2000 Trailblazer with 4button 236 (with 300k km)

I have a clunk coming from the t-case, its like one per tire rotation, does this at all speeds and only when in 4hi 4lo or auto. Of course in 2wd everything is fine.

My switch does work fine, it flashes and lights up shortly after on what ever to pick - so I think my switch and tccm are good.

Have checked the Vacuum Solenoid and that all seem to be working good the cable moves about 1/2" (but slowy... is that how it should be?) but for testing switched to 4wd, then disconnected it so it won't engage the front - and the clunk is still there.

SO could it be my Encoder Motor? I can hear it moving, it moves a bit going into 4hi and 4low, moves less picking AUTO and when you press 2wd it seems to move a lot - is that normal or is it not engadaging all the way?

Oh forgot to say something the front wheels do grab with the clunk going on... so I think everything is switching on ok.

Or is this the worst and its something inside the t-case? I did check the flud and it was full, kind of a green-clear to me, is this that blue auto track II

I found most of these tips by searching the site, but couldn't find anything about how to tell if the Encoder Motor is bad

 

Did you check the universal joint/CV joint on the forward propeller shaft? Check the forward propeller shaft overall for excessive movement that could indicate things such as worn splines, etc. You might also want to check the run-out.

In the past did you or someone else do any work that would have required removing the forward propeller shaft? If not installed correctly this could cause the shaft to be out of phase...though the primary symptom of this is more of vibration than knocking.

I would also not rule out the front differential/axle assembly as the potential problem spot...unless of course there is no doubt the clunk is coming from the transfer case.

 

Ujoint/CV check - not really but will do a better check, sound is coming from the case so I didn't check them that hard.

After the holidays I my next step is to remove the front shaft and drive it in 4hi just down the driveway - hoping this will tell me if its in the t-case or if the sound is gone, maybe it is the front diff

 

it was the CV joint on the forward propeller shaft - I think... replaced and feels so much better just haven't driven it yet - still working on the oil cooler lines, plus want to change diff oil while I have so much removed.

 

hi I have a 1999 blazer. when I put it in 4low and drive in a straight line there is no noice! as soon as I turn there is a very loud knocking noice from the front!!! it does it in 4hi also but a lot less because there is less torque subjected to the diff's. I saw that my front diff is mounted with rubber mountings and is touching the chassie! could It be that the diff has moved on the tube rubber mounts and causing a knocking noice??? please help!!