I don't know if this has been covered, but I have (I think) a unique situation here...
I bought this car from someone in Alabama, and they were and elderly couple, so they never abused it, said it had never been off-road, and thus they never used the 4x4 feature on this Blazer. Well, I live in Vermont, and I tested the 4Lo and 4Hi the day I bought it and it all worked great.
However, after I performed my most recent oil change, and added a new water pump/cooler, my 4x4 is very sketchy...

When I'm stopped, in N, I can shift into 4Lo no problem. Once in 4Lo, I push the 4Hi button and I can hear the T-Case whirring and locking, and then both lights for 4Hi and 4Lo turn on, and I believe that this puts my Blazer in 4Hi, due to the lower RPMs... However, my truck will not shift directly in 4Hi, you must hit 4Lo first.

Does this sound wierd or is that just me? I'm pretty mechanically capable but I don't just want to take apart my T-Case haphazardly... if I know exactly what to do under there I'll be fine... Any tips or suggestions?

And in case the question comes up, yes, I do do mild off-roading. I like to play in the mud and I'm usually fine in 2Hi for that. I've never had to put my truck in 4WD to get out of the mud. But I do need this 4WD issue fixed before the up coming Vermont winter...

 

how many miles are on it? also if the vehicle has never been in 4hi its not going to be used to it so its like breaking in the t-case from brand new try doing a service to it flush the fluids and see what happens after that if it still is acting up then my suggestion would be to drop the t-case out and rebuild it but if its cheaper replace it!

 

sounds more electrical than mechanical. Should be able to ground pin 13 and recieve flash codes on swith. Those switches give problems and the transfer case control module does as well. Best thing to do is make sure transfer case motor is recieving appropiate inputs and then go from there.

 

So, after flushing the tranny with ATF flush, and then refilling it, checking electrical connections, and knocking on it a little bit (my mechanic said to try it, it worked on his...)
I've arrived at the conclusion that I just need my t-case fixed. I have my best friend's dad who will do the work for free, and he is a GM Goodwrench mechanic, he writes for High Performance Pontiac. But just so that I KNOW what's going on kind of, can anyone tell me what they think is wrong? A quick synopsis of my problem is:
- Electronic t-case will shift into 4LO no problem
- once in 4LO, if you push 4LO, it will shift out of 4LO
- in 4LO, if you push 4HI, both light will come on, sometimes (75% of the time) shift into 4HI, while both lights remain on.

Any ideas?

 

I am kinda curious are you following the instructions of how to shift your transfercase to a the absolute? I am not trying to insult you I am simply wondering, because from what I have been told (I am assuming yours is like mine on the dash switch 2Hi, 4Hi and then 4Lo) that some of these not all that are setup like this are finiky. Meaning likeon mine when in 2wdit will shift fine into 4 Hi like normal at a reasonable speed I never do it higher than 20(justme though with the mileage I try doitas easy on the truck as possible). Now on with the 4Lo problems. The instruction book I think says to be rolling below 5 mph. (I am not 100% sure though, its been along time since I read the book). It also says you can be stop but you will have better results moving. I had the same type of problem (lights blinking wouldn't fully engauge). Now heres what I do, I never go straight to 4Lo from 2Hi. I get in 4Hi first (The way I see it if you need 4Lo you should aready have been in 4 Hi with no success), then while I am rolling (crawling barely moving, just enough for a smooth engaugement). I bumpthe truck into neutral and hit the 4Lo button, then after the light stops blinking I put it back into gear. Make sure you go to D, I tried reverse once and it ground (it was an accident). Same step just backwards for going out of 4Lo to 4Hi. I not sure on this either but I think the book also recommends that you never go straight to 4Lo and you really should never have to if you are wheeling chances are you are already in 4Hi. No I have got mine into 4Lo from 4Hi at a dead stop put into N and reved the engine slightly once and as soon as the rpms come down hit the button and no grinding. I've seen guys go from 2Hi to 4Lo with out going into 4Hi first. I am sure there are guys on here that will disagree with me but everybody has there own opinion. I figure being easy on my truck with the mileage it has on it is the best way as I am saving to do a major build on mine and I would rather have money for parts and mods as opposed to repairs. Now as far as tearing it a part I have done it one time its not to terrabily hard. As far as tearing it apart I would suggest you at least try this and see if it works it would be easier than removing it. You never know you might get lucky. Hope this help ya. Zach

 

CAPranger4300, im having (by the sounds of what you said) the exact same problem...

i got an oil change, and 2 days later it started acting up on me...

i have a bad vibration off the line, but when i get moving (50 k or so) the vibration is gone. (strange?)

im takin it to a shop on monday, and hopefully they tell me its an easy fix.