The blazer, s10, etc used the vacuum actuator through at least 2001. Mike, call me and I will quickly walk you through the venr vacuume leak issue that causes the S10/ Blazer 4wd not to engage.

i was thinking i maybe only half right on the full size using actuators for the hvac. i know they used them for temp, but when my old mans truck was acting up and i was looking up parts it showed a actuator for position too but that may only be for the auto system. when i took my 03 monte controls out it had vacuum position but electronic temp. not sure why they would use half and half for so long doesnt make sense to me.

Thanks Guys for chimming in. To answer a few more questions for you. Yes it is the full size truck with push button on the dash controls. I did the parking lot scrub test and no scrubing was noticed. I have in the past noticed this scrubing when forgetting to turn off the 4x4 and that was my reminder. I also tried 4x4 Low which only engages when in neutral. mine still works, you can hear a very definite clunk when turning it off and on as well as the tire scrubbing. So it sounds like my 4x4 High is not engaging. Whats next?

Thanks
E

put it up on stands,good solid ones on concrete or asphalt, check to see if the front wheels engage. you may have to drive it and put it in 4wd before you jack it up. but once up see if the front wheel turn and if the front driveshaft turns. there are two common failure items one is the hub actuator in the front diff, if the driveshaft is turning and the wheel arent or you can stop them the actuator might be bad, you can take it out and see it work back and forth if its good. the other is i think its called a encoder motor in the transfer case and the driveshaft wont turn.

Thanks jwfirebird. I'll do that. It sounds like those things will lead me in the right direction of the problem. From there it might be a trip to my mechanic.

Later
E