ExtremeAire OBA

My buddy Mike had been Jeepin’ for a few years and decided he needed something more substantial than his ARB compressor for airing up his tires.  He had used it for a number of years on his 33″ tires and now that he had switched to 35″ rubber, the low airflow was r-e-a-l-l-y showing its short comings.  Mike had wheeled enough with me to know the limitations of my QuickAir2, which is also a low airflow compressor but not as bad as the ARB unit.  I honestly don’t know if he had considered a CO2 system but I do know he was in no hurry to cram more stuff under his TJ’s hood (no desire to do a York OBA).  That narrowed his choices down to an electric compressor but with reasonable enough airflow to fill the 35″ tires without taking all day. 

Enter the ExtremeAire severe duty compressor from Extreme Outback Products.  In short, the ExtremeAire uses a 12 volt 3/4 horsepower fan cooled motor to provide continuous duty (100%) airflow.  With a max working pressure of 150 PSI and a 4 CFM free flow rate, the compressor does a pretty good job filling up tires at the end of the trail.  Another local Jeeper I share trails with has been using one for a couple of years now and I’ve watched it fill his 35″ tires quite effectively.  The compressor also has a washable air cleaner on it to help keep the dust where it belongs (outside of the compressor). 

Mike stopped by my house on a Saturday to kick around some ideas of where to mount the compressor and the 1 gallon air tank he won at the 4AJUMR door prize raffle.  I had some aluminum strap in the garage and after exploring a few ideas, we decided that something similar to the above mockup could be made with hand tools and bolted into the rear of the TJ.  We took some measurements and wrote down the lengths and quantity needed to make Mike’s OBA mounting rack.

Mike was off work on July 4 and after he called me about mid-morning, I headed over to his place to help with the rack construction.  While I drove across town to his place, he made a quick trip to a nearby metal store and picked up the 1.5″ wide x 3/16″ thick steel strap we would be using.  The owner was kind enough to pre-cut the pieces for Mike.  As it was, we ended up doing a little trimming on some pieces as we got into the project but better to be too long than too short.  So armed with some c-clamps, a bag of 5/16″ fasteners fresh from the ACE hardware store, and the cut metal, we started building the mounting rack.

The first step was to rough out the location and spacing for the rack.  A piece of 2×4 held up one end while we checked for proper clearance on the compressor and tank.  Although Mike is running a hard top now, he wanted to be sure he could properly fold a soft top down along the side of the rack without hitting the compressor or air tank.  This was one of those projects where you wanted to measure twice and only cut once. 

After trimming a couple of the rack pieces to the proper length, Mike fired up the old drill press and put a few holes at what we hoped would be the correct locations.  As it turned out, our measurements were right on the money and no holes had to be slotted or elongated in order for everything to bolt together.

With the requisite holes drilled in the pieces, we staged the compressor and air tank on the floor with some bolts in the holes to make sure we hadn’t missed anything.  A quick hardware count revealed we had actually gotten enough of everything needed except for one bolt.  We hadn’t counted on the extra length needed for one of them that went through some extra brackets that were used by Mike’s old tire carrier.  No problem, what we had would work for the test fit and he could pick up the rest during the next trip to the hardware store.

Here is the first test fit.  It all went just where we wanted it to go.  We drilled a half dozen holes into the fender well area to finish up the mounting points.  The last thing to do was the bracket to support the end of the rack.  You can see it attached to the bolt on the air tank.  At this time, Mike is not sure if he will need another bracket to support the rack under the compressor.  The bracket was formed by spending a few minutes with the vise and a very big hammer (yeah, not the most elegant manner but it did the trick and turned out nice).  Edit:  Since Mike had the material on hand, he bent another bracket, similar to the first one, and located it under the compressor.

Mike didn’t need help with the disassembly and painting.  He will do that during the evenings when he gets a bit of spare time.  As with most of us, we work on the Jeep when time allows (unless it is your daily driver and you HAVE to get it fixed so you can get to work tomorrow).  After it is painted and installed, we will start plumbing the compressor to the tank and up to the air manifold (which we have yet to make).  Mike will pick up the appropriate sized electrical wire to provide power to the compressor as well as a power relay and fuse/circuit breaker.

ExtremeAire OBA

A couple of weeks had gone by since Mike and I worked on his OBA setup.  During that time, he painted the rack and ordered a few project parts from an on-line  store.  When they arrived, I headed over to his place to see if we could make some more progress.

Mike decided to use a Maxi fuse for the main power feed to the ExtremeAire compressor.  The holder was obtained and a 60 amp fuse was found at the local ACE hardware store (it never ceases to amaze me as to the variety of “stuff” that store carries).  We put terminal lugs on the 8 gauge pigtails and made it ready for installation between the positive terminal of the battery and the control solenoid.

You can see a portion of the control solenoid in the above picture.  8 gauge audio amp power cable connected the output terminal of the control solenoid to the positive power lead of the compressor.  A butt splice was used to connect the leads at the compressor.  The negative lead of the compressor motor was connected to one of the nearby mounting fasteners using a crimp on ring terminal.  The chassis ground for the negative lead worked just fine, as we later confirmed.  The control solenoid was mounted on the passenger front fender well, about 6 inches from the battery.  This location allowed the Maxi fuse holder to be used without the need of splicing an extension to the holder’s leads.



Mike had a spare ARB pressure switch which he pressed into service when he realized that the one he had ordered had yet to arrive.  A “T” was put in one of the 1/4″ NPT bungs on the tank and to it was connected the ARB pressure switch and a 150 PSI pop-off safety valve.  The safety valve will automatically open and release tank pressure should the pressure switch malfunction and not turn off the control solenoid when the 105 PSI upper regulator limit is reached.  Before wrapping it up, we put some heat shrink tubing on the pressure switch’s electrical connectors.  You would not want those +12V terminals exposed even though the solenoid control circuit is protected with its own 15 amp fuse.  The remainder of the control solenoid circuit is a dash mounted power switch.  When the dash switch is turned on, tank pressure is controlled completely by the pressure switch.  When turned off, the solenoid will not energize and the compressor will not maintain tank pressure.

3/8″ soft copper line was used to connect the compressor to the tank.  It was decided to put a few coils in the line to help dissipate the heat that is generated by compressing the air.  I thought it was a great idea since it is about the prefect size to heat a can of soup.  (I wonder how many tires have to be filled before the soup is ready?)  We found that the fire extinguisher made a good form on which to bend the copper line.  90 degree compression fitting were used on the copper line at the output of the compressor and the inlet of the 1 gallon tank. 

Just in case anyone is wondering, the mounting rack as designed is more than strong enough to hold the compressor and tank in position.  We used large fender washers inside the wheel well where the 5/16″ fasteners secure the rack.  Nyloc nuts were used to help ensure things did not vibrate apart.  Once we had tightened the mounting bolts, we found that we could rock the vehicl side to side by pulling on the rack.  Yep, it was not going anywhere.  A friend of mine was concerned that the 3/16″ strap would not be up to the task.  I believe he will change his mind once he sees it first hand.  (You can see the second bracket that Mike added, under the compressor.)

Once the air line quick disconnect is screwed into the tank, this part of the project will be done.  I asked a friend of mine to bore a hole through the middle of some 1″  aluminum round stock.  The plan is to use a 6″ long piece, drilled and tapped for the appropriate fittings, as an air manifold for the ARB compressor solenoids.  This will allow Mike to use the ARB compressor or the ExtremeAire as a pressure source for his ARB lockers.  Switching between the two will be as easy as moving the quick disconnect from one compressor to the other.

When we get that part finished, I’ll snap a few pics and include them in this write-up so I can call this done.

ExtremeAire OBA

Another Saturday rolled around and Mike and I got together to finish up his OBA project. 

Here is an updated picture of the compressor and tank.  Mike installed a quick disconnect air coupler for the hose he uses to fill his tires.  You can also see the black 3/8″ hose attached to the end of the tank.  It exits the interior of the TJ via an existing rubber plug (now with a .65″ hole in it) in the floor of the tub and runs to the engine compartment,  taking the same route as the gas and brake lines do along the side of the frame. 

While the major purpose of this new OBA setup was to provide Mike with a good air up source for his 35″ tires, he also wanted it to function as a backup to his ARB compressor for operating his air lockers.  This meant he needed an easy way to switch between air sources, a plug and play kind of solution, while on the trail.  While Mike has not had any problems with his ARB compressor, we both agreed that passing up the opportunity for a backup air supply was just asking for Mr. Murphy to pay a visit on the trail some day.  With that in mind, we worked out a 10 second solution to switch between both air sources.

Both Mike and I had some air manifolds drilled for this project.  I had a pair made from 1″ aluminum round stock and Mike had a pair made from rectangular stock.  When we got together, we exchanged manifolds and Mike decided to use the one he brought as it was easier to mount.  Unfortunately, it had been tapped for 3/8″ NPT fittings at each end which he hadn’t counted on.  (He assumed it was going to be tapped for 1/4″.)  No biggie….a spare 3/8″ hose barb was put into use and it worked just fine.


The 25′ length of 3/8″ Goodyear air hose that Mike had was more than long enough to reach from the air tank (in the back of the TJ) to the engine compartment.  He cut off a 2′ length and attached a quick disconnect air coupler (the same type that the ARB compressor can be fitted with).  A 3/8″ hose barb was screwed into the air manifold and the 2′ hose was attached to it.  The air manifold had been constructed with 4 holes drilled through it to facilitate mounting.  The air ports included a pair of 3/8″ NPTs that were located at each end, a pair of 1/8″ NPTs, and a single 1/4″ NPT port. 


A plug was inserted into the 1/4″ port (it was intended to be a spare).  The ARB solenoids were removed from the ARB compressor and installed in their new locations, either side of the unused 1/4″ port..

It should be noted here that the ARB solenoids do NOT use a common 1/8″ NPT fitting but rather a 1/8″ BSPT fitting.  The major difference between the two is that one has a thread count of 27 TPI while the other is 28 TPI.  Depending on who you talk to, some say you can put a regular 1/8″ NPT into the BSPT tapped hole and there won’t be any problems while others say it will leak.  Mike opted to do it the conservative way and purchased a couple of 1/8″ NPT to 1/8″ BSPT fittings (male to male coupler) from McMaster-Carr’s on-line catalog, just to be safe. 

The 3/8″ Goodyear hose was secured in the engine compartment with some cable ties and a female air coupler was attached to the end of the hose.  Mike plugged the holes in the ARB compressor with the 1/8″ BSPT (you did keep the ones that came in the compressor, right?) plugs.  Since his ARB compressor has the optional tire fill air coupling on it, the hose on the new air manifold will be snapped into this air coupler for normal operation.  If a problem should arise with the ARB compressor, he can simply disco the 2′ hose from the ARB compressor and snap it into the Goodyear hose air coupler.  The ExtremeAire compressor and tank will then supply the ARB air lockers with air.  It was for this reason that Mike used an ARB pressure switch to control the ExtremeAire compressor.  The air lockers will never know the difference. 

Once back home, Mike did a quick leak test on the system using the ExtremeAire as the source.  He filled the tank and cycled the air lockers about 10 times.  He then turned the power switch off and waited 20 minutes before turning it back on.  The compressor did not start up which means the tank had NOT leaked down enough for the pressure switch to turn on the compressor.  He had sent me an e-mail with this info and said he was going to check it in an hour or two and to if it the compressor would start.

Well, that is about it.  Like Mike said, this project is DONE!   I hope this has given you some insight in to yet another way by which you can install your own OBA system from pieces and parts.  Good trails and remember to TREAD Lightly!