Serious truck owners know having a supply of compressed air can be a lifesaver. You can pump up giant mud tires before getting on the freeway and have the ability to use air tools to fix all the parts you break on the trails. By mounting a compressor that is driven by the engine under the hood and a storage tank under the bed, you can always have pressurized air on tap. Kilby Enterprises is now offering a kit for your Cummins or Duramax truck that gives you all that, along with a power switch in the cab and quick-connect fittings for both ends of your truck.
This '05 Chevy 2500HD has already been modified for off-roading and long-haul towing. The Kilby onboard air kit comes with an air tank, a compressor, a power switch, an air manifold with pressure gauge, a coalescing filter to keep lubricating oil out of the air lines, quick-connect fittings for the front and rear of the truck, air lines, and brass fittings for all connections. The kit is designed to fit a stock truck, so a few modifications were needed for this 4x4 tow rig, such as a smaller air tank than the one here to fit in the space available next to an auxiliary fuel tank. | 
1. Disconnect the negative battery terminals. Remove the serpentine belt from the engine by loosening the tensioner with a long wrench and a sleeve for maximum leverage. Don't be afraid to ask for help (it's better than explaining how you gave yourself a black eye with a wrench) because you'll need at least one buddy to assist with the install if you want it done in less than half a day. | 
2. Remove the driver-side bolts on the top of the air-conditioning compressor and temporarily mount the air-compressor bracket to check for clearances. This truck has an aftermarket engine programmer and supports a large stereo system that adds lots of wires and inline fuses to the engine bay, so many of the cables had to be rerouted. |
3. Install the clutch assembly onto the compressor and mark the keyway on the clutch housing with some paint so you can tell when the wheel is in a position where the compressor oil can be checked. | 
4. Bolt the mounting bracket to the air compressor before installing it into the engine bay. This is one of the steps where you'll need a buddy so he can hold the compressor level while you bolt it in. This will ensure the vibration of the engine does not loosen it... | 
...The air compressor can be mounted horizontally or vertically. The vertical mounting did not leave enough clearance under the stock hood in this application. |
5. GM uses a six-rib serpentine belt but doesn't use one long enough for this application, so a Ford Power Stroke eight-rib belt is relieved of two ribs. Make sure to know which engine your truck has before you order this kit. In 2005 alone, there are four different stock belt lengths for the LLY Duramax... | 
...This version of the LLY (single alternator with A/C and vacuum pump) requires the installation of some smaller idler pulleys in the accessory drive so the belt will fit properly. | |