs. This is the only application I have ever found for my 10mm allen socket.

Oil Drain Pan. You will need your trusty oil drain pan to catch the goo that comes out when you pop the cork.

3/8 inch Ratchet Wrench. My 60 year old standby ratchet wrench by Snap-On pictured here. You will always need one of these if you own a home or a car and ever plan on doing anything approaching useful or handy. Get a good one.

A Pour Spout or Tube. I went to Advance Auto Parts and found this great tube that has a white adapter that screws directly onto the bottle of ATF. It has a valve you can open and close. While using it, I found the tube to be way too long, so I cut it in half and pulled the stopper out of the end and put it on the new end I made. When finished, I had this:

It worked great once I shortened the tube to a reasonable length.

Newspaper. You will not believe how much ATF you spill moving the bottle around, screwing in the tube, draining the case, and refilling it. It gets everywhere. It's really stinky stuff, too. Put down plenty of newspaper. I made a mess and didn't have newspaper out thick enough or over a wide enough area.

Mechanic's Gloves or Work Gloves. Every time I unbolt something on my Jeep, when it finally releases, my hand goes flying into something sharp that gouges a piece out of my hand. Wear gloves and this won't happen to you. It looks like an easy job. But I did it again changing my transfer case fluid. So, wear them always.

Bolt Size & Torque Specifications

Bolt	Size	Torque
T-Case Fill Plug	10mm Allen	15-25 ft-lb
T-Case Drain Plug	10mm Allen	15-25 ft-lb

How to Do it

This is not difficult. It's a little stinky, a lot messy, but really, really easy. It seems like it will be a challenge, but if you can change your air filter, you can do this, too, and you can save some serious coin! And you can take that cash you save, hide it in a piggy bank, and spend it on big tires, new rims, and a lift! YEAH!

1. Put down newspaper under your Jeep from the oil drain plug all the way to the rear differential on the floor at least five pages thick.

2. Place the oil pan. It should be under the back edge of the skid plate and the drain hold in the plate itself. Some directions say to remove the skid plate. Whatever! Just pop the cork and let it go inside the skid plate. Keep a shop towel around to soak up the mess it makes later.

3. Loosen the FILL PLUG. Always check to see if you can get more goo in before you drain the old stuff out. Otherwise, you could end up with an empty transfer case that you cannot fill. How will you drive somewhere to get help? That's right, you'll call a tow truck. LOL! So, always check the fill plug first, and then open the drain plug.

4. Open the drain plug. Splash! Out comes filthy used-to-be-bright-red fluid. And does it ever stink! Let it pour into the drain pan. See how it goes everywhere? That's why the newspaper.

I tried doing this with a funnel under the drain plug. What a disaster! The fluid came out so hard that it filled the funnel and backwashed all over the skid plate anyway, and then it shot out the funnel so hard it went over the pan! Hilarious to some, but I was cussing up a storm. Just let it hit the skid plate.

5. Replace the drain plug. Stick it back in. You can torque it between 15 and 25 ft-lbs. I just screw it back in by hand and then tighten it good with the wrench without pushing too hard.

6. Pour in new ATF+4. Aahhhhh. MY PRECIOUS! Drink and grow big and strong for Daddy! When it starts to leak out of the fill hole, stick the plug back in and tighten it up.

That's it!

Uh oh! I Screwed Up!

My hands stink really bad. Yes, they do, and if you can't smell it, you have a bad cold or smoke too much. Try cutting back on your tobacco consumption or blowing your nose, and use some heavy duty dish detergent or something to scrub your hands. Don't eat finger foods following this job. That's just gross.

My skid plate is covered in crap! Yep. Wipe it down with a towel and throw the towel away. You'll live, and it's not damaged.

My transfer case burned up! Was your Jeep on a hill when you did this, so only a half a qart would go in before it appeared full? That wasn't enough fluid. Also, you are supposed to close up the drain and fill plugs and not leave them on the ground somewhere and drive off.

I can't get all of the ATF out of the bottle like this. No problem. Once you get most out, open the next one, and top it off with what is left, and then pour from it into the t-case.

Where did you get the 10mm allen socket thing? Dude. I can't believe you even asked. It's a Craftsman, of course, and I got it at Sears. If you buy Craftsman, they replace it for free if anything EVER happens to it for you entire life. That's why I don't buy tools at Home Depot or other places. Craftsman is a good tool. Snap-On is another good brand, but the Craftsman guarantee is outstanding and I've used it successfully before.

How far can you drive without fluid in there? If you screw up and spill your fluid, you cannot drive the Jeep without fluid in there. Get a lift from a friend, call a cab to take you to a parts store to buy more, take a bus, ride your bike, or get a tow. DO NOT DRIVE IT WITHOUT FLUID IN THE T-CASE.

What about Mobil 1 or some other Dexcron III Compatible synthetic? The 2004's can't use ATF+3 or compatible. It has to be ATF+4. As of this writing, February 19, 2005, ATF+4 is only available from a Chrysler, Dodge, or Jeep stealership. ATF+4 is not synthetic, but these days supposedly "natural" lubes have so much junk in them, they may as well be synthetics.