Understanding the ARB Air Locker System

The ARB Air Locker is widely regarded as one of the most reliable and effective selectable locking differentials on the market. Unlike automatic lockers that engage unpredictably, the ARB Air Locker gives you on-demand traction with a simple dash-mounted switch. When the locker is disengaged, the differential acts as an open diff, allowing normal on-road driving with tight turning radius and no tire scrub. When engaged, compressed air pushes a locking collar that positively locks the left and right axle shafts together, delivering 100% torque to both wheels. For Dana 44 axles commonly found in Jeep Wranglers, Ford Broncos, and Chevy K5 Blazers, the ARB RD124 or RD23 locker kit is a popular upgrade for serious off-roaders.

This comprehensive guide walks you through the installation process from start to finish. Whether you are an experienced gear installer or a confident DIY enthusiast, following these steps ensures that your locker functions reliably for years. For official specs and warranty details, consult the ARB Air Locker product page and your vehicle’s service manual.

Why Install an ARB Locker on a Dana 44?

The Dana 44 is a legendary axle—a strong middleweight that balances weight, strength, and aftermarket support. Adding an ARB locker transforms a capable axle into a dedicated off-road weapon. The key power gains come from the ability to lock the differential when you need maximum traction in rocks, mud, or sand, and then unlock it for daily driving. This flexibility means less wear and tear on drivetrain components, improved fuel economy on pavement, and the confidence to tackle obstacles that would leave open-diff vehicles spinning helplessly.

Beyond traction, an ARB locker allows you to run larger tires and more aggressive lines without breaking traction. You also avoid the harsh engagement of lunchbox lockers that can make tight turns dangerous on slick roads. When paired with a quality on-board air compressor, the ARB system also lets you air up tires after off-road sessions, adding even more utility to your setup.

Tools and Materials

Before you begin, gather the following tools and components. Nothing derails a project faster than a trip to the hardware store mid-installation.

  • ARB Dana 44 Air Locker kit (RD124 or RD23 – verify spline count and axle shaft compatibility)
  • Gear oil (80W-90 GL-5 for most Dana 44s, check manual)
  • Differential cover gasket or RTV sealant
  • Socket set and wrenches (metric and SAE, typically 3/8” and 1/2” drive)
  • Torque wrench (capable of readings from 20 to 150 ft-lbs)
  • Breaker bar with 1/2” drive for stubborn ring gear bolts
  • Drain pan, shop rags, safety glasses, nitrile gloves
  • Jack and jack stands (or vehicle lift)
  • Pry bar or bearing puller (if carrier bearings need removal)
  • Dial indicator with magnetic base for backlash measurement
  • Air compressor and accessory line fittings (ARB recommends a dedicated compressor or at least a 2.5-gallon tank)
  • Shop manual for your specific vehicle – gear ratio, tooth pattern, and torque specs vary by year and model

If you are reusing your existing ring and pinion, make sure they are in good condition. If you are re-gearing at the same time, install the new gear set before attacking the locker installation.

Preparation Steps

Proper preparation avoids costly mistakes:

  1. Read the entire ARB installation manual that comes with your locker. Pay attention to the thickness of the shims and the recommended torque for the ring gear bolts.
  2. Park the vehicle on a level surface and chock the wheels. Engage the parking brake.
  3. Jack up the axle and support it securely on jack stands. Never work under a vehicle supported only by a jack.
  4. Remove the wheels and tires to access the differential housing.
  5. If your axle has aftermarket axle shafts (like chromoly shafts), verify that the spline engagement depth is compatible with the ARB locker.

Step 1: Drain Fluid and Remove Differential Cover

Place a large drain pan under the differential. Remove the fill plug first (if you haven't already) to allow easier draining. Then remove the cover bolts in a criss-cross pattern. Some covers stick fast due to RTV sealant—gently tap with a rubber mallet or use a thin putty knife to break the seal. Drain all the gear oil into the pan. Inspect the old fluid for metal shavings; heavy glitter indicates gear or bearing wear that needs attention.

Once drained, clean the mating surfaces of both the cover and the housing. Remove any old gasket material or RTV. If using a new gasket, apply a thin bead of RTV to the housing side for extra leak protection. Set the cover aside.

Step 2: Remove the Carrier Assembly

You will now remove the existing carrier (also called the differential assembly). This holds the ring gear and the spider gears. Begin by removing the bearing cap bolts – mark their orientation (left and right) since they are not interchangeable. Use a punch to mark each cap and its housing location. Place the bolts in a safe tray.

Pry out the bearing caps and carefully lift the carrier from the housing. In many Dana 44 axles, the ring gear is attached to the carrier by 8–10 bolts. With the carrier out, you can unbolt the ring gear if you plan to reuse it on the ARB locker. However, if the ring and pinion are in good shape and the pinion depth is already set, you can simply transfer the ring gear to the new locker. Important: When removing ring gear bolts, use a breaker bar and work in a star pattern. The thread-locker compound makes them tight.

If you need to remove the old carrier bearings (to reuse them on the new ARB locker), use a bearing splitter and press or a puller. Alternatively, many installers prefer to install new bearings with the locker. Consult your kit instructions – ARB often includes pre-installed bearings.

Step 3: Install the Ring Gear on the ARB Locker

Clean the ring gear and the mating surface on the ARB locker. Place the ring gear onto the locker and align the bolt holes. Apply a medium-strength thread locker (Loctite 243 or equivalent) to the ring gear bolts. Torque them gradually in a star pattern to the value specified in your manual – typically 70–85 ft-lbs for 3/8” bolts and 100–115 ft-lbs for 7/16” bolts. Do not guess; use a torque wrench. This is critical because loose ring gear bolts can shear off, destroying your differential.

Step 4: Set Gear Mesh and Backlash

With the ARB locker and ring gear assembled, you need to install it into the housing and check the backlash. Apply a thin coat of gear marking compound (prussian blue or dykem) to the ring gear teeth. Install the locker with the bearing caps loosely tightened. Spin the ring gear several times in both directions, then inspect the contact pattern. The pattern should be centered on the tooth face, not too high or low.

Measure backlash using a dial indicator. Position the indicator tip against a ring gear tooth and rock the ring gear back and forth without moving the pinion. Stock Dana 44 backlash is typically 0.006”–0.010”. If backlash is out of spec, you will need to move shims from one side to the other. The ARB locker may use spacer rings or adjustable shims – follow your kit’s instructions exactly. Setting gear mesh is the most technical part of this install. If you are not comfortable doing this, have a professional gear setup shop handle the backlash and pattern verification. Proper mesh prevents gear noise and premature failure.

Step 5: Install the Air Lines and Solenoid

The ARB lockers use a 1/4” nylon air line and a small actuator port on the locker housing. Route the air line from the differential to a solenoid valve (usually mounted on a bracket near the compressor or inside the engine bay). The ARB RD124 kit includes a bulkhead fitting that passes through a hole you drill in the differential cover. Choose a location on the cover that is not in the oil sump area and that allows the line to clear the ring gear.

Drill a 5/16” hole, deburr it, and install the bulkhead fitting with the supplied O-rings. Push the air line into the actuator port on the locker until it clicks. Route the line along the axle tube, securing it with zip ties away from exhaust, moving suspension parts, and sharp edges. Use protective loom where necessary.

Connect the air line to the solenoid – typically a 12V solenoid supplied with the ARB harness. The solenoid acts as a gatekeeper: when energized, it feeds compressed air to the locker. When de-energized, it vents the locker and allows the spring in the actuator to return the lock collar to the unlocked position.

Step 6: Reassemble the Differential

Once the air line is connected and the gear mesh is set, finalize the carrier installation:

  • Torque the bearing cap bolts to spec (usually 45–65 ft-lbs for Dana 44).
  • Recheck backlash after tightening caps. If it changed, you may need to re-shim.
  • Install a new gasket or apply a bead of RTV to the housing mating surface.
  • Reinstall the differential cover, tightening the bolts in a star pattern to the specified torque (typically 15–25 ft-lbs). Do not overtighten as it can warp the cover.
  • Be careful not to pinch the air line between the cover and housing. Many kits provide a cover with a built-in port to avoid this issue.

Step 7: Fill with Gear Oil and Purge the System

Fill the differential with the recommended gear oil through the fill plug hole until oil just starts to weep from the hole. With the ARB locker, you must bleed air from the actuator cavity during the first fill. ARB provides a purge procedure: while filling, manually cycle the locker by applying and releasing 12V to the solenoid (or activate the switch) several times. This allows trapped air to escape from the locker mechanism and be replaced by oil. Failure to purge can cause the locker to not engage or disengage properly.

After filling, clean any spilled oil from the cover and check for leaks around the plug, cover, and bulkhead fitting. Start the engine and engage the air compressor. Build system pressure to at least 100 PSI.

Step 8: Test the Locker Function

With the vehicle still raised, rotate one tire by hand. You should feel the differential operating as an open diff – the opposite tire will rotate in the reverse direction. Now engage the locker (with the engine running and air pressure sufficient). You will hear a clunk as the lock collar slides into place. Rotate the tire again – both tires should now spin together in the same direction, confirming a locked differential. Disengage the locker and verify that the tires freewheel again.

Lower the vehicle to the ground, drive it slowly in a straight line, then turn sharply in a large parking lot. With the locker disengaged, you should feel no binding. Engage the locker while stationary, then drive forward a few feet – you should feel both rear wheels pulling equally. Turn the wheel slightly – the vehicle will not want to turn easily, which is normal for a locked diff. Disengage the locker and confirm that the turning radius returns to normal.

For on-road driving, always keep the locker disengaged. Never lock the differential on high-traction surfaces like dry pavement at highway speeds – it can cause driveline binding and axle shaft breakage. The ARB system is intended for low-traction off-road use.

Performance Gains and Tuning After Installation

Once the locker is installed and tested, you will immediately notice the improvement in off-road traction. But there are additional steps to maximize performance and longevity:

  • Re-torque all differential cover bolts and air line fittings after 500 miles of driving. Initial heat cycling can loosen fasteners.
  • Change the gear oil after the first 500–1000 miles to remove any break-in debris from the locker mechanism and gear mesh.
  • Consider upgrading your on-board air system to a high-output compressor like the ARB Twin Compressor. This provides faster locker engagement and air-up capability.
  • Install a dash-mounted ARB air locker switch in a clean, accessible location. Wire the solenoid through a relay and a fused circuit for reliability.
  • If you experience slow engagement or intermittent locking, check for air leaks in the line fittings and solenoid. Soapy water works well for detection.

Many users pair an ARB locker with lift kits, larger tires, and re-geared differentials. For a comprehensive overview of compatible setups, visit the Jeep community forums where thousands of Dana 44 owners share their build experiences.

Common Mistakes to Avoid

Even experienced gear installers can make errors. Here are the most frequent pitfalls:

  • Forgetting to purge air from the locker. Follow the ARB purge procedure exactly – otherwise, the locker may not fully engage or may clunk when disengaging.
  • Routing air lines near heat sources or sharp edges. A melted or cut line leaves you stuck on the trail.
  • Using the wrong gear oil. Some limited-slip additives can damage the ARB’s internal seals. Use a standard GL-5 gear oil without friction modifiers.
  • Mixing up bearing cap locations. Caps are line-bored to the housing; swapping them ruins gear mesh. Always mark them before removal.
  • Over-torquing the ring gear bolts or bearing caps. Stripped threads in the carrier or housing can be expensive to repair.
  • Skipping the gear contact pattern check. A poor pattern leads to noise, heat, and rapid gear wear. Take the time to set it right or hire a professional.

Conclusion

Installing an ARB Air Locker into your Dana 44 axle is one of the best modifications you can make for serious off-road driving. The process is demanding but achievable for a dedicated DIY mechanic with proper tools and patience. By following this expanded step-by-step guide, you ensure that every bolt is torqued correctly, every air line is secure, and the gear mesh is dialed in for silent operation and long life. The result is a vehicle that crawls over obstacles with authority and returns to daily driving without compromise.

For additional details on the Dana 44 carrier break differences and spline compatibility, refer to the Quadratec resource center and the official ARB Air Locker documentation. With proper installation, your ARB locker will provide years of reliable performance and unlock the full potential of your Dana 44 axle.