On-Board Air

Sep 1997

Background | Parts | Installation | Cost | Postscript

Background

When I ordered my new axles, with ARB lockers, I decided not to get the ARB compressor. I had wanted to build an on-board air system anyway, so I figured now was the time, and while I was at it, I would make sure that I could drive the lockers as well.

After reading about many other on-board air setups, I drew up a schematic and had a few people look it over. After a few minor changes, I began searching for parts.

Parts

Compressor

I knew from other people's experiences, that a York air compressor would be the heart of the system. This compressor is readily available at most junk yards and is a good, high-volume compressor. It was used on a lot of vehicles from Crysler and Ford. If you can find one still attached to an AMC vehicle, you might even get the right brackets to fit a jeep motor.

I had only seen these in pictures on the Web, but I thought I would know one when I saw it. WRONG! The real thing is about 3X the size I thought it would be.

Here is a page of information that will help you choose the right compressor when you go to a junk yard.

Be sure to test the compressor before you buy it. The pully should turn freely. Hook it up to a battery and make sure the magnetic clutch engages. You should hear it click, and the pully should now turn the pump. While the clutch is engaged, hold your finger over the output and turn the pully. You should feel air pressure build up, and you can hear it when you release you finger.

If you look carefully at the pictures, you will notice that my compressor doesn't look like any of ones described. That is because I bought mine before I learned all the details of how to choose one. Now that I have documented my mistakes and the knowlege that ensued, no one else should have to make the same mistakes. The compressor that I got is a York, but it has a different head that is square. Harold from Ready-Air had never heard of one like it, and he has been working with these things for quite a while. Unfortunately, I was not able to use the adapters that he sells, so I had to make it up as I went along. I finally figured out that a pipe-thread bushing with a garden hose rubber washer in it would seal on the input/output fittings on the compressor.

Tank

There are many ways to go for tanks. Some of the more popular include:

• Nerf-bars or Roll Cage
• CO2 Tanks from soda fountains
• SCUBA Tanks
• Air-Brake Tanks

I chose to use the latter since they are readily available at truck wrecking yards, and they are relatively cheap. I was hoping to find something that was roughly 6" in diameter and 18-20" long, so it would fit next to the gas tank between the frame rails. The closest I found was 7" in diameter and 15" long. I figured that was close enough, so I bought it.

If you go this route, make sure to get the mounting brackes. It makes it much easier to mount than trying to fabricate your own. Also, don't worry about a little surface rust. Mine cleaned up nicely with a wire wheel attached to a drill. Once it was clean, I painted it bright red.

This tank had a stamp on it that rated it to 150 psi. Since I plan to run ~120 psi, this should be just right.

The fittings on these tanks are standard pipe thread, so it is easy to find whatever parts you need.

Hose

I initially bought 50ft. of 3/8" air-tool hose. I found that it was cheaper to buy a 50ft. hose with ends on it than to buy the hose alone in bulk, so that is what I did. By doing it this way, I also get two 1/4" male connectors for free.

The hose I got is sort of a reddish orange and is fairly flexible. It should be easy to route, and it cuts easily with a knife or scisors. For each section I needed, I installed one connector, routed it to its destination, measured, and cut. Then I just installed the other connector and hooked it up. I used female free-spinning connectors for all of my connections to the manifold to make it easy to remove and plug in the field if a line was broken.

Pneumatic Parts

• Pressure Gauge - I got a dash mountable pressure gauge at the truck wrecking yard when I bought the tank. It is for air brakes, and reads from 0-150 psi. I plan to use this in the dash. I got another one that is on the manifold under the hood that makes it easy to test and adjust the system. This one is a high quality 0-200 psi gauge.
• Check Valve - Get one with an unloader port. This works with the pressure switch to release the pressure from the compressor side when it is not being used. This saves the compressor seals and lets it start up under no load.
• Pressure Switch - I got one that comes on at 90 psi and shuts off at 120 psi. It is adjustable, so I set it for 80/120. Make sure to get one that has a port for the unloader connection from the check valve.
• Safety Valve - This is a must! The York can easily put out more pressure than the 150 psi rating of the tank. I got a 150 psi safety valve with the assumption that the tank rating has some safety margin built in. I you want to be more cautious, use one that is rated at 130-140 psi.
• Manifold - These just don't seem to exist unless you have them custom made. I just made mine with pipe fittings (tees, elbows, nipples). I learned the hard way that not all nipples are created equal. (OK, so I knew that a long time ago, but that is another story. ;-) ) I used some cheap ones in places, and I could not get an air-tight connection with them. I finally switched to ones that I got from a compressor supply store that have a hex flange in the middle that makes it easy to tighted (or loosen) since you can get a wrench on them. In addition, I used teflon tape on all connections.
• Quick-connect Couplers - I got two couplers that will be installed on the front and back of the jeep to connect tire hoses and air-tools.
• Regulator - This is required for the ARB connections. The solonoids and lockers do not like any more than 80 psi. Since I did not want to run the rest of my air system that low, I plan to install a regulator between the manifold and the ARB portion of the system. I have not purchased this item yet.

Electrical Parts

• Switches - I got a lighted toggle switch from an auto parts store to use for a master switch. The ARB switches came with the lockers and are push type on/off swithces. I have not yet decided what to use for the gear gift mounted switch.
• Indicator Light - I got a "12V LED" and mount from Radio Shack. It is really just a normal LED with a small resistor attached.
• Wire - I used some 4 strand wire that I had left over from a trailer wiring project.
• Misc - I got an in-line fuse holder and a 20A fuse to supply the power to the system. I also picked up a package of misc. connectors to make it easer to attach everything.

Installation

Compressor

Findind a place for the compressor was the hardest part. Nothing on my 258 is where it should be, so using stock A/C compressor brackets was not an option. With the power steering pump on one side, and the alternator on the other, there was not much space left. I finally found a spot below the alternator.

It was soon obvious that I would have to fabricate my own brackets. Luckily, the 258 has lots of threaded mounting holes that I could attach to. The only material that I had available was carpetry straps. This is basically metal strips that are 1.25" wide and 1/8" thick. It is not as strong as I would like, but it was easy to shape. By using three pieces of it, I was able to support the compressor quite rigidly.

Once in place, I needed a belt to drive it. I had placed it in the same plane with the alternator, to all I needed was a longer belt. To measure, I used a string and ran it through all of the pullies, then marked and measured. Since the alternator is adjustable, I would have some range in the belt lengths that would work. After buying the belt, I could not get it on. It was at least an inch too short. I finally realized that belts are measured at the outside, but my string was down in the pullies. I re-measured with the tape measure around the outside of the pullies and exchanged the belt. It worked perfectly!

Tank

I had hoped to install the tank next to the gas tank between the frame rails like others have suggested. Unfortunately, when I got the tank home and tested the fit, it seemed too large for the area. It fit, but I was not sure if there was enough clearance if the axle went up with full deflection.

I decided to mount it to the firewall right under the battery tray instead. There was pleanty of room, and it would be more accessible for working on it. To attach the brackets, I had to remove the heater unit on the other side of the firewall. Luckily I had just done this a couple of weeks before to fix the heater fan, so it was not as much of a pain this time. (Tank and compressor picture)

Manifold

Since I could not buy a manifold that met my needs, I built one from standard pipe fittings. It took a bit of trial and error, but I finally hit on a design that seems to work well.

I made a piece of metal that fit between two sets of tees and I drilled a hole in the middle of it. I then ran a bolt through from the fender well and used it to clamp the manifold to the inside of the fender.

Air ports

I ran two air lines to air ports (sounds like United or TWA ;-). One on the front grill, and one on the rear next to the license plate. Each has a quick-connect. The one to the front was very close to the air manifold, so it was no big deal. The one on the rear took a little more work. I had to run the line through the frame then across the back. Where ever it entered or exited the frame, I plan to reinforce it with plastic shrouds so it doesn't wear over time and split.

Once I had everthing in place with the air, I started strapping hoses down to keep them from rubbing. In the process of drilling a hole for a zip-tie, I put the drill through one of my hoses. Now I get to find a good hose repair kit to fix it. While I am at it, I will buy a spare so I can make the fix on the trail.

Fill line and tools

I built a device similar to a Quara-flate except that it only handles two tires at a time instead of four. The other difference is that instead of a connector to attach to an air fill hose at the gas station, this one has a quick connect plug to attach to one of the two ports (front/back) on the jeep. With this setup, I can fill up two tire at once by connecting to the on-board air, or deflate two at once by just leaving it unconnected. To make it easy to use, I put a on/off valve on it, and added a gauge to measure the tire pressure. I purchased the gauge from Quara-flate for $9.95 + shipping. It goes from 0-60 PSI in 1 PSI increments and is supposedly very accurate within that range.

I also built a rubber air line with quick connects at each end to use for attaching air tools. I got an impact wrench for $40 at a local pawn show. It is not real powerful with the air volume I can produce, but it is sufficient to remove/replace lug-nuts. I also plan to get an blower nozzle as well.

Electrical

I picked up a lighted switch from an auto parts store to use for the master on/off for the system. I also got an in-line fuse holder and 20A fuse that I put between the switch and the +12V supply. For a supply, I used a tap off my fuse box that is hot only when the ignition is on.

I ran a four wire line from the far left side of the dash through the firewall to the area of the air manifold. One of these provides the connection from the master switch to the the pressure switch. Another taps off the line from the pressure switch to the compressor clutch. This one I ran to a 12V LED that I mounted right above the master switch on the dash so I know when the compressor is engaged. The other two wires go from the ARB switches to the ARB solonoids. The ARB switches are wired so the rear can only get power when the master switch is on, and the front can only get power when the rear is on.

Cost

Postscript

12/1/97 - I am still getting a lot of oil in the air, so I need to add a separator between the compressor and the manifold.

12/10/97 - On the last trail run, someone suggested that I cover the air ports so they don't get filled with mud. For lack of anything else, I covered them with duct tape. Good thing too. They would have been a mess. Last night I found a better solution. I discovered that the cap from a WD-40 can fits perfectly over the quick disconnect. It is snug enough to hold in place without being a pain to take off when needed. I now sport red caps front and rear.