So I bought this Blazer ( not trailblazer ) and it was making noise in the front differential. when i was in 2wd it was making this grinding sound and if i engaged the 4x4 it went silent. by the time i got it home it was fine, no 4x4 blinking lights, no noise, but it also was not engaging the front wheels. I removed the battery box, and checked the actuator for vac leaks and it was fine. I checked the cable and it was free and retracted fine. I then drained the oil in the differential and it came out like glitter. I then pulled the whole differential out and dissasembled it to find the gear that engages the front end was stripped bad.


So I had a parts Blazer with the same gear ratio and removed it's differential . I installed it and it was fine, 4x4 shifted right in and out, life was good for a few weeks and then it started making the same noise. I then took it apart and found that this one had started to strip the same gear in the same way.. it was as if the ( collar ) that slides over this gear was not disengaging enough and was just making it skip enough to grind it. I took a file and deburred the gear and put it back together. it was quiet again, 4x4 went in and out without a hiccup. week later going down the interstate I heard the grinding again. I put it in 4x4 and it went away. So here is what i think, somehow the vacuum is seeping passed and is engaging the front end while the transfer case is not engaged making the collar which is not turning but is being pulled into the gear which is turning at highway speed and is causing this gear to shave off the edge of it. that sound about right? any help would be great, i'm really not looking forward to ripping this front end apart again and again. anyone have a vacuum diagram for the 4x4 system on this 2004 Blazer 4 door push button 4x4?

 

I would do the Bravada Axle Swap and get rid of that front axle disconnect.
If you want to keep this version, I would put it in 4wd then pull the battery and pull on the front axle actuator cable, hold it in place, rotate the wheel and see if it totally locks.
Sounds like the front axle actuator is not pulling the cable far enough to totally engaging the shift collar.

Bill

 

If you have the four button controls and you (actually) find the actuator is staying engaged when in 2WD, then the two hoses on the vacuum solenoid on the firewall are probably switched. They have to be correct for the actuator to vent when going into 2WD.

 

If you have the 3 button 4wd, see if the slip shaft is engaged in 2wd...if so, I would change the transfer case vacuum switch...Jerry

 

This is for the three button 4wd.
From the intake manifold you have a hose that goes to a one way valve (usually white). One side goes to the vacuum reservoir located in the drivers side fender under the ABS control module. The other side goes to a TEE. One side of the TEE goes to the wiring harness with a vacuum line in the middle of it. Located next to the Brake Booster. This line goes to the HVAC control module in the cab. The other side of the TEE goes to the Transfer Case Switch located on the Transfer case via a rubber connector that is keyed.
On that connector you have two more hoses. One goes to the front axle actuator under the battery. The other is a vent hose that goes to air. Sometimes this one is tie wrapped to the transmission dipstick.
Hope this helps...

Bill

 

turns out that on the transfer case, there is a screw in vacuum switch with 3 hoses hooked to it. the bottom of it has a ball that pushes up to open the vac lines to the front . apparently over the 220,000 miles it has rusted and would not seal shut allowing the vacuum to build up and pull the 4x4 slowly into gear. wouldnt be a issue but since the transfer case is not engaged only half of the front differential is turning while it is trying to engage. i put in a new switch and everything seems to be ok.

 

you're welcome...