Sean P. Holman
Contributor
If you wheel, chances are that you know someone, probably lots of people, with ARB Air Locker-equipped rigs. The venerable Air Locker, a popular import from the land Down Under, has proven itself a robust and reliable performer from vehicles overlanding in the Outback to rigs competing in Top Truck Challenge.
For those who might not be familiar with how an Air Locker works, it is a selectable locking differential that is paired with a source of compressed air and electronic switches for activation. This differential operates as “open” until the user pushes a button to lock the differential up, ensuring both axleshafts are turning at the same speed, regardless of terrain and traction. When the switch is pushed, a solenoid on the remote-mounted ARB air compressor opens up a port sending a high-pressure stream of air to the Air Locker, causing the clutch gear to engage the side gear. The air compressor will then run for a short amount of time to replenish the small tank of compressed air.
We have been using Air Lockers for years, and had them installed on our ’07 Jeep Wrangler project. After lots of hard miles in the dirt, our rear Dana 44 locker began to clatter on engagement and would ultimately fail to lock. We put a call in to ARB’s excellent technical support department and were invited to ARB’s U.S. headquarters in Renton, Washington, to learn first-hand how to rebuild an Air Locker. Air Lockers are fully serviceable and ARB stocks all of the Air Locker’s parts for anyone looking to rebuild their own.
Upon arrival, we met with Marc Bowers, ARB’s tech supervisor. Bowers walked us through the process of rebuilding our diff, as well as sharing tips on Air Locker operation and clearing up common misconceptions that are out there about ARB’s locker. Follow along for an overview of our rebuild and to learn a little bit more about ARB’s pride and joy.
Top 3 Common Air Locker Problems
Problem: Oil misting from solenoid valves
Solution: Axle pressurization from poor housing venting can force fluid past the O-rings and out of the solenoid. If this is happening to you, clear the vent lines and make certain any one-way valves are replaced with filter assemblies or open lines that cannot stick closed. Expanding accordion-style vents can hold several psi of axle pressure in street driven vehicles, also causing oil pumping up the lines. During normal operation the O-rings in the Air Locker need lubrication. Given enough miles the oil lubricating the O-rings can work its way up the blue line and out the solenoid. Pull the blue line loose on both ends and spray brake cleaner through the line to clean it. If the oil returns quickly something else is wrong and will need to be looked into further. If not, just clean the lines every few years as part of a normal maintenance program. Lastly, the issue could be as simple as worn parts, such as O-rings or O-ring running surfaces. Rarely is this the cause, but after a very high number of miles, it is possible.
Problem: Air bleeds past the open vent on the solenoid
Solution: Most often, a leaking solenoid valve is due to debris or build-up under the piston in the valve itself. Easily disassembled and with only one moving part, the solenoids can be cleaned and reassembled in a few minutes. Most of the time this will resolve the air leak.
Problem: Broken or melted air line
Solution: Air line problems are virtually always caused by poor planning and routing of the line along the chassis. However, if a failure does occur, then fixing it is easy if you have the required spare parts on board. Specifically, carry some spare blue air line and two ARB part number 170206 connector splices with you and the repair is as simple as cutting the damaged section, installing push-in couplers on both ends, and replacing the damaged section of line. This is a very quick and simple repair that can be done in the field, if needed.
Air Locker Facts
-ARB recommends that the throttle be closed when activating an Air Locker. Not only does it save wear and tear, but also it allows you to lock in at any speed, or even while turning.
-Air Lockers feature timed-gear technology, which means that it can only lock in the strongest position. The differential is strongest in the locked position.
-Despite being “open” when unlocked, ARB advises against using a smaller spare, as it could accelerate shim wear or potentially weld the cross-shaft to the gears. When possible it is best to lock the axle or put the smaller spare on the axle with no Air Locker, if you have one.
-Air Lockers shouldn’t be activated with less than 100 psi, but are safe and durable for up to 150-psi activations.
-Air Lockers are designed to fail in the “open” position.
With the Air Locker on the bench, the countersunk setscrews were removed and the two-piece case was separated. Older ARB Air Lockers have a three-piece case design.
After the splined side gear was removed, we were able to access the return springs, clutch gear, and bonded piston seal.
Taking a closer look at our clutch gear, you can see the culprit of our engagement problems. Note the worn edges to the clutch gear teeth (arrow). When the square-cut gear’s edges wear, the clutch gear won’t mesh, causing a ratcheting noise and more wear as it attempts to engage.
Here is a new replacement clutch gear (L) and our worn gear (R). The majority of Air Locker parts are made from strong 300M-grade steel, however, ARB uses a softer 4340-grade steel for the clutch gear, as it is designed to be an easily replaced wear item that won’t cause a chain-reaction failure.
Moving to the differential case, the countersunk retaining screws and the long cross-shaft were removed.
Next, the short cross-shafts were removed. With the short cross-shafts out of the way, the pinion and side gears can be taken out.
The pinion gears ride on a self-centering thrust washer, which can be seen here.
Looking closely at the splined side gear, you can see that the shim is damaged. This is the consequence of running with a worn clutch gear and the resulting metallic particles in the oil. Fortunately our gears were fine and all we had to replace were the shims.
Here are the pinion and splined side gears together on the bench. Notice how these gears are beveled, this is done to increase strength. The side gears are rated for 300 rpm.
After the differential case was emptied and the bearing removed, it was inspected for any damage and cleaned.
To better visualize how the internals of an Air Locker interact when reassembled, we mounted all of the components back together on the flange cap, without the differential case.
The differential case went back together in the same order as it was disassembled. Because the cross-shaft retaining pins are tapered, they don’t require Locktite.
With the differential case reassembled, we moved to the flange cap and installed a new bonded piston seal. The bonded piston seal is the heart of the Air Locker, driving the clutch gear when air is applied. It is designed to be thermally stable from -20F to 250F.
Topping off the reassembly of the bonded piston seal, clutch gear, and side gears on to the flange cap are the reinstallation of the return springs.
Here the two halves are mated before installing the countersunk setscrews that will help keep the halves together.
After pressing the bearings on, the seal housing assembly was installed so that we could bench test the Air Locker, ensuring it was working correctly before reinstallation into our vehicle.
With our Air Locker rebuilt and receiving a passing grade on the bench test, it was ready for a return to action in the back of our Jeep.
During our very typical rebuild, we replaced the following parts: bonded piston seal (A), tapered roller bearings (B), clutch gear (C), pinion thrust washers (D), seal housing assembly (E), and side-gear shims (F).
