ARB Air Compressor Install on Jeep CJ-7

Dec. 03, 2013 By Jim Brightly, KF7SCT
With two people and two dogs onboard, there’s not a lot of room left over in a CJ7, so not having to carry a portable air compressor makes a lot of sense. With a Chevy 350, Terraflex 4:1 low range, 4.56:1 gears, ARB lockers, and Goodyear MT/R tires with Kevlar, the 1982 CJ7 has little trouble with technical trails up to four-plus ratings.

In my opinion, a selective locker—especially in the front differential—is the best of both worlds. Whether it’s an electrically controlled locker (as is in my ’07 JK Rubicon Unlimited) or an ARB air locker (such as I have in my 1982 CJ7 hard-trail (4+) Jeep), a selective locker up front allows you to engage and disengage as you wish so that you can negotiate more easily the very tight turns on very technical trails. A selective rear locker, while not nearly so attractive, is just icing on the cake or the cherry on top of a hot fudge sundae.

I assembled all the components on the Jeep’s tailgate prior to installation.

“Why is a selective locker in the front differential better?” You might ask. Because a locker, by definition, applies equal torque to each tire, unlike an open differential, which applies torque differentially, allowing the tire on the outside of a turn to travel a longer distance than the tire on the inside of the turn. If you’ve ever taken notice of your tire tracks in snow, sand or dirt, you know what I’m talking about. And if you’ve heard a vehicle equipped with a rear locker making a tight turn on pavement, you’ll remember the “chirping” of the rear tires as the inside tire intermittently skidded slightly on the pavement to relieve the stress on the rear axles. With a front axle, when the locker attempts to apply power equally, the tires want to go straight. Even with the assist of OEM power steering, from a driver’s perspective, the steering wheel inexorably tries to spin until the front tires are parallel. If you’ve equipped your Jeep with a hydraulic ram steering assembly, you might be able to hold it in the turn, but it will still be difficult. With OEM steering, if the corner has a decreasing radius—it gets tighter the further into the curve you go—you’ll find you can’t turn the wheel. It’s as if the ignition lock was applied, or it slowly turns in the other direction. And the more power you apply, the harder it is to hold the steering wheel. That’s why auto manufacturers, even with trucks having OEM lockers, tend to offer either selective lockers or limited slip units for the front differentials.

Initially I ordered the ARB one-gallon aluminum air tank, but again the lack of room in a CJ and the fact that the Jeep has a sealed front bumper that could be used as an air tank convinced me to set it aside.

ARB now has several models of high-performance compressors, including dual-cylinder and single-cylinder designs. Although this high-output compressor comes equipped with a manifold (for use with air lockers only), I opted for a separate manifold.

A separate manifold allows me to use the system for air tools, filling tires, as well as operating the air lockers.

The optional air hose will reach all tire positions, even full-size pickups and duallies.

However, unlike the Rubicons’s selective lockers, ARB air lockers are available aftermarket for those older vehicles that were sold without lockers being factory (or OEM—or original equipment from the manufacturer) equipment. When my Seven originally rolled off the dealership’s floor more than 30 years ago, the best its owner could hope for were 4.10:1 gear ratios and limited slip traction aids (called Trac-Loc). (An old trail saying indicates that the “only thing a limited slip differential limits is the amount of traction.”) My CJ7 did not even have a Trac-Loc.

This is the 20-year-old ARB compressor. I found out after its removal that it still operates; a couple of other electrical problems caused the ARB system to quit working.

But as I said, I’ve had ARB lockers in my ’82 Seven for more than 20 years without a major problem. The only problem I’ve had with the ARB units was a cracked copper tube shortly after the initial installation (I had the 4.56:1 gears installed at the same time as the ARBs—replaced 3.73:1 gears, as I recall). Of course, even though ARB may not recommend it, I never engage one of my ARBs while the Jeep is moving, and I avoid disengaging them while moving. As far as I know, ARB has no official opinion on this subject, but I prefer playing it safe by stopping first before flipping the ARB switch. For more information on my Seven’s differentials, check out this story.

As much as I love my ARBs and 4.56:1 gears—and I do!—with this upgrade, I didn’t touch the differentials and/or lockers at all. My entire attention was devoted to the “upper” portion of the ARB system. Recently, I became aware of ARB was offering compressors with high performance figures than my 20-year-old ARB compressor possessed. At about the same time, my compressor quit working. This prompted me to begin thinking about an upgrade. A combination of work, vacation plans, and having the 2007 JK Rubicon Unlimited at my disposal caused me to forget about the CJ’s non-working compressor until I began this install.

My 1982 CJ7 is an old, hard-working Jeep, and it has collected a lot of miscellaneous extraneous wiring over its lifetime. The inner fender well is prepared to accept the new compressor. I removed the old compressor and the Jeep’s horn, and moved the electric fans’ adjustable thermostat to clear some space.

All I was concerned with when starting this upgrade was improving the CJ’s capability of having onboard air for the tires and trail tools. I wasn’t concerned with the differential side of things. If you have a vehicle equipped with ARB lockers, and the system is getting a bit long in the tooth, you might want to consider this upgrade yourself. And then you can leave the portable air compressor at home. Or if you don’t have ARB lockers, you could still add this system to your rig and be able to air-up at your convenience, or use air tools on the trail, or include this system with ARB lockers rather than just a bare-bones compressor to engage the lockers.

Although the new compressor comes equipped with a new backing plate, bolts, washers, and Nylok nuts, I used some of the older hardware and saved the newer pieces.

For more information on ARB air lockers, air compressors, dealer locations, etc. see:

After mounting the new compressor in the same holes as the older one, I rotated the compressor’s barrel to more easily fit in its location.

I then mounted the external manifold close enough to be connected to the air compressor with the included stainless-steel braided air hose.

A solenoid valve must be mounted for each differential. The solenoids are manufactured from anodized billet aluminum and sealed against moisture and dust to IP54 standards, ARB’s heavy-duty solenoid controls the air locker’s actuation.

Both solenoids are mounted on the manifold and are awaiting the actuating valve to be placed on the long tubes.

Another view shows the air fitting on the manifold that will be connected with the front bumper’s fitting with a heavy-duty air hose.

In order to have easier access to the solenoid valves, I rotated the manifold in its mounting bracket to aim both solenoid tubes upward. This shows one valve in place—for the front differential—with the rear differential’s tube and solenoid ready for its valve.

This is the included pressure switch. It monitors the ARB system for sufficient pressure to operate the lockers. If the psi falls below its minimum, it turns on the compressor automatically and builds up the pressure again to its upper maximum.

All components and plumbing in place. The air lockers are working and the air pressure is being maintained.

I mentioned earlier that the system quit working. I discovered there were two problems in the existing ARB’s electrical system: i.e., a blown inline fuse and an unplugged coupler. If any of you have ever encountered two separate problems in one electrical circuit, you know how frustrating that can be. After tracing down the bad fuse, I discovered that a severe bump had caused this coupler to become unplugged. It is now secured with a tie-wrap.

With the sealed front bumper having approximately the same volume as the one-gallon tank, I drilled and tapped the bumper so it can be used as the reservoir.

A double fitting provides a glad hand for a quick coupler and also supplies the air to the bumper.

Testing out the system by filling the spare tire. Everything works well. Newsletter
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