When we put an air locker in the rear of our Project Hatari! CJ-6, we decided to install a dedicated onboard air system not only to run the locker but to better complement this vehicle's alter ego as a do-all recovery vehicle. We already had the capability of running power tools and welding thanks to the Premier Power Welder. Then we figured with a 100-percent duty cycle compressor and three-gallon air tank, we'd have the capability of running air tools, inflating hundreds of tires, or keeping one of those dancing car lot gorillas gyrating at camp.
Since we already had an old three-gallon air tank on the shelf, we only needed a heavy-duty compressor. We wanted something with a 100-percent duty cycle that wouldn't fry during heavy, extended use. For protection from the elements and thieves we'd need to mount it under the dash on the firewall, so we needed a unit that could also run in any position. Finally, we needed something that could fill our tank quickly because we're impatient buggers.
The MaxAir 4.0 compressor from 4WD Products fit the bill. The compressor can be run upside-down and sideways if needed. The compressor head can be rotated for clearance (our application didn't need it) and the air filter can be installed either on the unit or remotely. Here's the system we put together. We're now a rolling repair shop in the back country looking for broken damsels in distress.
We mounted our compressor straight to the firewall with some poly shock bushings. We were nervous about vibration, but the MaxAir 4.0 has proven to be a smooth operator and doesn't shake the dash apart when powered up. | 
Here's 4WD Product's suggested plumbing diagram. We followed the company's wiring schematic. The compressor is capable of 150psi max pressure and its 34-horsepower motor draws 40 amps at 150psi and 30 amps at 35psi. It can deliver a continuous 4.0 cfm, yet it only weighs 17 pounds. If fills the three-gallon tank, runs very quietly, and is mounted completely out of sight. | 
Our tank has several fittings. We used an in-line check valve between the compressor and tank so the pressure wouldn't bleed down. The trick big-rig type plastic pressure hose and fittings our Teraflex T-Locker uses are in the foreground. More on that in a later issue. Behind it is our pressure switch that engages the compressor when pressure drops below 90psi and shuts it off when pressure reaches 120psi. |
You must run the supplied stainless leader hose because of the heat generated by the compressed air as it leaves the piston. We mounted an air chuck to the leader and secured it to the firewall just in case we ever wanted to bypass the tank and hook our air line straight to the compressor. We used a standard 3/8-inch pneumatic hose to plumb back to the tank. | 
The tank mounts in the CJ-6 under the floor beneath the rear seat. An air chuck is mounted within easy reach on the side for filling tires and running air tools. We used a 130psi blowoff valve on another tank fitting to ensure the pressure never rises to dangerous levels. | |