I tried a search but could not find exactly what I need. I have a 1992 K1500 Blazer with the manual transfer case lever on the floor. When engaging 4H, the transfer case engages (I verified but trying to turn the front driveshaft by hand in Park, won't turn until shifted back to 2H) but the front differential doesn't engage the drive axles. Also checked the 25amp fuse for the 4x4 - it's fine. Any ideas on what to look for or what may be wrong? My Haynes manual was of no help either.

I did find this thread below describing the same problem I have, but the thread never reached a conclusion. Would appreciate any help. Thanks.
https://blazerforum.com/m_180343/tm.htm

 

Same thing applies. Test the wires at the front diff actuator to make sure that it is getting power. If it is, then the actuator is bad. It is a common thing for the electro-magnet or thermal type actuators. The stepper motor type is much more reliable.

 

this is gonna sound crazy but disconnect your battery for 30 minutes and re connect it. Same exact thing happened to my 1995 blazer and i did it today. My transfer case worked too, and I coulden't figure out the problem. Now 4x4 works like its brand new. I guess your sensors get all whacked out sometimes and disconnecting the battery resets it.
Give it a shot and let me know how if it worked.

 

Well, I finally crawled under there. I am getting power to the actuator, so as Swartlkk mentioned above, I suspect a bad actuator. AZ has a replacement for $69; I'll get one in the morning and see if that works.

 

If you can get the updated stepper motor design, you will not have this problem again! It takes some wiring work, but it is definitely worth it.

 

Thanks, Kyle. I'll see if I can find one locally...

 

Well, I went out this morning to find a replacement actuator. Could not find the stepper motor version in stock as Kyle suggested, so for expediency-sake I just picked up a new OE electro-magnetic actuator at the parts store - around $75. I included a pic below, for those wanting to know. It's shaped like a large O2 sensor. It is a simple screw-on and plug-in process, takes all of 5 minutes. Started up the Blazer, and voila - that solved my problem. 4x4 is now working again.

Thanks guys for the helpful hints on this board.

 

Here's a better pic:

 

Wow... Large pic for something so small! LOL

Anyway, when I was down at my dads house today, I saw an old stepper motor front axle actuator sitting on the shelf. It was cracked and water had gotten inside it shorting things out. Dad beats the crap out of his trucks! Anyway, I grabbed it and will snap some pictures of the plug and the whole unit for anyone interested to have a look at.

*EDIT* - Here's the guts of the upgraded stepper motor actuator for the IFS fullsize trucks:
It has a gear reduction drive between the stepper motor & the threaded rod that drives the piston out to engaged the front axle so it's stronger than all heck (provided the threads on the threaded rod don't strip):

It incorporates an encoder to keep track of the number of rotations of the output shaft:



I mention the threads stripping because that is what finally did in the actuator I disassembled as you can see in the picture below:

This is the weakest point of this actuator, but it is far and away a more reliable design than the thermal or electro-magnetic design which predated it.

 

Ouch..yea, I know. [:@] I messed with this picture for longer than it took me to replace the part. Still don't know why the pic came out some #$@&^@ big! Anyway, post a pic of the stepper motor if you geta chance.