Hi guys, I am need of your expertise..I have a 98 blazer, with the 3 button 4wd. I have a problem with while in 2wd the front axle partially engaging while driving, I understand this is a vacuum issue of some sort. iI have replaced the front axle, (the diff in the old one went bad). the cable is free,

The 4wd engages, as it should, and holds as it should.

What I don't know is is this the 4wd actuator? Is it a vacuum line?? Is it a switch on the transfer case? If i knew how it worked I could diagnose better.

There are multiple threads on this issue, but I cannot find one that answered my questions, thank you for you shared knowledge.

 

The front actuator system is a weak design with lots of potential faults. I always bypass all the vacuum garbage and lock the front axle in full time. All this means is that the front driveshaft spins all the time, The bravada awd front axle is built locked in at all times, theres nothing wrong with doing it, adding the tiny amount of mass of the driveshaft for the drivetrain to get rotating is really nothing. Plus the vac line going to the transfer case from the engine side, so you wont have a vac leak. Pull the battery and battery tray so you can get to the actuator. I just squeeze down the actuator diaphragm and wrap a bunch of zip ties over it so it cant release. You need to put in 4x4 and jack up 1 front wheel so you can rotate it and make sure the front axle is fully engaged. Cheap ghetto fix. The only thing left in the system then is the shift motor on the transfer case locking in or out of 4x4. The weirdest thing i had happen was, shut vehicle off in 4x4, didnt know yet, but the seal between transmission and transfer case had failed and overfilled the t-case, the spring in the front actuator then pulled vac the other direction sucking in trans fluid, eventually trans fluid filled the vac reservoir and made its way the HVAC selector switch. WTF? Why is trans fluid dripping out of my dash??? Bypass that garbage and never worry about it again!
How its supposed to work....when you hit the button, the arm inside the transfer case thats moving the shift fork, also pushes on the mechanical vacuum switch, sending vacuum to the front axle actuator. The vacuum switch is a commonly replaced item, could be an internal leak in the switch allowing some vac to the front actuator? Ive seen all its issues and choose to basically delete it. Some people will cry gas mileage. You drive a 20 year old suv 🤣🤣 It seriously wont make a difference, except to the type of people that put a bottle of octane booster in thier prius and thier jaw hits the floor because of all the power they just gained...🤣🤣

 

Pull the cable line from the vacuum actuator that goes to the front diff. Put the truck in (N) then lock 4x4 (button) leave in neutral and set e brake. Take vise grips pull the line out about 5-10lbs pressure use pliers, and lock the vise grips onto the cable, around the squishy boot, going to your front diff. Tuck the vise grips in a safe space. Put truck in gear and test it. If so. Do what I did bypass all vacuum system and go with a pull/twist locker from Napa for 25$. My email is [email protected] if that’s your problem. I’ll email photos of the conversion. Took me about 1 hour to concert it. You can also search manual locker s10 blazer and should find the write up on it. Can’t remember the guy who did it. It’s genius work and easy to follow.