A New 4wd Issue Not Discussed... Please Help

[ecir]

So I have looked and cannot find my issue in the other topics. I have a 2005 LT Trailblazer 4.3 v6 4WD. When I put the truck in A4WD, 4HI , or 4LO... the selector switch and light both will show that the truck is in 4WD, however there is no power in the front tires. I know because I had a friend on the gas while I was pushing because we got struck in red GA clay... When I put it in 4wd i can hear the sounds of the mechanics doing something but then i get a metal knock, after inspection i find that it is the drive shaft coming into the Tranny but on the Transfer case end knocking. It seems to me like it is trying to connect the two front axles but not actually making the connection to power/turn the front wheels. Do u think this is a problem with the shift acctuator switch or in the transfer case itself or something else. Please Please Help

[blue9q]

Hi, I have been trying to figure out some 4wd problems that I am having, and have learned a couple of things about GM's 4wd drive that might be helpful. You generally have two systems that make up 4WD. The automatic actuator that actually locks in your front axles, and the transfer case that locks in to provide motion to your axles. For instance, older 4wd vehicles would require that you manually lock the wheel hubs at the tire to make the 4wd shift. Your trailblazer should have one button that activates a modulator that locks the hubs in place on the axle. This is usually vacuum controlled, but newer are actually electric. The fact that your wheels don't lock can be something as simple and dirty hub bearings. I have read that dirt and water can cause the hubs to bind up and not engage. You could have a bad acuator. This is about $75 and is easy to replace, but tough to diagnose. The knocking could be the sound of the splined shafts on the axles trying to engage, but aren't being pushed out far enough by the actuator to fully insert into the hubs. Inspection of the hub bearing means removing tires and pulling an oil seal on the hub. it'll cost you the price of a seal, but you can get a good look at the state of your bearings. Anyway, Hopes this helps. I sell auto parts for a living and have been talking to a lot of mechanics and enthusiats at work, and this is the advice they gave me. Good luck.