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3 Leaf Fab
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a lot of people have problems with their 4x4 not working, for various reasons. one of the common reasons is the vacuum actuator going bad, or the vacuum lines going to it. i have gotten a PM from somebody, and i figured i could share some of the info with everyone.

in s10's, when you put it in 4wd (4hi or 4low) with either the 233 (push button) or 231 (manual shift(also 207)), the transfer case has a switch of sorts that tells the front axle to engage. this switch routes vacuum to one of two places. if you are in 4wd (hi or low), the vacuum goes to the actuator. if you are in 2hi then the vacuum gets routed to an orb where it is just stored. this line also supplies the vacuum.

now, the switch it self is on the drivers side, almost at the front of the t-case. it has three vacuum lines going to it. the switch works similar to a ball point pen, meaning there is a round ball that is either pushed or not. the ball gets pushed by the shift fork inside the t-case, when the case is shifted into 4wd. now, there are three vacuum lines going to the switch. one line supplies the vacuum, and stores it in the orb when not in 4wd. one line vents to the open air, and the t-case vent piggy backs onto it. the other line goes to the actuator. all three lines run together up to the passenger side of the bell housing. then two go one way, and one goes the other. the vacuum supply/orb is the line that breaks from the pack and follows over to the drivers side. the other two lines, the vent and the actuator line, continue to run along the passenger side frame rail where they end near the vacuum actuator. one line plugs into the actuator and the other is just a vent that clips onto the inside of the outer fender well.

the actuator takes the vacuum, when supplied, and has a diaphragm that pulls on a cable. this cable runs down to the passenger side of the front differential, and moves a collar back and forth. this collar either connects the passenger side cv shaft to the carrier, or it disconnects it. this is how the 4wd system works on an s10, and all IFS 4x4 gm products (with a few variants).

now the pictures:

this is the switch installed on a 231. note the vent line coming off the t-case


here is where the t-case vent line meets up with the open air circuit.


you can see the lines running along the trans and bell housing


this line goes off to the orb, and supplies the vacuum from the engine


this line will follow the wiring harness and go the orb, located behind the drivers side headlight


this is the orb, aka the vacuum canister


this is where the switch gets vacuum, off the intake


this is the other two lines that go off to the passenger side


they end behind the passenger side headlight


this is the line going into the actuator


the actuator is under the battery tray




now onto the switch. the switch looks like this


if you look at the top, where the lines go in you will notice a little "key"


this lines up with a similar spot on the female end


the three vacuum lines must be in the right spot in order to function properly. take the female end of the vacuum lines, looking at the open end towards you like in the above pic. if you orientate it to where the key is on top, the lines are as follows


if anyone has any questions, or wants any more pics, just ask.
 

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100% A-hole
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246 Posts
Very good write up Don...

The only downfall tho...those vaccum lines and switches on the side of the tcase are not easiest to get to with the body on...It can become a major pain....But you hit the nail on the head...
 

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I Rather Be Wheelin'
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4,864 Posts
The vacuum actuator on my truck isn't under the battery tray, it's on the wheel well and extremely accessible (which is nice if it ever dies, but thank god it works perfectly still). My '91 parts truck had it under the battery tray before I removed it.


Three years ago before I was into the S10/S15 scene I had a loaner Blazer... I found out the hard way that the 4WD didn't work (vaccuum actuator):




Had to get pulled out by the blue 2WD dodge behind that hideous camper thing, it was quite embarrassing :haha:
 

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Registered Asshole
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4,125 Posts
^^That chick is prolly thinkin... "Man, whatta loser"

but yeah... def a good write up donahue! i cringe when i have to explain this whole process to folks... so it's def nice that you were able to get pics of the whole system now that you have your body off! now i can just link to this thread when i get this question! thanks donahue!
 

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3 Leaf Fab
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4,082 Posts
Discussion Starter #6
when you go sfa, just unplug the lines at the t-case, leaving the switch in there so the t-case doesnt leak atf everywhere. you will want to cap the line coming off the engine so you dont have a vacuum leak. then just remove everything else as it is not needed anymore. that is unless you wanted to hook up the vac disconnect system on a waggy axle or something.
 

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Registered
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343 Posts
Can the mods add this to the sticky at the top of the page?
 

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American Muslce
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227 Posts
Is there any chance you could show me where your other vac lines go from the TBI? I have an 86 and the diagram I have is not showing me the stuff for the 4x4 and I think one of my lines is messed up or missing.
 

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3 Leaf Fab
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4,082 Posts
Discussion Starter #9
Is there any chance you could show me where your other vac lines go from the TBI? I have an 86 and the diagram I have is not showing me the stuff for the 4x4 and I think one of my lines is messed up or missing.
yeah, do you just want a more specific pic of the vac line coming off the intake? you are talking about the one that supplies vac to the t-case right?
 

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American Muslce
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227 Posts
yeah, do you just want a more specific pic of the vac line coming off the intake? you are talking about the one that supplies vac to the t-case right?
Yeah I need a better one of the one coming off the Intake and tbi. I'm tring to figure out if all of mine are hooked up to the TBi and intake like they should. My truck for some reason has no power brakes and its running rough so I am thinking that a vac line isnt hooked wp right.
 

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American Muslce
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227 Posts
Also where is your ORB located? I cant seem to find it on my truck.
 

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Registered
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very good write up. Definatly needs to become a sticky.
I have a question:
The three vac lines @ the transfer case. Do they have to be plugged in a certain way from the Tcase? After I put a trans in my truck, I plugged it back in as best as I could remember, and the 4wd worked. I used it like once. Then it stopped working altogether. Even low did nothing. So I got under there and that three line fitting came unplugged. I plugged it back in (wasn't sure if it needed to be plugged in a certain way), and now my front drive shaft spins, and it goes into low, but still no 4wd.
I know it sounds like the vac act. but if that line is plugged in wrong will the actuator not get what it needs to do what it does? How can I tell how it needs to be pluged in without dropping my Tcase? Trail and error??
 

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3 Leaf Fab
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4,082 Posts
Discussion Starter #15 (Edited)
very good write up. Definatly needs to become a sticky.
I have a question:
The three vac lines @ the transfer case. Do they have to be plugged in a certain way from the Tcase? After I put a trans in my truck, I plugged it back in as best as I could remember, and the 4wd worked. I used it like once. Then it stopped working altogether. Even low did nothing. So I got under there and that three line fitting came unplugged. I plugged it back in (wasn't sure if it needed to be plugged in a certain way), and now my front drive shaft spins, and it goes into low, but still no 4wd.
I know it sounds like the vac act. but if that line is plugged in wrong will the actuator not get what it needs to do what it does? How can I tell how it needs to be pluged in without dropping my Tcase? Trail and error??
correct, if they are plugged in wrong at the t-case it might not lock up. plug them in according to this:





make sure you line up the little "key". it only goes on one way.
 

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American Muslce
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227 Posts
Yeah my truck doesnt have a ORB on it. The air line just stops and has a plug on it. I can take a picture of it if you want.
 

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3 Leaf Fab
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4,082 Posts
Discussion Starter #17
Yeah my truck doesnt have a ORB on it. The air line just stops and has a plug on it. I can take a picture of it if you want.
apparently there are a few irregularities. but you get the general idea. i didnt even know what that orb thing was or that i had one until i threw it away.
 

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I Rather Be Wheelin'
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4,864 Posts
^^That chick is prolly thinkin... "Man, whatta loser"
That's my cousin, she was in the truck with me when the POS got stuck :haha:
 

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4x4 v6 blazer
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7,521 Posts
apparently there are a few irregularities. but you get the general idea. i didnt even know what that orb thing was or that i had one until i threw it away.

Vacuum canister
 
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