Step By Step
Even with strain reducers and internal supports on the ARB-supplied plastic air line, a cracked hose can render your ARB inoperative (ie., open-diff operation) when you might need it most. This hose cracked right at the nut going into the ARB bulkhead fitting on the diff housing. If you don’t take the time to upgrade your lines, carry extra compression fittings to reattach the hose in the field.
The first upgrade we’ll share involves using Earl’s AN line to plumb the ARB. At the diff end, the bulkhead fitting is left in the differential housing, but the inner adapter is removed along with the old plastic hose, and Earl’s adapter PN581531 is installed. The adapter is a 3/8-24 inverted flare on one end (to mate to the stock bulkhead fitting currently used by ARB), and the other end is a male -3 AN fitting which fits Earl’s -3 braided stainless line.
Earl’s Speed-Flex hose is an aircraft-spec Teflon-lined hose with a stainless steel outer braid for the ultimate in strength and durability. However, specific assembly instructions are needed to properly cut, deburr, and assemble the stainless steel ends onto the hose. We chose the stainless fittings over the lighter weight aluminum counterparts due to their increased resistance to corrosion and stress.
A variety of configurations are available from Earl’s for end fittings such as this 90-degree version. These help route the hose around tight corners without stressing or kinking the hose, while other applications would use a straight style. We used the adjustable Speed Seal ends for precise positioning of the hose after installation.
When you secure the hose to the differential, leave enough slack for full axle articulation and attach it to the framerail, with an clamp. Be sure the hose won’t kink on axle compression, and run the hose up to the compressor location, securing the hose with clamps or zip ties. The compressor solenoids have a 1/8-inch pipe thread, so Earl’s adapter PN981603 is used to convert the 1/8-inch pipe to a -3 AN hose end fitting. Check for leaks with a soapy water solution, snug up any loose ends, and you’re done.
The second plumbing option is less expensive and uses hard brake line and rubber hose, which requires a few special fittings and tools. Jim Huff of HyTech Automotive in Las Cruces, New Mexico, showed us this method. First, the ARB-supplied bulkhead fitting (which goes in the axlehousing) is designed to retain the plastic line with a compression-type fitting, but Huff retaps it to accept 1/8-inch pipe on the internal threads. This allows standard 1/8-inch pipe fittings to be used instead of a standard inverted flare.
The copper air tube from the ARB differential sealing ring (hidden inside the diff) is cut to length and double-flared with a 5/16-inch flare nut. This is then screwed into the 45-degree-inverted-flare-to-1/8-inch-pipe fitting, which is installed in the retapped bulkhead fitting. A 1/8-inch-pipe-to-1/4-inch-hose barbed fitting is then screwed into the bulkhead fitting. A length of flexible rubber hose is then run to a 1/4-inch-barbed-hose-to-5/16-inverted flare fitting, where it attaches to 3/16-inch steel brake line that runs up to another flexible hose at the compressor.
When installing the barbed fitting, make sure you keep the bulkhead fitting from turning so the brass threads don’t get stripped, and make sure you use Teflon tape or sealer to eliminate air leaks. The barbed fittings don’t need hose clamps due to their design, and you’ll have to cut the hose off to remove it. If you want to take the hose off and on, use a regular nipple and hose clamps.
Steel brake line is run along the framerail and terminates at the compressor and differential. We chose to use stainless steel line from Classic Tube, which sells it in any desired length. Classic Tube can also supply prebent lines for brakes, fuel systems, transmissions, or any other use, and the lines come with stainless steel fittings. The lines should be secured to the frame with clamps, but zip ties will work in a pinch.
Bending a length of steel line is easiest with a hand bender for the tight turns, and stainless steel requires a bit more effort than regular steel. Once the line is installed, the ends need to be flared for the fittings. Make sure you use a proper tool for double-flaring, and don’t forget to install the line nut before flaring the end. See "Brake Plumbing" in the Oct. issue for tips ’n’ tricks.
The end of the Classic Tube stainless steel brake line is screwed into another 3/16-inch-inverted-flare-to-1/4-inch-barbed-hose fitting. Because this isolates the brake line from the compressor through rubber, any movement of the compressor won’t stress the line, which is especially important if your compressor is mounted to the engine.
After removing the snap-style fitting and hose from the ARB solenoid on the compressor, install a 1/8-inch-pipe-to-1/4-inch-barbed-hose fitting to the solenoid. Make sure you use Teflon tape, and restrain the solenoid so that it doesn’t turn. Be especially careful if you have a plastic-bodied solenoid, because overtightening the fitting can crack the solenoid housing.
For easier installation, the 1/4-inch hose should be lightly lubed before you push it over the barbed fitting. Since the air pressure on an ARB compressor is only about 85 psi, the hose is more than adequate for the pressure. The brake lines and double-flared fittings are also used in hydraulic brake systems with pressures up to 1,500 psi, so air leakage is a thing of the past.
After pushing the final hose onto a barbed fitting, fire up the compressor and check for leaks with soapy water. While not as flashy as the braided stainless optional upgrade, the rubber style will function just as well. If you can’t handle the double-flaring and running steel line, you can run rubber hose from the compressor to the differential, which eliminates another cost from the project.
The ARB Air Locker revolutionized the locking differential industry by providing the capability of switching the locker on and off with air pressure. But air-pressure actuation means some sort of air transfer lines must be used to distribute the air from the compressor to the lockers, and the supplied ARB air lines are 5mm-diameter, blue plastic tubes that have been in use for years in Australia (home of ARB). The plastic line is quick and easy to install, and for 98 percent of the 'wheelers who use the ARB system, it's relatively trouble-free.
But problems can develop over time, as the plastic line can become brittle and crack, especially if exposed to sunlight. If the line is improperly routed too close to a heat source such as the exhaust manifolds, blowouts of the line can occur. Another source of contention is the bulkhead fittings that attach the hose to the differential housing and then to the Air Locker itself. These fittings have changed styles over the years but are still susceptible to leaks, usually due to improper assembly or age, and all of these leaks can leave your 4x4 with an open differential. Also, the plastic lines that extend down to the axlehousings can get ginked due to improper routing or snagging on trail obstacles.
Many different attempts have been made to eliminate these minor shortcomings, and most have worked quite well. One really slick method is to use braided stainless line and fittings to replace the plastic line, and another method is to use steel brake line, flared fittings, and rubber hose in a unique combination that virtually eliminates any source of air leakage. Certain variations of these methods might work better on your particular 4x4, but standard fittings and parts are always the best to work with because theyre easier to source when your 4x4 is broken down just east of nowhere. Follow along as we reveal some hot tips on air line adapters.
ARB Air Lockers
Earls Performance Products
Long Beach, CA 90805