Take the battery out and squeez the diapragm and then plug the hose that goes to it. If it stays wrinkle then it is good. To test the cable for being stuck jack the front with both tires in the air and take off the cable going to this diagram and pull it with pliers as you slowly turn one tire bac and forth. You should hear it click into place and now the tire will be harder to turn since you are turning the other one too. As soon as you let it go and turn the tire slowly bac and forth it should let go and you will feel it. The cable only has to move milimeters ok??? And yes the corrosion can be an issue too so you may want to clean that up. remeber to witch between 2wd and 4wd the car should be in neutral and you cannot just switch from 4wd low to 4wd high, you should go to 2wd before.

 

I am also having a shifting problem. When I bought my Blazer the 4 wheel drive did not work. There was a bad spot on the cable so I replaced the shift cable. I noticed at that point that the vacuum line was plugged with a bolt going to the actuator. I thought nothing of it and just hooked the vacuum line back up. Everything worked fine for a couple of weeks.

Then one day it seemed as if the front axles had locked in on their own without me pushing any buttons. I pulled over and shifted it in and out of 4 wheel drive a few times and pulled off with no more problems. This happened a couple more times over a period of about a month. I took a trip of about 150 miles and as I was going downhill from a huge bridge the front wheels suddenly locked again. I shifted in and out of 4 wheel drive several times before I could get it to release. I went to a couple of mechanics shops and no one wanted to look at it. I then started thinking about each time that this problem had come up that I was always going down hill. I pulled the hose off the actuator and plugged it off again. I made the entire trip back home without problems.

Now my theory is that since I was going down a steep hill each time this happened there must be a link. The car is pushing the engine at this point and the vacuum must be at it's all time high. I am thinking that at this point that the high vacuum could be causing an old vacuum switch to leak through thus causing the actuator to get vacuum and pull the cable at the wrong time.

Anyone have an idea on this? I really miss the 4 wheel drive since I have been spoiled using it.

 

Yeah that's strange, well try putting in a new vacuum solenoid from either the junk yard or a new one.

 

use a pull cable setup to engage your front differential, you wont have to worry about the actuator and any vacuum at all. this setup bypasses all that junk..... MAKE IT SIMPLE

 

hey i read ove rthe posi lock page. whats the purpose of putting the bolt in the vacuum line? and the cable on the actuator, where does it go. srry im new to the whole 4x4 trouble shootin thing and im seriously considering the posilock thing. someone please explain how the vacuum system works. o and fyi i think the vacuum hoses behind my engine that connect to the solenoid are both badly corroded to the point of crumbling in my hands, if thats any help

 

It's actually called an VACUUM ACTUATOR. Not a solenoid. A solenoid is an electrical part.

 

plugging the vacuum line is to keep out the dirt i guess... it didnt effect the way the 4x4 worked when i didnt have it plugged. also, the cable going to the actuator is coming from the front differential, if you give it a yank, itll lock your fron diff. into 4x4.personally i like the cable locking system, it hasnt failed me yet. IF you do decide to go this route, remember to always disengage the front diff. when you go back into 2 wd.

 

ok so i read up on the 4x4 system and actually tinkered on my truck. i get it now. im going tomorrow to get the cable cuz i tried the trick where u jack up the front and pull the cable. i was so excited, i felt like a little kid. so im definately gonna use the cable system. thanks alot.