i have a 2002 z71 and when i put it in 4wd the switch lights up like it should. I can feel the front end pulling when i make tight turns like you usualy can in 4wd. But once i get into mud or theres any resistance to the front tires they dont seem to help at all. it doesnt make any sense to me, i know the 4wd is locked in but why wouldnt it work under a load? Any ideas?

 

Are you sure the front doesn't spin in the mud, or do you just think it should do better? Have you had someone look to see if it spins the front?

 

well my friends said the front wheels werent spinning when i went through some mud, then i was at a friends house and i was backing up his driveway which is a gravel road that goes uphill. locked it into 4wd. The back wheels started digging in and spinning, i looked out my window and neither of my front wheels were moving at all. But today i was out playing in some mud and it seemed like it was working fine, so i dont know whats going on with it

 

maybe a short in the wires? was it wet out when you tried it then today it was dry out?

 

Check the 4WD actuator. Problem with these IFS systems is you have to rely on electronics and actuators to engage the front axles instead of solid front axles that you manually locked the hubs on.
What happens is you press a button or turn a **** (unless you are one of the few lucky people who still have a floor shifter... my 01 2500HD did) which activates the actuator that extends into place and engages a shift fork inside the tranfer case that locks the axles. Most common occurance is the actuator fails to engage or that it's not able to lock the axles.
Try jacking up one side of the front end. Then turn the key to on(but dont start it) put it in 4hi. Try to spin the tire in the air. The drive shaft should not turn nor the wheel. If the wheel does then maybe the acuator is not engaging.

 

does this truck have an auto 4wd selection on the switch? if so I believe that the transfer case actually has a clutch in it.

 

is your service 4wd message on?

 

well its defiantly working. got one of those joyous midnight "im stuck" phone calls. Pulled out a blazer sitting on its axles and an f-150 that was sitting on the bumper. 4wd defiantly worked. I still don't understand the incident on the gravel road hill, but i was throwin' mud everywhere when i pulled these two kids out, so i know for sure now its working.

 

could have been in a bind..or it didnt lock into 4wd.. i always back up after i put it in 4wd then pull forward a lil to make sure.. then when i take it out i back up again.

 

I am currently having this exact same problem with my 96 z71 but mine hasn't started working again