Transfer Case Noise.

andyems · April 6, 2010

Posted this in the "Ask GM Technicican" Forum and got a few ideas, but thought I'd throw it out here too in case someone here has any more ideas.

Hopefully someone can explain how this Auto 4wd system works. I seem to have a weird noise occasionally when I use AUTO in my GMT900 Silverado 1500. I don't know if I have the 246 or 249 Tcase, I looked in the glovebox and didn't see either of those numbers on the build codes.

I have a GMT 900 Silverado 1500 with the electric dial transfer case with auto. I have noticed that sometimes after I have been in and out of Auto or 4wd at highway speeds, when I turn off the ignition I hear the transfer case cycling/clicking.

For example, tonight I had to use Auto for a short distance at highway speeds and it seemed to go in fine, heard and felt the "clunk" as it went in, and it seemed to come back out into 2wd fine, didn't notice any issues, sounds when turning into the driveway when I got home like it was still in Auto. Lights on 4wd dial show correctly for 2wd, auto, 4wd, etc. When I turned off the ignition, with the knob already back in 2wd, I heard the transfer case clicking like it was trying to come out of auto again. Don't know if this is normal for these transfer cases or not. Thought once you go in and out at highway speed it has to do that normally to maybe reset or something? Also I hear some clicking coming from the Tcase as I'm driving while in Auto like the servos are clicking.

If I'm setting still in the driveway, not moving, motor off, and I turn the knob I can hear the transfer case working in and out of Auto, 4wd, back to 2wd etc. and I turn off the igniton, then it doesn't do it.

Seems to only do it when I am actually driving and I go out and back in to 2wd. And then it seems to come out fine, I never notice any noise or tire hop etc on the road, but when I turn off the ignition I can hear the transfer case cycling or clicking. Tonight I used Auto about 45 minutes before I got home, and when I turned off the truck, I opened the door and heard the transfer case clicking. I figured that with someone knowing the wiring or how the system works, electric, vacuum, etc of the 4wd switch and system someone might know what is going on or if this is normal or not.

Just hoping that someone could explain how the Tcase works and could offer some insight on if this is normal or not.

Again I already posted this in another forum, but am just trying to get ideas before I drive over ahour to the dealer and waste a whole day doing that. Thanks again to everyone in advance for the help.