Hi - I have a 97 blazer - all lights operate properly on 3 button 4wd switch. Originally found a bad vacuum actuator with broken diaphram. Replaced it and observed both front wheels turning while vehicle on jack stands. After test driving noticed that when in 4hi or 4lo vehicle will produce a loud klunk once in a while - not consistent with any particular speed or rpm.
The sound is sort of like having a bad u-joint. When driving in 2hi the vehicle operates normally, there are no klunking sounds when shifting while parked or while driving.
The problem is only present in 4w drive - just wondering if anyone has experience the same problem.
I've heard of a fork mechanism in the transfer case wearing - just wondering if this would produce the symptoms I've described and how hard it is to repair it.

 

4wd repaired - klunking in 4wd mode eliminated - no assistance required.

 

Glad you got it figured out and sorry that no one responded to you, but could you post what you found that caused your problem? Could help someone else in the future.

 

I am having the same problem with a 98, could you tell me what you did to fix it. Thanks Sulley

 

STOP doing this people!!
When you find& fix your posted problem(s)>> post your solutions<<!!

I say this with annoyance because i have THIS very exact issue..now i have to keep 'searching"..

 

I am having this same issue as well. Any help much appreciated!!

 

I replaced the transfer case, it was a bad chain. Sulley

 

that isnt the news i wanted to hear lol. glad you got yours fixed.

edit - mine is the same issue. chain is skipping teeth inside the TC. being replaced today

 

TC was replaced on Friday. Noise is gone, 4X4 works great! off to the trails and bring on the snow!!