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Hummer Knowledge Base

The Hummer Knowledge Base

Tires & Wheels/CTIS/Leaks:

From what I have heard, the most common cause of leaks is the fitting connecting to the spindle passages. These lines have been replaced in 96 and later, with steel stranded lines. The next most common site of leak is the quick disconnect fitting at the wheels.

Some have mentioned that the Quick connect fittings cannot be disassembled or rebuilt. They can be disassembled and seals can be replaced rather easily --if the parts can be found. The O rings could probably be found at a plumbing supply. These fittings are also recommended to be used on the Cepek wheels since they are better built.

The key to the quick disconnect disassembly is separating the tire valve unit from the spindle unit. This is done by putting the valve section in a vise while putting a vise grip (with cloth to prevent deep cuts) on spindle section turning and pulling outward. Its a press fit.

If leaks still exist, the next step is to tighten the larger compression fittings (3) on the inside tire selector valve.

Next onto inspecting the tire gauge connections and then those hard to reach frame rail connections.

Some steps can be taken to narrow down the location of the problem.

If it is a very fast leak, you might be able to find it by sound. If not, some detective work will be necessary. The following procedure assumes only one leak.

First, identify whether it is only one axle, or both. (For those of us with older Hummers, set the axle selector switch to "off".)

If it is both axles, the leak is somewhere between the axle selector and the compressor.

If it is one axle, release both of the CTIS valves at the hubs. If the guage still shows a leak, it is in the lines between the selector and the hubs. (The guage will show a very rapid leak in this situation.)

If the leak stops, it is most likely one of the valves, or a tire. Re-connect them (one at a time) to determine which one.

If it is one of the hoses, the leak can often be found by squirting a little bit of soapy water on the connections, or suspected leak points.

Dave Breggin
'95 Diesel Wagon

My 96 has been losing air all day. The front air pressure has been going > down all day (about 10 lbs. in 3 hours) but I can not find a leak anywhere. I have checked the tires and there is no holes. It has been cold here around +5 and I was thinking that is has to be coming from the air control valves area. First I noticed that the air gauge for the front did not move at all this morning. Even after taping it a few times. It took a few hours of highway time till it worked the way it should. I have went to the HID and tried a few things (soapy water, listen for a hiss & etc. ) and I am still lost. I did not have a problem with this till the cold weather came. Last winter it worked fine. Could it be that a control valve is frozen partly open? (the valve that allows it to inflate / deflate the front tires).

John Popolo
96 4DR HT N/A (Green)


You might start by inflating the fronts to some standard pressure....say 35 lbs. Check them with a manual air gauge at the access stem on the wheel to be sure they are correct.

Disconnect the wheels from the system at each wheel with the quick-disconnects. Monitor the pressure with the manual gauge at each wheel over a period of time.....maybe overnight. If one tire loses pressure and the other one doesn't, then you've at least narrowed it down to that corner. If neither tire loses any pressure, then you've eliminated any problems from the quick-disconnect outward. The leak will be somewhere from the quick-disconnect inward back toward the valving and the compressor outlet. Just keep eliminating the gets a little harder once you have to start tracing the air lines up into the chassis area.

Be sure to try the 'soapy water in a spray bottle' test on all fittings and connections along the route......and be sure the lines are pressurized when you do this (connect the tires back in line).

Good luck with it.

Rick Crider
Monroe NC

> My CTISystem seems to have a leak somewhere.  It
> only involves the front tires, I've removed the tires
> from the equasion by disconnecting them.  The
> CTISystem always seems to be deflating the front
> tires, not unlike like a small leak.  Probably a 20
> cent o-ring.  My problem is that I am not very
> familiar with the whereabouts of the CTIS and where it
> runs through.  If anyone knows where the deflating
> valve is, this information would be very much useful.
> -Mike

Check the two small hoses that connect the CTIS system to your gauges. They are under the hood, in front of the compressor (to the right of the washer fluid resevoir on the 97). There are two very small hoses that come out and go to the guage. They should be connected with a small ring that hold them in. Try pulling them out and re-seating them. For the front tires, I believe it is the front hose.


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