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Based on the condition of the rest of our fluids, we figured the ATF in the transfer case was probably original, or at the very least many tens of thousands of miles old. So we picked up two fresh quarts of Castrol Dexron VI ATF and changed out the fluid in our diff. 
One of the great things about being relatively skinny and working on a VX is that a jack is only needed for jobs that require the removal of wheels. The TOD is easy to get to, but due to its close proximity to the exhaust, it's best to work on it when the truck is still cold. It's a simple enough job: drain the old ATF out of the bottom hole (on the right), close, and fill from the top. The t-case takes just under 2 quarts. A hand pump makes the job of refilling the diff a snap.
The fluid that came out could barely be described as ATF. It was black and smelled of slightly burnt clutch. Yeah, we'll take a wild guess that this is original Isuzu ATF. After finishing this job, our TOD trouble went away completely within a week. We were right again! Once the new ATF had permeated all of the working bits of the transfer case, the clutch plates slipped along just as they are supposed to. With the fluid looking this bad, we ended up doing a second flush 1,500 miles later, just to be sure we had cleaned out all the burned up fluid and any debris it may have left behind. The TOD now works perfectly, kicking in right when we need it. It really helps pull the front of the truck into line when you roll into the throttle. If you want to see how well it really does, petition Central Region Kentucky SCCA to let our Project VehiCross onto an autocross track!
With the TOD fixed, we moved onto the axles. We noticed some drivetrain noise a month after we bought the VX. Once again, we suspected old fluid. Once again, we were not disappointed. The oil that came out of the diffs had severely broken down and was now black sludge. Honestly, we wondered if someone had accidentally filled our diff with old sewage instead of oil. We did the change in the middle of winter and the oil came out as runny as the ATF in the transfer case. This oil was doing nothing to lubricate our diff and axle bearings anymore. Good riddance!
We replaced the destroyed diff oil with Lucas Heavy Duty Gear Oil. We chose Lucas for two reasons: the first is because Lucas oil is compatible with limited slip differentials. Since the VX is equipped with a clutch type LSD from the factory, this was important to keep the diff happy. Second, Lucas diff oil is not a full synthetic. While a full synthetic would probably last longer and allow our diff to run cooler (which will be important when we begin to tow), full synthetics can sometimes damage factory seals and gaskets, causing leaks. Knowing the VX is saddled with quite a few design flaws (hey, what can you say about a car company that was owned by GM and forced to partner with Lotus?), we thought it best to skip the synthetic fluids and avoid a potential leak. The last thing we wanted was to have to rebuild either axle! The front takes 1.5 quarts of 80W-90 and the rear uses 2.5 quarts of 90W-140. How that turned into a fiasco is well documented. However, the effort was worth it. Not only did we come up with a unique Wrench Tip, but we also solved the drivetrain noise.
One thing to note in the VX (and I assume the Trooper as well) is that on the front diff, the oil drain plug is also one of the carrier mount bolts. Remove the lower passenger bolt and the oil will drain out. You will need a bit of silicone to reseal the threads. The rear diff is much more straight forward as it has dedicated drain and fill holes. With the VX's short overhangs, it is also much easier to work on.
On the left is the ATF from the second t-case flush. On the right, is oil from out front diff (we took this pic a month after the flush, so the dirt had mostly settled out of it and it looks a lot better than it did when we first drained it). In the middle? That's the ATF from the first t-case flush. Yikes. Dexron is supposed to be red, not brown. No wonder we were having so much trouble with the 4WD.We still need to flush the coolant and the brakes. We think some fresh Motul 4.5 brake fluid will take care of our spongy brakes once and for all. Some new coolant should help us when we are ready to start towing. We still need to take care of our worn out Nexen tires and our brake pads are getting a bit thin too. Oh hey, speaking of towing, we need to figure out a hitch and transmission cooler. But for now, we are basking in the glory of turning our unloved truck into a reliable daily driver. Now we just need to find some trails to take it on…
