Installing CTIS on a HMMWV

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NOTE: This setup doesn't include any warning lights for low pressure. I recommend that you install a setup like this with beadlocks or modify the system to incorporate a low pressure light / buzzer.

If you don’t have runflats you will want to have your truck on jack-stands when deflating the tires. The weight of the truck can un-seat the tire bead which can be very difficult to get back on without proper equipment.

Parts:

Tools:

First, and probably the most important job is to layout where you want your CTI pump, CTI deflate valve, and other accessories. When I did this conversion on my ’85 M998, I chose to put my CTI pump under the passenger rear seat. All of the AMG produced models have this equipment under the hood, but in that location, over time many people have found there to be issues with their pumps / valves due to exposure to salt, water, mud and sand. In a Humvee, the seat bases are hollow and are generally used for storage.

For the CTI lines (and electrical lines), I decided to route them from that seat base compartment between the frame and body tucked up high enough so that they can’t drag or catch on anything while off-roading. They then went to their respective locations.

The most labor-intensive part of the procedure is to outfit the geared hubs with the CTI ready spindles, or to fully replace the geared hubs. If your desire is to install CTI equipped spindles and steering arm covers, Chuck Kopelson has written an article on how to replace geared hub seals, which shows how a geared hub spindle is replaced (another article to take a look at is Gear Reduction Hubs Also found on this site). If you were to replace the whole geared hub, Chuck has another article showing how to replace springs, tie rods and A arm bushings which shows how the geared hub is removed.

Changing out the geared hubs – Things to watch out for

The difference between a CTI equipped geared hub and a non-CTI equipped geared hub is simply a hole inside the spindle and steering arm cover. The non-CTI geared hub has a sealed spindle and a sealed steering arm cover. The top cover is sealed and the bottom pictured cover is for CTI.

Mounting the Compressor and Valve:

I mounted the valve in the passenger rear seat compartment since it would be out of the elements. The civilian trucks mount these parts under the hood.

Run the Air Lines:

The barbed connectors are screwed into the steering arm covers to accept the air hose. Then, the air lines need to be assembled and run per the drawing below.

The green line in figure 4 comes from the air horn on the engine and supplies filtered air to the CTI Pump. The blue line comes from the CTI pump and sends pressurized air to the CTI selector switch. From the selector switch the air is routed to the front or rear tires. Note: I didn’t show the hoses going to the CTI Gauges, they will be shown later.

Warnings about mounting airlines


Assembling the Electrical Harness

The electrical system for this project is really very simple. Since my system was 24v, on a civilian truck (or a modified HMMWV) this would need to be altered. From the positive battery terminal (positive going to the body harness – NOT the positive that is bridged to the opposite battery) take a wire and run it up to the switch located in the dash. This wire will need to be fused incase of an overload in the circuit. At 12v the system needs a 30 amp fuse. When running at 24v the system needs a 15 amp fuse (V = I*R – Ohms Law). Place this fuse somewhere between the battery and the switch. I prefer the location to be under the dash.

The switch that I used in this project is an actual military DPDT switch. Any switch with the proper current rating will do. The switch has a positive input and two switched outputs (4 wires). With aid of an ohmmeter, I was able to determine which output was the constant on and which was the toggled on (when placed on two terminals, when switched the ohmmeter will jump – similar to when the two probes are touched together). From the constant on, I ran a wire to the positive side of the CTI Pump. The toggled on went to the CTI Deflate valve. The negative side of the pump and the deflate valve can be combined and ran to a common body ground. Since I have established a common body ground on my HMMWV already, I used that point as the ground point for the CTIS.

 


CTIS Switch Wiring Diagram

CTIS Wiring Schematic

When building the CTI harness for a 24v system the standard military wire is sufficient. If you are building a 12v system you need heavier gauge wire. The lines from the switch to the light will match i.e. female to male.

Some Warnings about Wiring Harness Location


CTI Pump & Deflate Valve Layout Description

Note: The one-way check valve must be oriented properly in the line (arrow on the valve) or it will NOT work. The pop-off valve MUST be included otherwise damage to the pump due to high pressure can occur.

CTI Selector Switch

At the back of the CTI Selector switch, there will be one inlet and two outlets. On the outlets, you will need to install a tee. On this tee there will be one barbed fitting accepting the air hose going to the respective system (front or rear) and there will also be a compression fitting to accept a ¼” ID hose that can then be run up to the gauge.

CTI Wheel Lines:


The cheapest way to create the wheel side CTI lines is to use the parts in Chucks article on this website (home made CTI lines). Chuck also sells Cepek quick disconnect lines and hub protectors.

Any Hummer CTIS line will work as long as it is compatible with your particular wheels. You will also need to get some kind of CTI shields to protect the air lines from damage.


HMMWV CTIS Equipped Dash (Note: gauge light is not installed)

Once everything is installed, run the system and check for leaks using a spray bottle with soapy water. If you find leaks tighten up the connection and use some teflon pipe sealer. Be sure to put some miles on your truck before you take it off-road with the new system so you can work out bugs that you don’t want to find while off-road.

Once everything is installed, run the system and check for leaks using a spray bottle with soapy water. If you find leaks tighten up the connection and use some teflon pipe sealer. Be sure to put some miles on your truck before you take it off-road with the new system so you can work out bugs that you don’t want to find while off-road.