Sep 22, 2004
I've been dabbling with a PTO driven On Board Air solution.

With all these fancy JDM's in our world, many of them have Air Conditioning, which consumes vital engine space for an engine driven compressor. As we learn to hate the factory PTO winches and replace them with something else, it leaves behind a tantalizing PTO gear box begging for something good to use it for... On Board Air.

I sourced several Sanden Compressors. They are readily available in the junk yards on 90's vintage jeeps, and they are graciously mounted at the top of the engine bay, making removal super easy.

They can likewise be converted to air compressors with the simple tapping and plugging of the oil drain hole, and then the lower gear box filled with grease to provide lubrication to the bearings.


They have many different styles of heads and outlets. I just chopped off the ports, and tapped the head to 1/4 and 3/8 NPT for outlet and inlet.

The tricky bit was adapting the normally belt/clutch driven compressor to PTO driven. Having surplus factory PTO shaft on hand, I cut the shaft, and used my lathe to bore out part of a factory shaft to sleeve over the shaft of the compressor... It threads onto the end of the compressor shaft, and is secured with a set screw to a flat spot I ground onto the shaft.

The second tricky bit is how to control air pressure in the system on a continuously running compressor. Answer is a Continuous Run Valve, which is used on gas powered compressors. This allows excess air to bypass once a pre-set pressure is achieved. It also includes a blow off valve and check valve. $90 from Acklands Grainger.


Tricky Bit 3 is finding a place to mount the compressor. I ended up reversing the output of the PTO box so the shaft now shoots backwards, and mounted the compressor under the body, mounted to the underside of one of the body cross members...

I did my first test run last night, and at 1800 rpm in 5th gear, the PTO OBA aired up my 37" tire from 0 to 32 PSI in exactly 1 minute.

I dismantled the compressor afterwards to see how it handled the first run up, and it got very hot, and was oxidizing the grease I was using. I will swap out this grease for a high temp grease. I was also gettng a lot of grease blow by, so I will limit the grease under the pistons, and contain the grease within the bearing section. Periodic oiling through the intake might be wise for longevity of the piston walls...

I still need to mount the tank and run the rest of the plumbing but thought I would share some early results.
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Jan 5, 2005
That is an impressive amount of air. Next time try filling a know volume tank so you can figure the actual CFM. I've heard large amounts of CFM but be curious to hear what it actually is. 1 munte for a 37 on that pressure seems like it is really moving some air though.

Very cool.
Sep 7, 2012
Edmonton, Canada, T5E-5R9
That is cool. I had a similar thought, though mine was to mount a York at the front (on the bumper?) since that is where the PTO normally comes out. Again it was just a wild thought, but you have done it. Awesome.
May 15, 2005
So any updates, kind of curious as to how it works on a regular basis? Or did the monster shop take
over all your time? Is it done?
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