troverman

For me, the solution seems to be to make sure I'm stopped when I shift from 4WD back into 2WD. I even put the transmission into neutral. No clunk when doing it this way. Shifting into 4WD on the move never has any clunking, just shifting out. No big deal, I can do it while stopped and in neutral. I can check the driveshaft u-joints and play in the front bearings once the snow is gone. The truck plowed snow all day yesterday without issue, so I'm happy.

Guys, I have a 2005 GMC 3500 dump truck with the 6.0L and its 4x4 with the manual floor shifter transfer case. Going from 2WD into 4HI is very smooth and it works well. Going from 4x4HI back to 2WD is different. I pull the lever back into 2WD, and within a second or two the 4x4 indicator lamp inside the instrument cluster goes out and the steering is free (I imagine because the transfer case has just disengaged). But then a few moments later, sometimes a minute or so later, there is a big time clunk and the truck shudders. I'm guessing this is the center axle disconnect disengaging? I am shifting in and out while on the move, but never while I'm pressing the accelerator, always just coasting. Is the CAD failing?

Thanks Txab for the suggestions. I have thought about the body ground straps, although I would expect problems with the blower and radio as well if that were the case. I will look at the one under the truck (cab to frame) and the one under the hood (cab to engine). I may just replace them and the ignition switch and go from there. Neither are terribly expensive. It appears that you are in TX where rust is not an issue...I'm up in NH where they throw the salt down hard every year with all the snow we get. My truck is solid but rusty underneath; the grounds may be pretty corroded.

Update and bump. Apparently nobody has seen this issue before. The truck for the last two days is definitely having erratic behavior...you can drive it 40 minutes and it is perfect, everything is fine. Then abruptly, for no reason, all the warning lights come on, all gauges (except tach and speedo) go to zero, but the truck continues to run perfectly fine. Last night it did that, I drove like that for several miles and pulled over. Shut the truck off, restarted it hoping everything would go back to normal...but instead the entire cluster did not work at all. The truck ran fine, the cluster was backlit, but not one gauge worked at all and the odometer and PRND did not even come on. The one thing in common I have found is that the moment the instruments act up...whether the cluster remains partially working or not working at all, the interior dome light will not work. You cannot turn it on from the switch by the headlights, nor will it come on when you open the door. As soon as the instruments start working again, the light works. Meanwhile, the HVAC and radio have never had a problem. And the gauges may randomly start working again, mid-drive, so its not like once they go off, they remain off until a restart. I'm thinking either a ground or the ignition switch. I had decided the ignition switch couldn't be the problem because of the dome light also not working, but I forgot that they are tied in...if you open the door and then shut the door, the dome light delays for 30 seconds and then shuts off. But if you get in and start the engine, the light goes off instantly.

I pulled the cluster and the connector looked good. Pulled the column shroud and removed ignition switch harness. Connection looked fine but lock tab was slightly broken. Still seemed tight. Reassembled everything and turned on ignition...everything was normal for about 30 seconds (engine off, key in ignition position)...then suddenly all the gauges fell to the zero position. Bizarre. Later I tried again and I have no interior done light, even manually turning on dome light switch. The engine still starts and runs; I have radio and hvac, but cluster is totally dead, all interior switches are no longer backlit. ignition switch? Some master fuse?

So as of yesterday, my 2005 Sierra 3500 with the gas engine started doing something weird with the instruments. While driving down the road, all gauges except the tach and speedo drop to zero, and all warning lights come on. The truck continues to run just fine. If I wiggle the key in the ignition switch, usually the gauges will come back and the warning lights extinguish. Now I'm seeing the amber Key with Padlock symbol staying on at all times though. My truck is a work truck with crank windows, no frills. I had the cluster replaced 3 years ago and all has been fine. I did replace the radio with an aftermarket, but that was two months ago and no problems, no harnesses cut. Could it be the ignition switch? Would it be the tumbler portion or the electric switch portion?