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Off Road Enhancements Enhancements to improve your off road travels

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Old 01-07-2006, 06:46 PM   #1 (permalink)
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Do-it-yourself onboard air

Caddy Compressors and Fire Extinguisher Air Tank

Steven (Robinhood150) outlines the procedures he used to modify two cadillac compressors and a fire extinguisher for on-board air.

Having the freedom of going off roading and knowing there is a source of air after the trail is a great feeling. These sources of air include the Powertank, ViaAir air compressor, converting the air conditioning compressor and other various 12V air compressors. However, for those of us who are on a budget and like air conditioning, there aren't a lot of choices for that source of air. Every air compressor that is inexpensive also has a low flow rate, short duty cycle, and will not last long.

Although the caddy air compressors are slow, they are still faster than the cheap Wal-mart specials. 1980's cadillacs used an air ride suspension system and to pressurize the system a 12V air compressor was used. The air compressor can be found on the driver's side of the engine compartment. Be sure to get the mounting brackets too. Some compressors are known to be made with plastic pistons and I'd assume these are on the late 80's caddies. I'd recommend looking for the early 80's models.

First, I obtained two caddy compressors from the junkyard for $20 each. They were a lot smaller than I thought which was good because I still hadn't figured out where to mount them. I took them apart to see how they work and see how I can improve the flow.

Click the image to open in full size.

From my research I found that I could remove the electronic bleed off valve and the desiccant chamber. The electronic bleed off valve allows the cadillac suspension system to release air pressure and the desiccant chamber dries the air before it is released to the system. I didn't need the desiccant chamber because my air tank is stainless steel and should not rust, besides, I'll just empty it a couple times a year.

Once removed, the electronic bleed off valve will leave a hole that needs to be plugged. Also, by removing the desiccant chamber I had opened up a hole that couldn't be used for air hose attachment. To plug these holes I JB welded them shut, as shown in the picture below.

Click the image to open in full size.

However, with the output port plugged, how do I get air to the tires? Well, the best place to attach an air hose is the schraeder valve on the top of the compressor. It's the perfect size for the 1/4 inch ID of the hose, but the ID of the schraeder valve is tiny. I ended up drilling the valve larger to 7/32".

In an attempt to provide the compressors with clean air I loosely stuffed oily foam in the area where the electronic bleed off valve was as shown in the above picture. I then punched out the sheet metal circle on the side of that chamber and sealed the opening on the top plate with aluminum foil as shown in the picture below.

Click the image to open in full size.

Other than general cleaning, that's all I did to the compressors. Now I needed a place to mount and wire them. Not wanting to move anything in the engine compartment I looked under the 4Runner. I found lots of space above the rear axle and to my surprize it was relatively clean, no mud splatters. And as for water crossings, that part of the body is about 8 inches above the bottom of the door sills, so at that point I think I have more things to worry about than getting the compressors wet. Besides, I don't think enough water can get in the compressors to do any damage, it's not like I'm running them while crossing a stream.

So I drilled some holes in the body and screwed them there. I then ran some air hose from the two compressors into a manifold and into the inside of the runner. There I have a length of hose long enough to reach all 4 tires from inside or I can attach my air tank and fill it up.

Click the image to open in full size.

Click the image to open in full size.
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Fire Extinguisher Modification

As for the fire extinguisher air tank mod I got the idea from Roger Brown's website, who in turn stole the idea from somebody else.

Disclaimer: Working with pressure vessels can be dangerous. I cannot guarantee the safety of the following procedures for modification, nor can I guarantee the safety of using a fire extinguisher as an air tank. Use at your own risk.

Roger Brown's air compressor page.


There is a fire extinguisher refilling company around the corner from my work so I walked over there and asked if they could donate a stainless steel water fire extinguisher tank that they had no use for. They said sure and I picked up one for me and one for my friend.


The modifications were really easy. First, I removed the pick up tube on the inside and removed the handle and firing mechanism from the head. Then I drilled out the top (where the firing mechanism is) and tapped the hole with a 1/8 NPT tap. I also chased the hole where the hose was with the 1/8 NPT tap. These two ports are used for the inlet and outlet since they have the most material to work with and don't require too much more drilling. The holes where the gauge and the schraeder valve are have really small ports to the tank, so if you want to use them then you have to drill them out.


Here's a few pictures of the tank:

Click the image to open in full size.

So how long does it take to fill up the tank and fill up the tires?

Well, here's what my tests have shown:

Tank only:
0 PSI - 20 PSI takes 20 sec
0 PSI - 40 PSI takes 40 sec
0 PSI - 100 PSI takes 3 min 45 sec
Tire, (1) 32x11.5 inch Pirelli Scorpion AT :

With the tank filled to 100 PSI and the compressors running it takes 3 mins to fill from 10 PSI to 32 PSI.
Without a tank it takes 5 mins to fill from 10 PSI to 32 PSI.
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Steve. '93 4Runner V6 Auto 4x4
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Sierra Club policy: [A reason to close trails] ...Physical soil damage, often readily visible, resulting in:
a. Erosion, causing soil loss and damage to stream banks, streams, and fish habitat...
Lesson...Stay on the TRAIL!
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Old 01-07-2006, 06:46 PM
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4runner, ac, air, board, cadillac, compressor, diy, engine, extinguisher, fill, fire, mounting, onboard, pictures, tank, yotatech

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