ARB Nomenclature

The following exploded diagram and parts list are taken directly from the ARB installation manual and will help you to understand the rest of the article.

How the ARB Works

To understand how the ARB air locker operates, refer to this modified version of the exploded diagram and read the description that follows.

The air flow is represented by the red arrows.

When the locker is locked - air pressure is supplied through the seal housing tube to the seal housing (#14). It exits the port in the seal housing but is prevented from escaping by the two seal housing O-rings (#15), located between the seal housing and the seal housing running surface of the carrier. As such, the air pressurizes the cavity between the O-rings, the seal housing, and the seal housing running surface. There is a port in the seal housing running surface that directs the air into the differential where it pushes on the clutch gear (#4) that slides on the coarse splined part of the carrier (blue arrow). The clutch gear compresses the return springs (#5), and engages the coarse external splines of the splined side gear (#18). The external splines of the side gear cannot be seen ion this picture, but the engagement action is illustrated by the yellow arrows. With the clutch gear simultaneously engaging the side gear (#18) and the carrier (blue arrow), the ARB is now completely, positively locked and will act as a spool.

When the locker in unlocked - pressure is exhausted through the seal housing and seal housing tube to the atmosphere. The return springs then push on the clutch gear sliding it back against the inside of the carrier (blue arrow), disengaging the splined side gear, and allowing the differential to differentiate again. The ARB will now act as an open differential.

Installation

Step 1 - Tear Down

Assembling the ARB and Ring Gear

Note: It is at this stage that I must take one of the very few exceptions I have to the ARB instructions (as I said - they are excellent overall). However, the ARB instruction sheet includes this step:

"Apply a thin film of high pressure grease to the ring gear shoulder of the Air Locker to prevent seizing."

I fundamentally disagree with this step. First - the ring gear and air locker will spend their life running in an oil bath - it is very unlikely that seizing due to corrosion will ever happen. In fact, I have never seen a ring gear seized to its carrier. Some are very tight, it's true, but that's a good thing - a very good thing.

More importantly though - you actually want a very high friction interface between the ring gear and the locker - you want the ring gear bolts to clamp the ring gear to the flange on the locker - thereby achieving friction between the two - and thereby keeping the ring gear attached to the locker, without having to rely solely on the ring gear bolts loaded in shear. I believe coating either side of this mating interface with grease - or anything else - would be highly counter-productive. Keep the surfaces clean and dry.

Drilling and Tapping the Axle Housing for the Air Line

Installing ARB Into Housing

Setting Backlash and Carrier Preload

1. Remove the adjusting nut locks, washers, and bolts and set them aside.
2. Loosen the carrier bearing cap bolts until they are just snug.
3. If backlash is more than .012", loosen right-side adjusting nut one slot and tighten the left-side adjusting nut one slot.
4. If backlash is less than .003", loosen left-side adjusting nut one slot and tighten the right-side adjusting nut one slot.
5. Re-install adjusting nut locks and re-torque bearing cap bolts.
6. Re-check backlash with the dial indicator as above.

Once backlash has been set, remove the left-side bearing cap bolts, apply thread-locking compound to the threads, re-install the bolts and tighten to 135 ft/lbs.

Checking the Contact Pattern

At this stage, if all has gone well, and if you haven't changed the gears or replaced the pinion bearings, you shouldn't have to re-adjust the pinion depth. However, I recommend always checking the gear contact pattern just to be sure.

Routing the Copper Seal Housing Tube

Finishing the Air Line Connection

ARB FAQ

I wanted to add this extra section at the end of this article to address some of the misinformation regarding the ARB that I found floating around out there. Please note that these opinions and "answers' are mine alone and are not necessarily endorsed by ARB. Having said that - I am deeply grateful to Tim "The Tech Man" Lund of ARB USA for his patience answering my many questions during the research for this article.

What are the advantages to a selectable locker?

• - Driving on the street - being able to unlock the diff and run open will improve handling, reduce drivetrain shock and wear, and reduce noise and tire wear.
• Wet/icy conditions - with a selectable locker, having an open diff capability can help to keep one tire planted and prevent the rear end from fishtailing on wet or icy ground - especially side hills. Often a spool or automatic locker will cause both tires to spin and directional control to be reduced as the rig fishtails around.
• Winter driving - in winter conditions of snow and ice, a selectable locker left unlocked allows for much more predictable and safer handling. The sudden locking of an automatic locker, especially, in the front, can have quite undesirable results on a winter road.
• More fun on easier trails - by the time you've built a kick-ass rig with dual lockers you can sometimes find yourself with a lack of challenging spots to wheel. With a selectable locker you can leave the diffs unlocked and have more fun on the easier trails with family and friends.
• Cutting brakes - with a selectable locker you can get better performance from your cutting brakes for superior turning without undue stress on the drivetrain.
• Locked is locked - most advantages to a selectable locker revolve around being able to unlock the diff. However, one other advantage is that, once locked, it will never accidentally unlock on you, the way an automatic locker can.

There are many more, I'm sure, but they all boil down to ultimate flexibility. With a selectable locker you have the choice of when it is locked or unlocked.

Is an ARB any less reliable than other lockers?

No, not if it installed and maintained properly. Sure, there are more parts and installation is trickier - but this true of many other components you'd never consider inferior because of their complexity. EFI is more complex, has more parts, and is more difficult to install than a carb - but no one in their right mind would choose a carb over EFI because there are more parts in an EFI system. A coil-over 4-link suspension is more complex than leaf springs - but for extreme use, it's clearly the better choice. Heck - there are more parts and greater complexity in a car than a horse-drawn buggy - but you don't see people running the Rubicon on wagon wheels!

But what about those who claim they prefer a simple automatic locker?

Well, there is always a tendency for folks to defend whatever system they choose to run - it's normal and it's natural. But let me ask you this: how many folks running automatic lockers have also run an ARB? Better yet - how many folks have run automatic lockers, upgraded to an ARB selectable, and then decided to switch back because they liked the auto locker so much more? Not very many!

Isn't the supplied blue plastic air line a weak link?

Yes, and it's supposed to be. It is what is known as an "engineered weak link." Yes it is weak and easy to break, because it is supposed to be. This is so that, if you snag an air line, it'll break and can easily be repaired in the field with a splice or a new ferrule in a couple of minutes. However, if you run stronger air lines (like stainless steel or hydraulic hose) and you snag a line, the line may not break. Instead you end up pulling the fittings out of the axle or the compressor. This is much more difficult to fix.

Having said that - proper routing of the air-line is critical and will go a long way to ensuring failure-free operation. Make sure you route it well, tie it down every 12" or less, and keep it away from heat, vibration, sharp edges, and the like. No two installations will be exactly the same - but common sense and a good plan will help. Routing it along-side flexible brake hoses is one good option. In terrain where there is a lot of brush, bushes, logs and other debris, abrasion damage to the line can be minimized by protecting it with a sleeve of vacuum hose or wiring loom - without loosing the desired weak-link feature.

How can I patch a hole in my air line?

Quite easily. The best way is to replace any damaged section with a new piece of line and some splice fittings. ARB supplies metric push-lock fittings for this purpose. In my experience, you can also splice a line with standard 3/16" compression fittings - the type that use a threaded body. a ferrule, and a compression nut. Since the ARB line is 5mm, which is slightly larger than 3/16", you may have to lightly sand the end of the air line with a piece of emery cloth or sand paper, to get the 3/16" ferrule to fit on - but once assembled it works quite well. Often, several varieties of air-line fittings can be found at heavy-duty truck parts suppliers or other outlets that cater to vehicles that use air brakes.

In a pinch, successful field repairs of the air line have been accomplished using epoxy, steel putty, JB weld, vinyl tube and super glue, and even the ubiquitous duct tape!

Where can I get replacement parts for my ARB?

Parts and accessories are available direct from ARB or from any one of a large international network of retailers. ARB can be reached at (425) 264-1391

Will I / Why do I get gear oil coming up the air lines?

You should not have gear oil being forced up the air supply line. If you do have this condition - it is an indication that there is some sort of problem. A properly installed and functioning ARB will run at any angle and not cause gear-oil to come up the air line. The most common causes of this problem are:

- A blocked differential breather valve/line is allowing high temperatures to generate sufficient pressure inside the diff to force gear oil past the seals and up the air line.
- Warn, damaged, or improperly installed (twisted) O-rings in the seal housing are allowing gear oil up the air line when the air locker is unlocked and pressure is vented to the atmosphere.

The easiest way to determine which problem is affecting you is to disengage the locker and drive normally for a week without using the locker. If you still get gear oil out the air line - a lack of sufficient axle housing venting is the likely cause. If you don't have any signs of oil after the week, engage and disengage the locker several times. If oil is now present, it indicates that the oil is travelling up the line when the locker is depressurized - meaning the seal housing O-rings are the likely culprit.

What are the most important things to watch out for when installing an ARB?

Care and cleanliness are obvious - as is reading the directions thoroughly first. In addition, special care should be taken to:

• Thoroughly clean the seal housing before installing the O-rings. Sometimes excess packing grease can be present that can interfere with proper installation and operation.
• Generously lubricate the seal housing, O-rings, and seal housing running surface before installing the seal housing.
• Make sure the seal housing O-rings are not nicked, cut, twisted, deformed, or otherwise damages before and during installation.
• Set and maintain sufficient carrier bearing preload to prevent damage to the seal housing.
• Not over tighten any axle housing fittings.
• Keep any and all debris, dirt, or foreign objects out of all fittings, air lines, and the locker itself.
• Set up the gears properly and accurately after installing the ARB.
• Carefully route the air-line away from heat, vibration, and sharp edges - tying it down securely every 12' or less.
• Supply the ARB with clean, dry air between 85 and 105 psi.
• Keep the gear oil clean while the locker is in service to minimize the chance of debris damaging the seal housing O-rings.

How many models require drilling of the bearing cap during installation?

Few models require drilling of the bearing cap for the seal housing tube anymore. The Dana 60 is probably the only common model still requiring this step.

What sizes are the O-rings used in the ARBs?

They are all standard, common sizes - nothing custom.

In order to order an O-ring you need to know two things - the size and the material.

O-rings come in a variety of different materials, depending on their use. The two most common are Nitrile (Buna-N) and Viton. The following table illustrates some different O-ring materials and their properties. Note that in the "Material" column, where it says, for example "Standard: 70 Durometer Black" this indicates the standard hardness of the material (durometer is a reading of hardness - you may see it quoted by racers when referring to how hard or soft a tire's rubber compound is) and the standard colour of the O-ring

To make things easier when specifying an O-ring, there are two common international O-ring standards that can be used.

The first is the AS568A standard. It consists of a "dash number" that allows both the ID and the CS to be called out by a single number. For example, an O-ring that is "dash 151" has an ID of 3" and a cross section of 3/32". The AS568A dash number doesn't tell us anything about the material though - so if we order by AS568A dash number, we still have to specify the material - for example: "I'm looking for a dash one fifty four in Nitrile".

The other standard is the British Standard (BS). This is the most convenient standard, as any O-ring's BS number identifies not only the precise size but also the material. It does so by using a prefix equal to the AS568A dash number, coupled with a letter and two numbers that identify the material and the durometer (hardness) of the material. N denotes "Nitrile" and V denotes "Viton". For example, an O-ring that is BS 151N70 is an O-ring that has a 3" ID, a 3/32" cross section, and is made of Nitrile durometer 70.

You can find the size of the O-rings required for your ARB from the following table. To use the table, you must know the ARB part number for your particular locker. If you don't know it, you can find it by looking in the North American ARB Application Catalogue or the International ARB Application Catalogue or by examining the ARB application lists that follows the O-ring table.

ARB O-ring Table

ARB Applications - International

ARB Applications - North America

Why all the metric air line and fittings?

Quite simply because ARB is an Australian-based global company. Most of the planet uses metric - Australia, Great Britain, Europe, Japan, Canada, South Africa, South America, etc. Some countries, like Canada, have both standard and metric fittings readily available. It seems that only in the USA are metric line and fittings hard to come by - although with increased globalization even this becomes less true as time passes - for example, there's not a car manufactured in the US today that doesn't use at least some metric fasteners. All this is, of course, not terribly helpful if you happen to live in a region where metric parts are hard to come by. If this is the case, you have several options: 1) Use the ARB supplied parts and source metric replacements directly from ARB or one of their distributors 2) Use the ARB supplied parts and the closest fitting standard parts if you need replacements - such as using 3/16" compression fittings with the 5mm air line or 3) Convert your system to standard (SAE & NPT) sized components (see below)

What are the threads on the axle housing bulkhead fitting centre compression nut?

3/8"-24 UNF

What are the threads in the ARB solenoid? Can I use a 1/8 NPT fitting?

1/8" BSPT (British Standard Pipe Tapered)

BSP stands for British Standard Pipe, of which there are two types: parallel and tapered. BSPT is British Standard Pipe Tapered and BSPP is British Standard Pipe Parallel. Obviously one has parallel threads and the other, tapered threads.

BSP threads are common in gas and pneumatics (indeed, you may see BSP threads referred to as "Gas" or "G", as in "that fitting is 1/8-G")

BSPT threads are very similar to, but not exactly the same as NPT threads, as the following diagrams and charts illustrate:

You can also see from the charts that 1/8 BSPT is 28 Thread Per Inch (TPI) while 1/8" NPT is 27 TPI. Many people have reported success screwing a 1/8" NPT male fitting into a 1/8" BSPT and achieving a leak free connection by using a lot of Teflon tape, plumbers dope, or thread locking compound.

The better way to do it is to use a BSPT to NPT conversion fitting. These are available from good hydraulic or pneumatics suppliers. They are also available from auto parts suppliers often sold as gauge conversion fittings as many Japanese and European car engines will have 1/8" BSPT port for gauge sending units while many popular North American gauges have NPT sending units.

What are the threads on...

Can I convert my ARB to use SAE line and fittings instead of metric?

Yes you can, and quite easily.

The only metric parts of the system are the air line itself (5mm), and the ferrule and tube support at the bulkhead fitting (both sized for the 5mm air line). Everything else is standard size threads, except the ARB solenoids and the solenoid-air line fittings. The Solenoids have a female 1/8" BSPT thread, and the solenoid-air line fittings are male 1/8" BSPT one side and 5mm push-lock on the other side.

If you are using the ARB supplied solenoids to activate your air locker(s), and desire an NPT system from end to end, you will need to convert your air line at the solenoid end, as well as at the axle housing bulkhead fitting end. If you are using some other air supply system, you simply need to run whatever size SAE air line you choose (e.g. 3/16" or 1/4") to the axle and convert only the axle housing bulkhead fitting end.

Let's assume you want to run 1/4" air line and are using the ARB solenoids:

At the solenoid use a conversion fitting to go from 1/8" BSPT to 1/8" NPT, then a 1/8" NPT to 1/4" compression fitting, insert your 1/4" air line in the compression fitting, and run the air line to the axle, and terminate the air line with another 1/4" air line - 1/4" NPT compression fitting. You will then have to either find a fitting to convert the 1/4" NPT to the 3/8"-24 of the centre compression fitting, or you can silver-solder or braise a 1/4" NPT fitting onto either the centre compression fitting or the bulkhead fitting itself.

Of course, with the right conversion fittings and/or silver-soldering fittings to the ARB bulkhead fitting almost any combination is possible -for example you could convert to using all -AN fittings and air line if you so desired.

Will breaking an axle shaft damage my ARB?

It is possible, though much less likely than with automatic style lockers. Normally, when an axle shaft breaks with an ARB locker, if the locker is damaged, often just one of the end caps gets hogged out, which requires a relatively inexpensive repair (compared to replacing the entire locker).

Is it true that ARB made some recent design changes to the internal seals to improve performance and reliability?

Yes. The biggest change in recent times was to the internal seal. It has been changed from a O-ring or cup seal to a Bonded Piston Seal which is basically a rubber coated steel washer. The result is better cold weather performance and better sealing against excessive housing pressure.

The other reason for a decline in the number of reports of air sealing issues is attributable to much improved installation procedures, installation instructions, and installer training.

Can I use my ARB with an alternate air supply or only with an ARB compressor?

You can use any supply of inert gas (air, CO2, or Nitrogen) that supplies clean, dry gas between 85 and 105 psi. People have successfully used CO2 "Power" tanks, on-board air compressors, and even small CO2 cartridges, such as those used with paint-ball equipment. Be advised that the ARB installation manual clearly states: "ARB cannot warrant your air locker(s) against damage caused as a result of using an alternate air supply. If you have any doubts as to the suitability of your air system to use in an air locker system, consult your ARB distributor.: Note that this DOES NOT say your ARB warranty is void if you use an alternate air source - just that if you damage your locker by using this alternate source the warranty won't cover it.

Why does the factory ARB air supply installation include so much wiring?

I believe the intent of the ARB supplied wiring and switches is to allow for a clean installation in a "factory like" vehicle. The system was designed so that the switches would easily integrate with a factory dash - complete with backlit switches etc. For those of us with rugged, dedicated trail buggies that have few comforts or amenities to begin with one can always forego some or all of the factory wiring and switches in favour of a "full pneumatic" system.

How do I plumb my ARB for "full pneumatic" operation?

See ARB Install Part 2 - Supplying Air to the ARB

Why hasn't ARB ever offered a factory "all pneumatic" installation kit?

Good question!

What pressure do I need to supply to operate my ARB?

Clean, dry air regulated to a minimum of 85psi and a maximum of 105 psi

Will regulating the pressure to less than this make the seals/O-rings last longer?

No, this is an urban legend. ARB air lockers are factory tested to well beyond the recommended operating pressure. You will not cause premature wear of component failure by supplying the air pressure as required by the ARB manual.

Using the ARB wiring harness, why does my front locker only operate AFTER my rear is already engaged?

It's a built in "safety system". If both switches were armed independently, it is conceivable that you could inadvertently engage the front locker while driving down the highway - resulting in a pretty serious loss of control and the impending doom that follows. Presumably they believe that if you inadvertently engage the rear locker, potential loss of control is less (though I'd have to argue with this. Having driven automatic lockers on the highway in snow and ice I can tell you that any sudden locker activation can be pretty scary at the least). The theory is that if you have to engage the rear locker before the first there is less chance of inadvertently engaging the front. How effective this system is in the real world I cannot say. In a dedicated hard-core trail rig it has its limitations though. Imagine what a pain it would be if your rear air line is broken or the rear axle is broken or any other of a myriad of reasons why you might want to engage the front locker and not the rear (cutting brakes, for example).

Can I bypass this system?

Yes - although you do so completely at your own risk and against the recommendation of ARB.

The most common method is as follows: Unplug the yellow wire going into the centre terminal of switch #2. Run a tee from the red wire feeding into the centre terminal of switch #1 into the centre terminal of switch #2. Now when you engage the compressor switch you arm both switch #1 and switch #2.

Alternatively, you can:

Tee two wires into the red/yellow wire feeding power into the centre terminal of the compressor switch. Unplug the yellow wire from the centre terminal of switch #2. Unplug the red wire from the centre terminal of switch #1. Plug the two new wires, one each into the centre terminals of switch #1 and switch #2. Now, when you turn on your ignition all three switches run independently. This can be useful if you run a lot of water and mud as you can engage your lockers, shut off your compressor, and then charge through that deep mud hole without worrying about your compressor turning on under water.

Conclusion

If you've read this far there's very little I can add at this point that isn't already apparent. The new 14-Bolt ARB, part # RD114, delivers ARB quality, legendary ARB customer service, and great performance. The pictures speak for themselves - if you have any doubt as to the quality of this unit - go back to the first series of pictures, enlarge them to full size, and examine them yourself. I can add that, once in your hands, the physical size and weight of the RD114 is even more impressive than the pictures. To complete the package, the ARB packaging, and especially the instructions, are quite simply the best of any product I have ever reviewed. The design of the ARB is unique and keeps all the working parts protected inside the diff cover. This design also means that the ARB is probably the most challenging and tricky locker there is to install. You have to be especially careful about installing the seal housing & O-rings, drilling and tapping the axle housing, installing the carrier bearings, handling the locker without damaging the copper seal housing tube, and running the plastic air line. However, with this article and ARB's excellent instructions, any competent wrench should have no difficulty.

Immediately after installing the ARB, I took my rig on a 5-day, 1400km round-trip, wheeling adventure to the famous Paragon Adventure Park in Hazelton, PA. There I took on the toughest "red" trails I could find in the park, and while my rig suffered some severe carnage, including destroying the rear suspension, I never had a lick of trouble from my new ARB. It was reliable and trouble free the entire time, never failing to engage or disengage on my command. Not only that, but even in my dedicated, trail-only, rock-buggy it was a real treat to be able to lock or unlock the rear diff at will. Having lived with a spool for several years I found myself suddenly spoiled with the ability to make tighter turns, optimize my cutting brake performance, and even enjoy wheeling some of the easier trails with open diffs again.

Best of all - ARB have all but eliminated any argument challenging the superiority of the mighty 14-Bolt.

Go to >>> ARB Install Part 2 - Supplying Air to the ARB

References:

• ARB Air Locker Installation Guide. 2004, (ARB Corporation Limited)
• Chevrolet Motor Division 1981 Unit Repair (Overhaul) Manual . 1980, (General Motors Corporation)
• US Military Intermediate Direct Support/General Support Maintenance manual TM 9-2320-289-34. 1992, (Department of the Army, The Air Force, and Headquarters, Marine Corps.)
• Yukon Gear and Axle Installation Kit Instructions