I have a 2002 z71 silverado with push button 4x4.
All my mechanical buddies and me have been stumped on why my 4x4 does not work. I push the 4 High button with the truck on and in park and the light changes from 2 high to 4 high with no problems, (keep in mind this is all on jack stands with all 4 tires off the ground) when the truck is put into drive the rear wheels spin like they should, the front drive shaft coming off the transfer case spins, and one of the front wheels spin, when I stop the front wheel from spinning the other front wheel spins up, I thought great it looks like its working like how it should, but when I try it out on dirt roads there is 100% no 4x4 drive going on at all, it seems that when on jack stands it looks like it works great, but in practice, nothing, is there something like lockinig hubs that can cause the front wheels to not spin when they have a load on them? I replaced the front diff actuator with a brand new one because it was a cheap start just to see if that was it but I still have the exact same results and as stated above. 4x4 low is actually 2 wd low as it makes the truck barely move and have loads of torque but no 4x4 still. Pls help, thank you for your time

 

The problem is likely in your transfer case. I'm not sure exactly which unit your have (it should be stamped somewhere on the case), but it will be something like worn out shift motor, clutch pack or fluid coupling. Testing the system with all wheels in the air usually isn't an effective test, because the driveline often incorporates some preload. (a certain threshold of torque that needs to be overcome).

First step is to identify the transfer case. Maybe check the condition of the fluid, and wires/connectors (if any)

 

Specs say it should be a New Venture NV-263 transfer case. As to why it won't engage into 4x4, it could be many things.

 

if it's the 263, then take off the external shift motor and hit it with 12V to make sure it works.

 

I will try that once I get the chance