I have a 2000 Blazer 4x4 that I bought back in November. Back in early February, I was on a drive when, after about an hour, my truck began making a loud sort of grinding/whining sound. After getting it towed home, I started researching (including these forums), and guessed that it was an issue with the transfer case partially engaging, which I confirmed with a simple test (the whining went away when I engaged 4Hi). I took it to a local garage, where they replaced the actuator cable (they said it was stuck). And that seemed to fix it.

Well, on two separate occasions since (a month ago, and today), I had nearly the same thing happen. Both times, I was driving at about 65mph, and after about 15 minutes, the Blazer started whining again. Then, when I would come to a complete stop soon after, there would be a small "clunk" and the sound would go away. Today's event also added a grinding for a second when I had to accelerate across a busy highway quickly. After the first reoccurrance, I took it back to the same garage, and they were stumped because it wasn't still grinding. Their best guess is either a failing sensor or switch, or a slight vacuum leak somewhere that causes pressure to build at higher speeds (it hasn't happened at speeds under 60mph).

So...anyone have any suggestions? I don't know much about 4x4 systems, as this is my first one. I did notice some grey gease dripping a little from what I think is where the driveshaft goes into the transfer case (the shaft that runs from the back of the transmission forward). I also don't have much extra cash right now for repairs. I am reasonably mechanically inclined so if it's a repair I can do in my driveway with simple tools I'm willing. Thanks.

 

I hope someone speaks up, as I am having a similar issue with the actuator partially engaging on its own. It took a while for me to find the source of the sound. One day I just pushed 4 hi to see what happened and the noise goes away. It may not do it for days, and then It may re-occur several times in one trip.

Mine does not specifically do it at high speeds. Usually but not always it is on de-celleration. It is almost as if there is a weak spring in the actuator, or vacuum is reaching the diaphragm when it should not be.