2001 Nissan Xterra - Differential Buildup

We need lockers and gears, and we not only need them, but we also expect them in any decently built four-wheeler. Certainly our Project Xterra, fit with extra horsepower and appropriate wheels and tires, was turning into a reliable, quality trail rig, but as we slipped over rocks and struggled up gnarly inclines, what we intrinsically knew became blindingly clear: It needed lockers and crawler gears.

Also, while we were whipping lockers into the differentials, this would be the perfect opportunity to swap out the X's stock 4.36 gears for a set of 4.88 gears from Nissan Motorsports. The ratio is a bit low, really, for our 31-inch Baja Claws, and makes the Xterra a bit buzzy on the highway. But it improved the X's crawl ratio to 35.3 from the stock 31.5. Add to that a significant reduction to the Xterra's low-range ratio and what we now have is a crawl ratio of 68.5:1.

To enhance the X's streetability, the lockers had to be selectable. We called ARB, knowing the company made a rear locker for the Nissan. Serendipitously, it turned out the company was developing a front locker for the Xterra. We got our hands on a prototype and headed over to the pros at Tri-County Gear, in nearby Pomona, California, to install the new lockers and gears.

Setting up new gears is truly a science in and of itself, requiring special tools and plenty of know-how. Unless you're schooled in the task, don't try setting up a diff on your own. As one of the Tri-County pros told us, "Proper setup can make the difference between your differentials lasting 3,000 miles or 100,000 miles."

Once we got the gears and lockers set up, we turned our attention to the Xterra's transfer case. Nissan specialist CalMini recently introduced a 3.92:1 low-range gear reduction for Nissan transfer cases.

We got a set, had the techs at Four X Doctor drop them in and hit the rocks. Here's a chronicle of our time at the shops. Special thanks to everyone at Tri-County Gear in Pomona, Off Road Unlimited in Burbank (ARB air compressor) and the Four X Doctor, also in Burbank (T-case gears).

Front Diff

The IFS of the Xterra features two halfshafts, making diff removal easier than you might expect. Drain the pumpkin, remove the front wheels and unbolt and remove the skidplate. Remove the front crossmember. To access the differential mounting bracket, we had to pull our steering stabilizer. Unbolt the differential from the bracket and disconnect the halfshafts. Don't forget to unplug the vent hose, a commonly overlooked step. Finally, unbolt the driveshaft and pull the differential.
Front Diff The IFS of the Xterra features two halfshafts, making diff removal easier tha
Pull the axleshaft and pry out the carrier and ring-and-pinion. We retained our carrier's bearings, since our Xterra had just 15,000 miles on it. The lip of the diff housing where the pinion seal fits must line up exactly when you're done. Here, our mechanic measures the preload on the gears at 5 in-lb. Since we're keeping our original bearings, this was the rating we'd work toward with the new ring-and-pinion. With new bearings, we'd set preload somewhat higher, probably at about 10 in-lb.
Pull the axleshaft and pry out the carrier and ring-and-pinion. We retained our carrier's
Remove the pinion yoke with a 1 1/16-inch socket. Save the shims on the pinion. These help set the preload rating. When installing the locker we used the OE bearings. If you use the same gears, make sure the height where the new ring gears sit matches the old carrier height. Since we were unable to pull the pinion race (a sleeve that fits between the pinion and the housing), the guys at Tri-County used a bearing spreader.
Remove the pinion yoke with a 1 1/16-inch socket. Save the shims on the pinion. These help

Our mechanic press-fit the bearing onto the pinion. After lubing the race inside the carrier, he gently taps on the pinion, being careful not to damage the pinion seal. Once in, tighten the pinion yoke so that the pinion does not "walk." You may tap it with a rubber mallet to get it seated properly.
Our mechanic press-fit the bearing onto the pinion. After lubing the race inside the carri
Take the ring off the factory carrier. Using the OE bolts, bolt the new ring to the ARB carrier and bearings. Then, press the bearing onto the carrier housing. Grease the ring gear and position it in the carrier. Spin it a few times by turning the pinion yoke. The grease should spread evenly on the teeth of the ring gear. The backlash, or amount of play on the housing, should measure 0.008 inch. This is achieved through trial and error-a trying process that illustrates exactly why such installs should be left to the pros.
Take the ring off the factory carrier. Using the OE bolts, bolt the new ring to the ARB ca
Finally, install the air line, making sure it doesn't touch any parts, especially the ring gear and the carrier. Work carefully not to crimp the line. Attach the two provided ferrules. The one with the flat end fits on the outside of the tube. Test the pressure in the line. Our prototype needed an elbow to fit outside the carrier that would connect it to the air lines, so the guys at Tri-County fabbed one up. (ARB will include all necessary parts when this locker goes into production.) Once preload and backlash are adjusted to their proper settings, return the axletube to the diff and reattach all the frontend parts.
Finally, install the air line, making sure it doesn't touch any parts, especially the ring

Rear Diff

Start by removing the wheels and disconnecting the driveshaft and brake lines. Unbolt the diff housing and pull the rear carrier. Disconnect the main pinion seal. Pull the yoke nut and separate the pinion from the housing. Then remove the OE ring gear and keep the bolts for the ARB housing.
Rear Diff Start by removing the wheels and disconnecting the driveshaft and brake lines.
Install the ARB carrier and tighten the bearing cap. Again, using trial and error, adjust the backlash of the carrier so that it can move only 0.008 inch. Install the air line and bend it to the exiting hole. Return the carrier to the housing and reinstall.
Install the ARB carrier and tighten the bearing cap. Again, using trial and error, adjust

Air Compressor

The first question in installing the ARB's air compressor is, "Where?" So we went to Off Road Unlimited in Burbank. There, we found enough room inside our ARB front bumper to mount the compressor.
Air Compressor The first question in installing the ARB's air compressor is, "Where?" So
The next question is where to install the lockers' switches. We found the perfect spot on the plastic console right behind the shifter. ORU pulled the console, measured out enough room for three switches, cut the plastic and routed the air lines. Lovely.
The next question is where to install the lockers' switches. We found the perfect spot on
Transfer Case

Because you must remove the Xterra's torsion bars to get to the T-case, first measure the ride height at both sides of the front end. The top of the fender lip is a good place from which to measure. Drain the T-case and disconnect the rear driveshaft. If the nuts are too tight, you can heat them a bit with a propane torch. (Kids, try not to set your truck on fire when you do this.) Then disconnect the T-case shifter linkage seen here. Index the torsion bars and remove them. Note: the torsion bar adjusters can be tricky to pull out. Remove the front crossmember. (If you have a manual transmission, drain the tranny too.) Finally, disconnect the electrical connections to the 'case.
Transfer Case Because you must remove the Xterra's torsion bars to get to the T-case, fi

Pull the T-case and bring it to your workbench. Remove the check balls and springs. Remove the neutral switch and the 4H/L speedo gear. Separate the rear output cover and pull the plastic oil gutter. Then remove the idler and input gears. After separating all the gears from the T-case housing, clean each component thoroughly. Once clean, remove all the factory silicone and grease the seals so that they do not get reassembled dry.
Pull the T-case and bring it to your workbench. Remove the check balls and springs. Remove
Once the 'case is clean, you'll have to make room for the larger gears inside the housing by trimming/cutting a total of about 11/48 inch off the transfer-case housing. Put the new low output gear inside the housing and mark where it makes contact with the oil gutter. Mark the depth of the cut. Then, measure and mark the gutter in the center T-case housing. Use a circular saw to grind away just enough material to make room for the gears.
Once the 'case is clean, you'll have to make room for the larger gears inside the housing
Next, grind a relief into the bump that is located in the front housing next to the large end of the countershaft gear. Again, make very sure that you don't grind off more than necessary. Then cut a small notch into the shift fork. Now that you've customized your T-case for CalMini's crawler gears, you're ready to reassemble the T-case and reinstall it. Start by pulling the bearing from the large end of the countershaft gear. Press the CalMini-supplied bearing onto the small end of the new countershaft gear. Then do the same for the large end of the new gear.
Next, grind a relief into the bump that is located in the front housing next to the large

Remove the bearing retainer clip from the old input gearshaft and separate the bearing from the input shaft using a bearing splitter. Then, pull the bearing from the OE input shaft and install it onto the new input shaft. Reinstall the retainer clip.
Remove the bearing retainer clip from the old input gearshaft and separate the bearing fro
Install the countershaft-bearing reduction collar into the centersection of the case so that it is flush with the housing. Install the needle bearing onto the mainshaft and apply some lube, then install the new low output gear on the mainshaft. Install the high and low hub on the mainshaft, then reinstall the hub retainer.
Install the countershaft-bearing reduction collar into the centersection of the case so th
After lubing the case housing and reinstalling the counter gear assembly, reinstall the input shaft at an angle and slide it into place. Apply silicone and reinstall the T-case cover. Then install the interlock plunger pin, making sure it is in the case between the holes for the shift rails. Install the high- and low-range shift rod and fork. Then install the 2WD/4WD shift rail, apply silicone to the edges of the case, and reconnect the parts.
After lubing the case housing and reinstalling the counter gear assembly, reinstall the in

Install the snap ring on the shift fork and then install the oil gutter and cover. Rebolt the rear T-case cover. Return the transfer neutral position switch, check balls, springs and plugs. After installing the speedo gear, check for unplugged holes where the check balls go. Then rotate the driveshaft output to check for binding. Reinstall the transfer case. You're done. Go rockcrawling!
Install the snap ring on the shift fork and then install the oil gutter and cover. Rebolt

SOURCES
ARB 2-06/-264-1669 www.arbusa.com	Calmini www.calmini.com
Off Road Unlimited www.offroadunlimited.com	Nissan Motorsports
Tri-County Gear 9-09/-623-3373 www.tricountygear.com