Please bear with me, I've been browsing the endless 4x4 problems on here for about three hours to try and avoid annoying everyone with another thread on 4x4 problems, and still can not find exactly my symptoms described. Maybe someone will just know my problem right away and can help me get this over with!

SO. I have a 2000 4-door LT Blazer with the 4-button 4x4 (auto 4x4, 2hi, 4hi, 4lo) and just hit 170,000 miles. Around 130,000 miles, 4x4 was starting to take forever to engage. I would push 4hi (or 4lo or auto) and it would take up to 45 minutes of blinking until it engaged. Would switch back to 2hi immediately upon request. I found that there was a vacuum leak from the actuator to the firewall nipple thing, so I replaced the vacuum lines and and actuator for good measure. I also changed the transfer case oil. So for the first time, around 160,000 miles, i got it to FINALLY engage 4x4 one day, and then took a tight right turn and CLUNK, it was back in 2wd. By clunk I mean, as if you were moving in reverse at 10mph and threw it in drive. That sort of a "my drivetrain hates me" clunk. Pretty sure that it only does this when turning hard right, but it acts close to doing it when turning left as well. The steering wheel gets tight and harder to turn while in 4x4 (this has gotten progressively worse over the last year or so), and then CLUNK and it's back in 2wd. So a couple times since then I got stuck, and screwed around with waiting a couple hours for it to engage 4x4 so I could get out of the mud. One night, I pushed 4hi and then it was just going back and forth between 4hi and 2hi, about every 5-10 seconds, smoothly, and while driving mostly in a straight line for about 30 minutes. As of yesterday, I left the 4hi light blinking all day as I drove 500 miles and it never engaged. As of yesterday, sometimes when I start the engine the "service 4wd" light is on, and sometimes it isn't. Another detail is that gravel roads would almost always get it to engage into 4x4. All of the sharp rapid bumps for some reason would do it. No other kind of bumpy road. No combination of drive, reverse, neutral, 1, 2, 3, 2hi, 4hi, auto 4x4 or 4lo, or turning different ways, or driving on different terrains, will get it to engage 4x4 now....

 

Maybe just a link to a thread that should help? Like I said I've spent hours to no avail browsing 4x4 problem threads trying to find one that helps me.

 

did you see the one about most common 4wd problems thread?
although it sounds like you've already replaced quite a bit

also are you getting the actuator and the vac resvoir mixed up? the resvoir is in the fender assembly and the actuator should be under the battery(depends on what year blazer )

 

It was the actuator under the battery that I replaced, but I think the old one was fine too. Yeah, I've been looking at that thread and another one that's really informative (https://blazerforum.com/forum/tech-articles-diy-29/4x4-no-worky-maybe-will-help-7180/), but I'm still having trouble finding my Blazer's symptoms described anywhere. Doesn't sound like it's the switch on the transfer case...but maybe I'll just replace that too.

 

have you checked the tccm located behind the glove box

 

Haven't checked it, but it clicks when you push 4hi or 4lo. I think I've read that clicking doesn't necessarily mean it works completely...but...