Hello all. I know this has been discussed several times for newer blazers. I have not seen any posts for pre-2000 blazers. I may of just overlooked them though.

My 97 Blazer has the 3 button 4wd switch on the dash and drives great in 2wd. But when I push either the 4hi or 4lo it makes a clunking sound when accelerating and while cornering. Could the 4wd vacuum actuator be a possible cause of this noise by not fully engaging the 4wd? Or is it something else more expensive?

Any help will be greatly appreciated. I have put off fixing this for about 2 years now. thankfully I have not had to use the 4wd in that time. But this year I am going to have to.

 

have you checked the u joints on the front shaft going to front diff from transfer case?
could be the source..similar to when rear shaft is going out and you get a "clunk" on take off.....my first thought.

 

Yes I have checked the u joints on the front shaft. They feel like they are good but I guess ya never know. It does not sound like a u joint noise though. this is a very loud clunking sound. It almost sounds like someone taking a sledge hammer and hitting the frame of the truck. It's that loud.

 

turn the shaft see if the clunk is coming from the tcase its self

My dads s10 has the same problem i still didn't check it yet but every time i turn the shaft i got a clunk in the t case Im guessing the shaft yoke is bad on my dads pickup 4wd works but i get the clunk noise like you do

 

I'll have to see if I can get some time this weekend and do some testing to see where it is coming from exactly.