I don't know if this has been addressed before. I am sure at some point is has. My 4WD system is not working. 97 model 4.3L. The switch is working. I can put it in 4HI or 4LO and I can hear the transfer case engage. The front diff will not lock. I ran all new vacuum lines (including the one to the actuator) and it still will not lock. I even went as far as to close the actuator to where it should engage the front diff and secured it and it still will not lock. Any ideas??? We just had a TON of rain and i want to go play!!!!!!!

 

When you push the 4x4 button to engage it, does the actuator under the battery tray suck down and pull the cable to the diff? If it does, then with the 4x4 engaged reach under the truck and see if you can turn the front drive shaft. If it cannot turn, and the actuator is pulling properly then the problem is in the front diff itself.

 

Yup, this ones been asked a lot. Check this:

https://blazerforum.com/forum/tech-a...ill-help-7180/

 

ok. so i checked out my driveshaft from the t-case to the front diff and it is locked while in 4WD. the cable for the actuator to lock the front diff is engaged but it still will not lock. any ideas where to go from here? i had to go play in 2WD and it is not as much fun lol

 

Is the driveshaft locked by the transfer case, or front differential?

If the actuator is fully engaged and the T/C is in locked in 4wd, the next thing would be broken differential parts or a broken CV shaft.

 

thats what i was starting to think... something internal in the front diff... when i have some down time i will have to rip the cover off and see what is going on.

 

reading this brought this video to mind

 

quick update.. after replacing basically all the vacuum lines (which now my a/c blows again lol) the transfer case is locking the driveshaft to the front diff when it is in switched into 4wd. The actuator is manually closed but when it is in 2wd the driveshaft will spin freely.. is this normal operation? I have the actuator pulled all the way closed and have it zip tied in the closed position. could this be pulling the cable too far and causing the diff to not lock?