dboyte wrote:...thought I would post a reply to tell you just how bad this problem can be. I own a 2002 ZR5 crew cab and have had the problem with the vacuum actuator no the transfer case and a/c switch control problems. The actual problem is the vacuum actuator on the transfer case can and will rupture. This happened on my truck and after several attempts to fix the a/c controls they found the leak and fluid in the lines/dash. The problem gets worse, week after the repairs were done, the truck malfunctioned again on the interstate. This time the vacuum/fluid leak problem caused my truck to jump into 4WD in 5 o'clock traffic. ... It totally screwed up my truck. ...currently in a lawsuit with GMC over this safety defect. GMC is aware of this problem but will not do anything about it. ... it can be dangerous.
OK, I am not so rushed now and have had time to think about this post a little.
I am going to side with GM after reading the limited information that I have from the above post.
There is indeed a problem with the HVAC getting DextronIII in to the vacuum lines when the seals in the transfercase's front axle vacuum switch fail.
However this will not engage the transfercase. The transfercase is controlled by the encoder motor. I do not believe that there is any way a failure of that switch could engage "4wd".
Now I realize that you may be confusing front axle engagement with "4wd" or engaging the transfercase. I find it very unlikely that fluid in the vacuum system would cause the front axle to engage, but I suppose a failure of the switch could possibly do so.
The front axle needs vacuum to engage. It is much more likely that it would not engage if a problem exists, since the default is to the open position.
OK, let's say for some reason either the front axle actuator was stuck , or it did indeed manage to be activated. Where is the safety problem? Yes it may handle differently, but it is more of a concern for accelerated tire wear than personal safety.
There are many vehicles that travel the roads every day that are this way. Chevrolet fullsize in the late seventies through the eighties has a front axle without hubs or an axle disconnect. I relies on the open front differential for differences on wheel speed during a turn. The front driveshaft spins all the time. Most people install lockable hubs to lengthen the life of the spinning parts , and promote better mileage, not for better handling in a turn.
You may indeed feel it is a safety concern. I feel that it is no different than a tire that is low on air. Safety concern, yes. Repairable, yes. Warranting a law suit, no. A tire low on air is much more of a danger, and there is no way that GM can be blamed for that either. Stuff happens.
It does sound like they did have your truck for a long time, and for that I am sorry, but if that is what it takes to have it fixed right, so be it. As long as your inconvenience was compensated with the use of a vehicle during that time, I would not have a problem and that is an issue to be delt with during the inconvenience, not after the fact in a lawsuit.
I don't think pushing for a recall of this transfercase switch is warranted based on safety issues. I don't think those "safety" issues exist. I do feel that a replacement of all affected or "infected" parts is the right answer and that does get quite involved, taking a long time to replace them all.
Summary: I do not see a safety issue here. If you are looking for a "way out" check the lemon laws for your state. If it qualifies seek satisfaction that way.
If you are happy with the vehicle otherwise, have confidence that the problem is fixed and should no longer be an issue.
so finally the other day i was driving and had enough and demanded they check into ut and sure enough somethings screwed up. i dont know the technical details of it but it sounded bad and like it should have been noticed earlier so basically i was right and they are idiots. they said something about fluid in the venst and the t case line is connected to it and leaked or something. i really couldnt tell ya but something like that. anyway they said it hapened to someone else and it was a 1200 dollar bill...thank god fr warranty on this one! but i just thought it was funny because when i first bought my truck it was doing it slightly and over the last 2 years has gotten worse and worse so just shows something small can eventually become a big issue. 
