Hi guys, well this happen about 2 weeks ago. I was down at the beach and on the way back at some point doing around 65mph I thought I herd something like a humming noise. Didnt pay much of attention, thought it could be another vehicle next to me doing that. Then I am about to get off the highway and it scared the crap out me. I thought something was rubn in front of the vehicle when I was slowing down, it was loud. It sounded like gears that are not fully enganged to each other noise. I pulled into a parkinglot and looked around everthing seemed to be tight suspension wize. I put it in reverse and D. still did it. Then I pushed the 4x4 on and that was it! No noise... So I continued like that for some time and took it off. 10min later it did again, and engaged the 4x4 and the noise was gone. Ever since that day it has not done that again on Drive. Glitch maybe? Any idea what it might be. Should I worry?

 

Year would be helpful but, more than likely the vacuum switch on the transfer case needs replacement. Over time they leak vacuum past the seal and start to apply partial vacuum to the front axle actuator under the battery. The actuator pulls a cable inside the right front axle tube and engages a clutch which locks the differential to the right front axle. The grinding, humming, noise is the gears partially engaging. Selecting 4WD applies full vacuum to the actuator, the clutch fully engages, and the noise stops.

The switch, Dorman OE Solutions 600-500 - 4WD Switch | O'Reilly Auto Parts is located on the driver side of the transfer case inboard, and slightly above the front drive shaft yoke.



Maybe a 15 minute job to replace it. When you remove the vacuum connector from the switch, make sure there's no fluid in the lines. If there is, let us know and we can explain how to clean it out.

Just an FYI: 4WD should NOT be used under any circumstances, on dry pavement.

 

Sorry about that, its an 02

 

If you go with the Dorman, make sure those plastic prongs fit tightly into the rubber cap thing where the vacuum lines join into. If it's a loose fit, you won't get enough vacuum to engage the 4WD actuator under the battery tray.

Even if no fluid comes out of the vacuum lines, I would still do an easy little spot check and unscrew the fill bolt (top bolt) on the back of the transfer case. If any fluid comes out, that's a leaky input seal where the transfer case and transmission join. Both of my vehicles have had leaks at this seal, which ends up over-filling the transfer case with fluid. When that happens, you increase the odds of t-case fluid pushing its way past the seals on the vacuum switch. When fluid gets in the lines....well, come back here if you have to, and we'll tell you all about it.

 

Thanks guys... I will check into it when it starts up again

 

When you hear it grinding, the clutch gear and axle shaft are being destroyed. Don't wait, or the repair cost will go from $10 to $600 or so, real quick

 

Gotcha!

 

What they said! $10 dollar fix, easy to do if you are a contortionist. I had the exact same problem with mine.

 

That is exactly what I just had to do on my 1998 Blazer. the right front was making a growl noise. My wife said it sounded like an airplane. But pulled the battery checked that part there changed some vacum lines main supply from engine and a coule of small ones that connect to the others making sure that I got them all back in the proper places the climbed underneatht the truck where I could just get my belly under the frame. tried jack it up but the jack wa in the way so let it back down and suffered with just making it under there. and changed that transfer switch making sure that the vacum lines there were good and presto no more noise.