Cherokee XJ - Project SkyMiles "Phase II"
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By: Berkeley Johnston - 03/2002

Introduction to Phase II of Project SkyMiles, a Cherokee XJ

Project SkyMiles "Phase II" is a combination of upgrades designed to strengthen the Cherokee, make it more versatile, and position the Jeep for future upgrades. The main pillars of Phase II are the addition of a Klune-V 4:1 planetary underdrive (a second transmission) and the switch from a Dana 35c to a Dana 44 rear axle. The upgrade was far from a simple two-step upgrade, however. It was the most complicated project I've yet tackled on my Jeep.



Incredible Ox Locker installed in the Dana 44 rear axle. Klune-V 4:1 planetary underdrive bolted to the NP231DHD 2.72:1 transfer case. Extended t-case hump takes shape. The outlined area is new steel added.
Major components of the Phase II upgrades: A rear Dana 44 axle with Ox Locker and the Klune-V underdrive with new transfer case. Also shown is the modification to the floor pan to make room for the transfer case. The yellow outline shows where new steel was added to the floor.

Phase II Begins

Incrementalism is unavoidable. When I first installed what I now call "Phase I" on my Cherokee... lift, lockers, gears and armor... I thought I would be finished. Perhaps if I never wheeled I would be finished. Or if I never expected as much from my Jeep as I now do, it would have been enough. After reading and wheeling, wheeling and talking, talking and reading, however, I was ready to tackle the next big step of my Jeep build-up. Project SkyMiles Phase II addresses a couple of different issues. The first is the desire for lower gearing. The second issue is the need for a stronger rear axle.

The stock Dana 35c rear axle is not up to the demands I place on it while off-roading. The Dana 35 has the reputation of being weak, and that's true for a few reasons. The axle shafts and gears are small, yes, but more of a problem is the axle housing. The center casting of a Dana 35 is smaller than a Dana 44 casting, and the Dana 35 axle tubes are also smaller. (By measure, my complete Dana 44 axle is over 30% heavier than my Dana 35.) The weaker casting and tubes allow the whole assembly to flex, causing the axles, gears, and even carriers to break more easily. That's just what happened to me one day... so very easily. The right-side axle not only shattered, but it damaged the air seal on the ARB locker as well. The locker still functions, but gear oil leaks into the air lines. I had the proper parts and tools to repair the axle, but the time spent and the potential for similar future breakage had me looking for more strength.

In retrospect, I wish I hadn't spent a dime on the Dana 35 axle. I'll take that expensive lesson and apply it to future upgrade decisions. Ideally, a jeeper should pick a goal and shoot for it. My ultimate goal is a taller lift, long control arms, bigger tires and stronger axles both front and rear. This is still my goal, but I've managed to split this project into Phase II and Phase III without wasting too much money and without throwing away money already spent.

Phase II
Dana 44 rear axle
Klune-V 4:1 Underdrive
SYE short shaft kit (new NP231DHD)
New CV double-cardan driveshafts
Phase III?
Dana 44 high pinion front axle
High steering conversion
6-7" lift (from current 3.5-4")
Long control arms
5x5.5" wheels
33" tires (from current 31")

My expensive 31" Goodyear MT/R tires still have lots of life, so I don't want to go to 33" tires until they're worn down. I want to upgrade to a high pinion Dana 44 front axle with high steering, but the Dana 30 isn't bad... I can live with it. I want to switch to 5x5.5" bolt pattern on the wheels, but I can go to a dual bolt-pattern rear axle and switch later. The front axle conversion is a huge project. I can stick with the small lift and tires, replace just the rear axle (the real problem), add the Klune-V and the new driveshafts. The negative to splitting the project? I might have to modify one or both of the driveshafts when I add more lift and change the front axle.

Which Replacement Axle?

Grinding on the Dana 44 to make room for the Ox Locker.
Grinding on the Dana 44 to make room for the Ox Locker.

I've already told you the punchline... I decided to install a Dana 44 axle. There was a lot of head-scratching involved in that decision, however. Ford 9" or Dana 44? How about an Isuzu 12-bolt? Maybe the Ford 8.8 or even a Dana 60! The Ford 8.8 is a great choice. This stock Ford Explorer axle comes with disc brakes and is just about the correct width. The 8.8 isn't bolt-on, but the conversion is not hard. The Ford 9" axle, especially the Currie high-pinion version, is also attractive... except for the price! An Isuzu 12-bolt axle is another choice. It's stronger than a Dana 44 and comes with disc brakes. The Isuzu 12-bolt, however, is too narrow for my XJ by a lot. Dana 60? If you talk to Dynatrac, they'll convince you that only the Dana 60 is strong enough, but it's too big and heavy for me. (Watch me eat my words in a few years! I hope not.)

In the end I chose a Dana 44. Bart Jacobs wheeled his XJ with a set of Dana 44 axles in the 2001 ARCA and UROC series, using stock (not the stronger alloy) axles and 37" tires! Joe from the SoCalXJ e-mail list had a Dana 44 for sale, so I bought it. It's a great axle, plenty strong, and, because this particular axle originally came from a Cherokee, the exact width and bolt-on easy to install.

Which Locker?

The Ox Locker in pieces... awesome.
The Ox Locker in pieces... awesome.

I was happy with my two ARB lockers. I love the selectability and they never failed to perform. In the back of my mind, however, I always feared a single problem (like a broken compressor) taking out both lockers. Without a source of compressed air, they're worthless. Of course, that's the standard argument you'll get from Detroit locker fans... "They leak!" I could easily have bought another ARB locker for the new Dana 44, but for the sake of being different, I thought I would try something different. I thought about trying a Detroit in the rear, and for a while that was the direction I was headed. The selectability of the ARB, however, was really nice. So when I found out about the recently released Ox Locker, I decided to give it a try. It was expensive and I encountered many problems during the install, but it's finally installed and it works great.

Transfer Case Upgrade

The other weak link in my drivetrain (besides the Dana 35) was the slip-type output of the stock NP231J transfer case. There are lots of ways to eliminate the slip yoke, and few people can agree on what's the best way to do it. There's universal agreement, however, that something should be done! You could do nothing but carry a spare t-case output shaft and drive shaft. Spare parts are usually a good idea anyway. Inexpensive slip yoke eliminator (SYE) kits convert the t-case output to a flange-type, but these use the existing, weak output shaft. More expensive kits completely replace the rear housing of the t-case and upgrade to a larger shaft and a yoke output. The ultimate solution, everyone agrees, is the Atlas II transfer case, but what a price! And there are solutions in between.

I found a deal, the best of all worlds I think, that I couldn't pass up. It's a new, zero-mile heavy duty version of my NP231 transfer case. Originally destined for a full-size Dodge truck, these NP231DHD units are very strong and come with a SYE already installed. There's no core charge, either, so you can sell your old t-case after you swap. JB Conversions is currently selling these new transfer cases for less than you could upgrade all the components of your old case. Take a look at the JB Conversions press release for more details.

Klune-V 4:1 Underdrive

Now here's where the tail started wagging the dog. "Will I get a Klune-V or not?" I said to myself. "If I get a Klune-V now, I won't have to upgrade driveshafts again in the future! And that will save me money!" How deluded I am... I love it!

I figured that if I was going to get a new transfer case and upgrade to a double-cardan (CV) driveshaft in the rear, I might as well go for the brass ring. I love the 2.72:1 low range in my transfer case, but I would also love to have 4:1. How about both? There's plenty of room on a Cherokee for the Klune, especially if the SYE conversion is done.

New double cardan driveshafts from South Bay Driveline.
New double cardan driveshafts from South Bay Driveline.

Driveshafts

One of the benefits of going to a SYE transfer case is that I could then convert the rear driveshaft to a double-cardan style shaft, like the one in front. There are many places to buy new shafts. You can even have existing shafts cut down or lengthened. For various reasons I chose between two widely known and respected shops: Tom Wood's Custom Drive Shafts and South Bay Driveline. For no particular reason (meaning that Tom Wood's would have been just as good), I bought the shafts from Steve at South Bay.

Putting It All Together

I'll be writing lots... lots... of articles to document all the modifications performed during Phase II. There's great information on the way. From John at JB Conversions, there's a treasure of information on the 2.72:1 and 4:1 gear sets used in many NP231-type 4:1 kits and in the Klune-V. From drive shaft experts Tom and Steve, there's information on u-joint and yoke sizes, plus more on CV joints. And there's me trying to weld my floor pan to make room for the Klune-V. The holes got a lot bigger before they were finally welded together!

Until next month!

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