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Swap Your Axle Gears in a Weekend

Posted in How To: Transmission Drivetrain on January 9, 2019
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If your rig began as a torquey, V-8–powered truck, a set of bigger tires may not have phased it. But after adding hulking 34-inch Toyo Open Country rubber to our FJ Cruiser, it was clear the factory 3.73 axle gears couldn’t cut it. The FJ was a slug, and despite fantastic ground clearance and traction, the fuel mileage was abysmal. It was clear that we needed a gear change, but with the truck’s usage as daily transportation, the job would have to be done quickly. We’re good, but we’re not set-up-two-axles-in-a-weekend good. At least not with any degree of confidence.

To make the job quick and reliable, we turned to the folks at East Coast Gear Supply. The company specializes in Toyota axles and works with quality gear and locker suppliers like Nitro Gear & Axle and ARB. Better yet, the company offers a core exchange program. We ordered a complete front 8-inch Toyota IRS clamshell stuffed with 4.88 Nitro gears and an ARB Air Locker, and a rear third member equipped with matching 4.88s and a factory Toyota electric locker. A few weeks later a disgruntled warehouse manager radioed to tell us there were two very heavy boxes waiting for us. We unpacked two ready-to-rock axle assemblies and got to work installing them in the FJ.

While regearing an axle isn’t brain surgery, one simple mistake in the setup could cost you a very expensive ring-and-pinion. And if you’re pressed for time, there’s no beating the simplicity of a core swap. Follow along as we install a set of gears, an air-locker, and a whole lot of peace of mind.

The first step of any gear swap is to drain the old fluid. Ours was in dire need of changing anyway, as evident by its lovely black hue.
Next, loosen the rear driveshaft. It is installed with factory thread locker and takes considerable force to break loose.
With the vehicle up on jackstands, remove the wheels and brake calipers. Unclip all electrical lines, such as the wheel speed sensor lines, from the hub.
Four bolts retain the axle to the housing, located just behind the brake rotor. Loosen these and pull the axle outward. It should release without too much force.
Here you can see the loosened axle as well as the four bolt holes that secure it to the housing. The axle only needs to slide out about 4 or 5 inches to allow the axle’s centersection to drop out.
Next, loosen and remove all of the nuts from the centersection. They are located all around the perimeter. You will also need to unclip the electrical harness from the factory electric locker actuator. With all nuts removes, gentle prying action will allow the center section to tip out.
Shown are the factory center and East Coast Gear Supply center. ECGS equipped the new centersection expertly set up with 4.88:1 Nitro Gears, and it is ready to drop in.
Before installing the new centersection, clean the mating face of the housing vigorously. We used a brass wire wheel and paint thinner to remove any contaminants before applying high-end gasket maker and installing the new, ECGS center.
The electric-locker actuator can be transferred from the old centersection (if originally equipped like ours was) and reinstalled on the new one. Torque the nuts evenly around the circumference until it is tight.
Reinstall both axleshafts, plug all electric connections back in, and fill the axle up with a quality nonsynthetic gear lube. ECGS recommends Lucas 85W-140, which we used. A total fill is about 3 1/2 quarts.
With the rear axle complete, we turned to the front. Since it’s an IFS, it’s more involved than the simple yet strong solid rear axle. The process begins with removing the CV axles from both sides of the truck.
Remove the front driveshaft from the IFS clamshell.
With the front CVs and driveshaft out of the way, remove all electrical connections and the front/rear mounts. The clamshell can be tilted down and out from the crossmember.
Here is the new clamshell (left) next to the old front drive assembly. The old unit needs to be partially disassembled and the carrier section and 4WD actuator installed on the new clamshell from ECGS.
When opting for a new ECGS clamshell, we chose to upgrade the carrier to an ARB air locker. Shown is the air-line routing as installed by ECGS. This will pair nicely with our factory electronic rear locker for a fully locked (on demand) setup.
The carrier section, which allows the FJ to have equal-length CVs, unbolts with inverse Torx sockets (Harbor Freight Tools sells these) and installs simply on the new ECGS clamshell.
With the carrier assembly unbolted from the old housing, place a dab of grease on the pilot end of the shaft before reinstalling it into the new clamshell.
The carrier assembly drops directly onto the new clamshell. Use silicone sealer on the mating surfaces. Next, the 4WD actuator can be installed. Make sure the fork and collar are aligned and that collar is not engaged with the carriers splined (in 2WD).
Here, the completed front drive assembly is ready to be reinstalled in the chassis. The front CVs, electrical connections, and so on were all reconnected, and the clamshell was filled with Lucas 85W-140 gear lube. After a 500-mile break-in, the oil in both axles will be changed.
To power our ARB Air Locker, we selected an ARB air compressor. ARB offers these in several sizes, but the larger, dual unit is ideal because it has the speed and volume to air up tires quickly and the cfm to power other pneumatic equipment.
The compressor mounted easily in the corner of the FJ’s engine bay. The silver reservoir is clockable to allow for maximum clearance.
Included in the ARB kit was a wiring harness with clearly labeled connectors for power, the pressure safety switch, and the locker/compressor switches.
The compressor reaches the locker via a hard nylon line. On the compressor end, the line is push-lock, but on the axle end it is installed with a compression fitting and ferrule.
We routed the nylon line along the crossmember, securing it with zip ties, and making sure to keep it isolated from heat sources such as the exhaust, catalytic converter, and transmission cooler lines.
Here is the compression fitting on the outside of the clamshell into which the nylon line installs. Make sure not to overtighten it, as that could damage the line and cause an air leak.
The left side of the dashboard in an FJ Cruiser is easily removeable. Simply grab hold of the air vent portion and yank back and up. We stenciled out the holes for the rocker switches and cut them with a razor blade.
The pinned wires for the rocker switches are intentionally left out of the ARB connector. This lets them easily pass through a firewall grommet. Their location in the connector is labeled clearly in the instruction manual.
After a weekend’s worth of work, the FJ now features Nitro 4.88 gears, onboard air, and a front locker. Mileage has recovered by about 3.5 mpg city and 4 highway, but the improvement in acceleration and highway manners is absolutely night and day. Who says a gear swap has to be hard?


Nitro Gear & Axle
Sacramento, CA
Renton, WA 98057
East Coast Gear Supply
Harbor Freight Tools

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