New Problem: Whirring/Grinding sounds from front passenger side

So, I have another problem with my '98 Blazer, 4WD.

On the way to work this morning, I hear this whirring/grinding sound coming from the front passenger side wheel. I had this happen about a week ago, and then it disappeared the next day, so I was unable to track it back down. Either way, it popped up again this morning. The sound is the same going forward, turning left or right, and increases in sound with speed (wheel turning) and I am pretty sure it doesn't happen in reverse. I noticed that if I engage 4Hi, the sound disappears and then reappears in 2HI. On the way into work, the sound disappeared again.

On the way to lunch, no sound being made. After lunch, I back out of the parking spot, and then go forward and the sound is back. I try testing whether it has to do with backing up, going left or right, nothing. On the way back to work, the sound disappeared again.

I am thinking something with the 4WD partially engaging, but it is still operational with the push button and they all light up when I press them. Perhaps a faulty vacuum switch or transfer case? Also, would a bad vacuum switch lead to a blown 4WD fuse? I am guessing no, but not sure. Not sure where to look, but I can almost rule out wheel bearing/hub. Any suggestions or ideas?

Check the actuator cable and operation.
This link should help.
http://www.automotiveforums.com/vbulletin/showthread.php?t=572914

So, I have another problem with my '98 Blazer, 4WD.


I am thinking something with the 4WD partially engaging, but it is still operational with the push button and they all light up when I press them. Perhaps a faulty vacuum switch or transfer case?

I would say if its a part time system (3 buttons on the dash), its mostly likely the vacuum switch that is located on top of the transfer case.

If its an AutoTrac system (4 buttons on the dash) it could also be the vacuum switch, but this is located under the hood, on the firewall, as the thread MT linked here.

First off, I would like to thank everybody for the ideas and suggestions. This site has been of great help in diagnosing issues and trying to correct them.

Now, from all of my searching, I was leaning toward the vacuum switch on top of the transfer case. I hoped it would be this as well as this seems to be one of the cheapest parts to replace on the 4WD system. So, this Memorial Day weekend, I spent all of Saturday working on the truck. Replaced the shocks, wired a new ground from the battery to the firewall, and some other misc.

I also replaced the vacuum switch, which after getting it out, did not look like the new one in the package. The steel ball was halfway depressed and I could not get it to move in either direction. So, I replaced it with the new one, and so far, so good. Only time will tell if this was the problem as the grinding/whirring sound was sporatic. However, based on the way the old switch looked compared to the new one, I can almost say with 100% certainity that the switch was not good. I hope this follow-up helps somebody else out with a similar problem. It is a cheap part (~$25) and probably the best place to start if you are having a similar problem. Careful taking it off and putting the new one on!! There isn't a lot of room to work and in the process of getting the old one off, I broke the plastic part where the hoses attach. Thanks everybody.

You are welcome and thanks for posting back how it went.
Glad to hear you getting it fixed.
Good luck
MT.