> Tech > Modifications > On-Board Air System

Air on Demand
Adding an onboard air system to the Dodge Ram

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Air horns, ARB lockers, tire inflation, even a small blow gun to remove dust can quickly overwhelm most automotive air compressors. An engine driven air compressor such as a converted York AC compressor can produce large volumes of compressed air, but trying to squeeze one into the already crammed engine compartment of a diesel Ram was not going to be fun. The only available location beside the alternator would make oil changes impossible for the contortionally challenged.  PTO driven compressors were too expensive to be justified by the volume of air I needed.

Air Compressor:

After much searching on the web, a 100 PSI continuous duty 12V compressor became the only choice. This Thomas Pumps air compressor uses a 1/3hp DC motor to flow almost 1 cfm at 100psi, far above what many of the compressors sold for 4X4 use are capable of producing. Obtaining the compressor was another matter. At $500 per unit, there was not much demand for it, and no local shops had a source. On August 30, 1999 a phone call to Dominion Air in Roanoke VA brought good news, they had a source and would order the compressor for me. Expected delivery time: 1 week.
(Note: This compressor is available from Grainger as #5Z678 - Thomas Pneumotive TA-4101-DC)

Thomas TA-4101 DC   Specs and Dimensions

One week later, a phone call - the compressor had arrived. I took off early from work to drive into the city to pick it up. Opening the box, I was impressed, the unit was heavy duty and appeared to be well made. We processed the paperwork and, as I was picking up the box to leave, I noticed the electrical terminal on the end of the motor did not quite look right. Sometime during shipping the box had been dropped on its end, and the terminal had been punched back into the housing. The brush assembly was also damage by the terminal, and Barry at Dominion said it should be returned. A replacement would only take another week.

A little over a week later, I called Barry and asked if the replacement had arrived. Yes it had, and it looked worse than the first. Another replacement would be there in another week. Two weeks later, we were still trying to get a good compressor. Getting the picture here? Someone at Thomas needs to reevaluate the packing system.

An intact pump finally arrived and was eventually installed under the utility bed just behind the cab. Some salvaged Kindorf strut was used for the mounting platform.

Close-up of the mounted compressor. The compressor could be mounted under an OEM bed in a similar fashion.
View from the back looking toward the transfer case
View from under cab looking back toward rear axle. The air pressure switch is just visible in the top left of the photo.
A simple sheet metal shroud protects the compressor and pressure switch from splashed water, stones, and debris thrown by the tires. For deep fording, a switch inside the cab disables the compressor to prevent water ingestion.

Compressor Performance:

Time to take the system from 0 psi to 100 psi:    130 seconds
Time to take the system from 80 psi to 100 psi:  28 seconds
Time to inflate a 255/85R16 tire from flat to 65 psi:  6.25 minutes.

Air Tank

While it would not be able to inflate a 33" MT in one shot, a small hot dog tank would store enough air to operate the air horns and repeatedly cycle the ARB locker. 4Wheel Parts Wholesalers listed a 2.5 gal tank that would fit under the passenger compartment. Sold by Sun Products, this tank has five 1/4" pipe fittings, and legs which bolt to any flat surface - the floor of the passenger compartment in this case. The seats were removed and the carpet was pulled back to drill the holes and bolt the tank solidly into place.

150 psi rated rank is ideal for air locker setups or running small air tools. Measuring 6" X 24", this tank can be easily mounted alongside or between frame rails. Five 1/4" NPT openings allow mounting in any position. QUI-PA501 2.5 gallon air tank $69.95
The air tank hangs below the passenger's side of the truck cab. The nerf bar provides some protection. One of the optima aux batteries is mounted in the box to the rear of the tank.

Air plumbing

A cutoff valve was installed at the forward end of the tank to permit work on the forward air system without emptying the tank. From there, 90 degree elbows and a 10' long piece of 3/8" air hose carried the air to a manifold mounted behind the front bumper. The manifold, air solenoids, and regulator for the ARB were mounted on a removable plate.

The manifold, air solenoids, pressure regulator for the ARB air locker, and a hose quick coupling were mounted on a removable plate behind the Reunel winch bumper on the driver's side. Another standard quick coupler on the forward end of the air supply hose allows quick removal of the distribution system.

A 35mm film can keeps dirt/H2O out of quick couplings

Originally, I could not find my teflon tape and used teflon pipe dope to seal the fittings. At 100 psi, almost every fitting leaked. All connections were disassembled, cleaned, and teflon taped, ending the leaks. Quick couplings do not always seal well and the system loses about 8 psi per day, but I can live with that. When the truck is parked, the compressor runs about 20 seconds each day. The compressor also runs occasionally at night as the temperature drops.

A standard air compressor pressure switch set to maintain air between 80 psi and 100 psi is mounted beside the compressor. A check valve is mounted at the air tank to prevent backflow into the compressor. The pressure switch has an auxiliary unloader valve to allow easier compressor starting. The end of compressor can be seen to the left of the switch.

The large pieces (hoses, manifold, regulator, quick couplings, air chuck) were obtained at the local Northern Tools in Salem VA. The pressure switch and check valve were purchased at the local CT Farm and Country. The tubing, small fittings, reducers, valves, and plugs were obtained locally from Lowe's Home Improvement and AutoZone Auto Parts.

Note: The tubing fittings included with the air horn had short sleeve inserts which allowed the brass ferrule to tilt and leak after several assembly/disassembly procedures. The fittings from Lowe's included a longer sleeve which stabilizes the ferrule.

Air Attachments Carried:

25' x 1/4" air hose with M male and M female quick coupling ends - with several quick couplings distributed around the truck, a single hose will reach anywhere easily.

Tire inflation chuck - Airing up tires is part of the four wheelers routine.

Compact blow gun - ever drop a part into the dirt and then spent 15 minutes trying to clean it?

Valve with 1 ft hose and two male M barbs - enables filling one air system from another.

Additional Notes:

Time spent on this system installation ( the bulk of the physical installation was completed in one weekend )

Update - July 2000

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This page was edited on: May 3, 2004