Sorry for the dumb question but, i have an issue with the front drivetrain. i have a loud clicking noise in the front so i thought it was the gear that engage 4x4 in the front diff. and changed it but the awful noise is still there but only when in 4x4, in 4x2 no noise at all...so my question is does the front cv axle turn when in 4x2, or is the hub free? i want to know if its ''auto-locking'' or something before i replace the hole axle assy...

realy need help. video down below

Thanx!

 

The front axles are always engaged with the hubs, there is no disconnect. At least with the US version. May have different options on the other side of the pond where they use 6 lug style hubs...

 

So if its always engaged then if its the axle i should hear the noise in 4x2? Here is a video (dont forget it only does this when 4x4 is ENGAGED)

 

The front axle engagement is via a sliding gear that couples the right side of the front axle to the right side CV axle. There is no such engagement on the left side. With the transfer case disengaged, and the sliding gear disengaged, the front wheels can turn independently with the right wheel and CV axle turning together independent of the front differential, the left wheel and left CV axle turning and connected with the front differential, and the front differential not connected with the transfer case. (I only really dove into this topic recently when trying to find out what seals went where on my front axle so don't count me as much of an expert.)

Here is a link that describes how this axles work: https://www.s10forum.com/forum/f220/...nt-end-506164/

BTW: What year Blazer do you have? I could tell from the video it is a second generation with a 4-button controlled transfer case.

I noticed that the noise only occurs when the wheels are turning fast enough and when you slow down the sound goes away. When turning fast enough, the frequency of the clicks follows the wheel speed. This is a total shot in the dark but could there be something loose that is attached to something that only spins when the 4wd is engaged? This loose thing would be thrown outward when spinning fast enough and then hitting something when the wheels or drivetrain are going sufficient speed,

 

Its a 2002 LS 4dr with the 4wd Auto yes... Good point, ive checked on both sides if there was something loose like you said but everything looks fine sooo i thought maybe the spines at the ends of the axle that are striped or something, or maybe u-joints?

 

Input shaft to front differential??

 

It's not the U-joint. They would knock while start/stop. While constant acceleration the noise should go off. And yes, the axles always turn, no matter if You're on 2WD or 4WD. It's not the axle.
From what You say it looks that there is something wrong with Your front diff or a front diff engagement actuator/cable. Did You check the diff oil level?