JB Conversions NP231 Heavy Duty Yoke Kit (a.k.a., Slip Yoke Eliminator (SYE) or Short Shaft Conversion)  ($285, Summer 2000):

Tom Wood's Rear CV drive shaft ($290, Summer 2000)

Ease of Installation:	Piece of Cake
Product Usefulness:	Couldn't Live Without It

As I mentioned earlier, once I installed the SYE, I knew I would need a new rear drive shaft.  I didn't bother shopping around; I just called Tom Wood because of his reputation for building very high-quality drive shafts.  Actually, he sells the JB Conversions SYE and one of his top-of-the-line CV drive shafts as a package.  And once you install the SYE, return the old stock transfercase parts for a $75 refund! 

As soon as I had the measurements, I immediately called Tom Wood with the required shaft length (18-3/8"), after which he promised to have the new CV drive shaft in my hands before the weekend. Sure enough, when I got home from work on Friday evening, I had a cylindrical package waiting at my front door. I was REALLY looking forward to getting the rear drive shaft installed. If you’ve ever driven your Jeep in 4WD without a rear drive shaft, you’ll know why. For those of you who haven’t experienced this, it’s a very "jerky" drive, due to the slop in the t-case drive chain. Great, this should be a piece of cake to install! What, are you kidding? Guess what? Even though Tom KNEW what rear axle set-up I had, he didn’t bother to send me the bolts to secure the rear end of the shaft to the rear axle!  I mean, I paid $300 for his "top-of-the-line" drive shaft, and he can’t even supply me with 4 bucks worth of bolts. Then again, maybe Currie should have provided the bolts. I don’t know; it’s just the principle of the thing! On top of that, Tom double charged me for the shaft.  I had to call to remind him that I had already paid in full for both the JB Conversions kit as well as the shaft.  He promptly credited my card for the overcharge, and also reimbursed me for the shipping that JB Conversions charged me to overnight the SYE kit bearing that I was missing.  This was the second time he had complicated my life because of inattention to details!  I'll think twice about doing business with him in the future.

By now it is 5:45 p.m., Tuesday evening.  I rushed over to my local hardware store (still in front wheel drive only), who will be closing in 15 minutes, to purchase four 12mm bolts with 1.75 pitch, 1-inch long. Guess what? They are out of that size! Why am I not surprised? So I purchased some 1½" bolts, took them home, and cut them down to 1-inch. My gawd, what a week!  And my S2K project still isn’t finished!  I still have to hook up my new air lockers.  Fortunately, I can do that at a later date, at my leisure.  At least the Jeep was now mobile, and I could go back to work!

For more information about Tom Wood's line of custom drive shafts, visit his web site at www.4xshaft.com

TeraLow 4-to-1 and JB Conversions Wide Chain Kit ($1050, Jul 2001)

Ease of Installation:	Not Too Bad
Product Usefulness:	Real Glad I Have It

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I was seriously considering an Atlas II transfer case for a while.  But I got a killer deal on the TeraLow and simply couldn't justify spending over twice as much on the Atlas.  Besides, it wouldn't have fit with my flat/belly-up t-case skid plate.  Here's the story on the price.  A guy won a certificate for a TeraLow at the 2001 Chile Challenge in Las Cruces, but he couldn't use it.  I lucked out and was offered the certificate for $800.  I took it!  Add an additional $250 for the wide chain kit from JB Conversions and I now have a pretty stout transfer case! 

As I get more and more mechanically competent with my Jeep, things get easier to do.  Installing this piece of equipment is actually a rather complex project, but since I'd already been inside of my transfer case when I installed the SYE, it didn't seem too bad for me.  For this project, however, I had to remove the whole case from the Jeep, whereas with the SYE install, I did the work without removing the t-case.   Anyway, before I started tearing stuff apart, I wanted to made sure I had everything I needed to complete the project (remember, this is my daily driver).  Although the installation instructions claims that the kit includes a tube of silicone sealer, it doesn't.  So make sure you pick some up before you begin.  I also purchased a can of carb cleaner and 2 quarts of Mobile One synthetic ATF.  And finally, if you don't have a stud remover (I didn't), get yourself a few Grade 8, 3/8" fine-thread nuts.  The installation instructions tell you to "double-nut" the studs to remove and reinstall them, but the factory nuts are too soft--you will strip them--I know this from experience!  :o(  As for special tools, it's very helpful if you have an impact wrench, especially for removing the 1-1/8" front drive shaft yoke nut.  You will also have to remove the front output shaft bearing, which is pressed into the stock front case half, and reinstall it into the TeraLow.  I used an appropriate sized socket and a dead-blow hammer to remove it from the old case.  For reinstallation, I used a 2-1/2" hole saw to cut out a "puck" of wood, which made for a nice, flat, uniform surface for which to whack the bearing into the new case.  Finally, you will also need a torque wrench when putting everything back together.  Of course, I don't consider that a "special" tool.  Everyone who does their own wrenching should already have a good torque wrench.  Other than that, all you will need is the typical assortment of standard and metric wrenches and sockets, a couple of flat screwdrivers, and of course a good pair of snap ring pliers. 

With all of my pieces and parts on hand, I took a half day off of work one Friday so as to get a head start.  After removing the oil pan skid plate, I supported the tranny with a jack stand, and removed the transfer case skid plate.  Next I drained the oil from both the t-case and the tranny, and then removed the front and rear drive shafts.  Before removing the t-case, I had to disconnect the vent hose, shift linkage, 4WD indicator electric harness, and the speedometer gear electric harness.  Next I took up the load of the t-case with my floor jack, removed the six nuts securing the t-case to the tranny, and wiggled the t-case rearward until it was free.  Finally, I lifted the t-case (it weighs about 65 pounds, BTW) onto my newspaper-covered workbench.  This process only took me about an hour and was easier than I expected.  Before calling it a night, I put away all of my tools and cleaned up. Here's a pic of the t-case ready to undergo the conversion.

For those of you who've never seen one, this is a TeraLow.  Basically, it replaces the entire front half of your stock NP231 transfer case.  It already has the 4:1 planetary gears installed, but you have to remove numerous pieces from the front half of your stock t-case and reinstall them into the TeraLow.  The kit also comes with a new front output shaft oil seal, a little tube of Loctite, and a simple set of instructions.  By simple, I mean "of little detail".  I highly recommend that you have your factory service manual close by to assist you with project, especially if you've never been inside of a transfer case!   BTW, if you have snap ring phobia as bad as I do, you will be happy to hear that installation of the TeraLow requires you to remove and reinstall only one snap ring (which holds the front output shaft bearing in place)!  To install the wide chain kit, I had one additional snap ring to deal with.  Speaking of the wide chain kit, the NP231 also comes in a heavy-duty version, which is supposedly used on Dodge full-size trucks.  The wide chain kit includes the beefier chain and associated gears.  I was told that the chain is the weak link in the NP231.  So with over 70,000 miles on my Jeep, I figured this would be a good time to replace it.  The dealer wanted nearly $200 for a new factory chain!  I purchased the wide chain kit from JB Conversions for only $50 more (or $250).  Here's a pic showing the stock and heavy-duty parts.  No other modifications are required to install this kit; just remove the old and replace with the new. 

What the TeraLow installation instructions show, and what you actually see when you pull the stock t-case halves apart, might be different.  In my situation, the main shaft, chain, and front output shaft assembly remained in the rear half of the case.  As a result, some of the steps in the instructions didn't apply.  Therefore, I simply started removing the guts from the stock front case half and started stuffing them into the TeraLow.  The picture to the left shows, clockwise starting with the top left part: 1) the new TeraLow front case half after I swapped all the stuff from the stock case half, 2) the stripped stock front case half, and 3) the stock rear case half with the chain and shafts, which will be reused as is.  The hardest part of this conversion (for me, at least) was removing the 6 studs from the old case and reinstalling them in the TeraLow.  At a price upwards of $1,200, you'd think Tera Manufacturing could have at least installed six bucks worth of studs at their factory!  Oh well.  The instructions recommend "double-nutting" the studs, tightening them against each other, to remove and reinstall the studs.  As I stated in the first paragraph above, don't use the factory nuts!  I striped most of mine and had to replace them.  So I used my wife's minivan to run to the hardware store for 6 new Grade 8 locking nuts, plus a few Grade 8 regular nuts to use to finish transferring the studs to the new case.  The only other real challenge with this project was reinstalling the front output shaft bearing into the TeraLow.  As you can see in the picture, the wooden puck that I cut out with a hole saw fit the bearing race perfectly.  I just had to use care to ensure that the bearing was going in straight.

After applying a bead of RTV sealant, I carefully wiggled the case halves, and everything inside of them, back together.  I was able to check the operation of the shift lever before reinstalling the new t-case back into the Jeep, thus saving myself from a possible headache had anything gone wrong during the rebuild.  Here's a picture of the completed assembly, ready for reinstallation into the Jeep.  Using my floor jack again, I raised the case back into position, mated the splines on the shafts, and wiggled the case snugly against the back of the tranny.  After bolting the t-case back in place, I filled it with new fluid (Tera recommends synthetic, so I used Mobile One); and reconnecting the vent line, shift linkage, and electrical harnesses.  Then I reinstalled the drive shafts and skid plates, and I was finished!  Here's a picture of the converted t-case installed (taken just before I reinstalled the skid plate).  Everything fit back together perfectly. 

       

Note: One concern I had about this product was all the talk I heard about how noisy it is.   In 4 Hi, I can't tell the difference at all from the stock case.  In 4 Lo, however, it's a bit louder, especially at higher RPMs (i.e., over 2,000).  But it really isn't as bad as other's might tell you.  How's it work on the trail? Awesome!  This is one of those things that makes you wonder how you ever got along without up till now!  One thing I've learned after using the TeraLow for awhile now, is that it is hard to get it into 4 Lo while the vehicle is stopped.  But I've had good results by shifting the tranny into neutral, and then shifting the t-case into 4 Lo while the vehicle is moving very slightly (about 1 mph). 

For more information about the TeraLow 4:1 and other related products, visit their web site at www.teraflx.com

                    Copyright 1998 - 2008 Ó by Glenn Bontly