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Discussion Starter #1
My 4wd hasn't worked in years. I've decided I want to get it working again before winter. It seems to be a vacuum issue.

I can put a mighty-vac on tee fitting near the vacuum actuator and it pulls in all the way at about 15" of vacuum. I thought it must be the switch on the transfer case then so I replaced that today but it still doesn't work. If I pull the little connector off the transfer case switch and apply vacuum to the line going to the actuator, I get nothing. In fact, none of the lines seem to pull a vacuum. A visual inspection showed nothing obviously wrong with the line to the actuator as far as I can see so the problem must be somewhere I can't see. Any tips on pulling a new 5/32 vacuum line through that conduit that snakes through the engine compartment? Is it easier to start at the top or the bottom?
 

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B4U Task Force Admin
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Whoa...slow down there cowboy. If your truck is a 98+, there is a vacuum can in the drivers fender hidden behind the abs unit. Take a look and see if the nipple is broken. If not, carefully remove the line....otherwise you will have a broken nipple. A couple of choices...remove the fender and replace it with one from a j/y, or find a spot foe the old style round one.
 

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Discussion Starter #3
It's a 96. The vacuum can is on the underside of the hood and is new as are the vacuum lines going to it and all the way back to the engine. I replaced the vacuum ball because as you mentioned, the nipple was broken off. Replacing that and the line going to the engine did at least fix my HVAC issues and took care of an off idle stumble I had.
 

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I guess I should have guessed you had a 96...lol

You did use the one way valve...right?
 

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Discussion Starter #5
Yes. It is still there. Original. What really fixed the off idle stumble and HVAC vent issues was replacing the hose going from the intake "tee" to the one way valve. It was crumbly and had a slit in it and was crushed under the air intake.
Didn't help my 4wd though...
 

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You could have stuck transfer case vacuum valve. Only 2 of the lines are vacuum. One is from the engine and the other is to the 4wd actuator. The third is a vent line.
Here's a sticky that explains a lot about the 4wd vacuum:
 

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Discussion Starter #7
True, but if I remove that 3 hose connector from the transfer case switch and apply vacuum to the appropriate port/hose, I should see the actuator pull in, right? It doesn't. I thought perhaps the hoses weren't in the right spots so I tried all of them and none of them cause the actuator to operate. I know the actuator works because I can apply vacuum to the tee behind the battery and it pulls in. On my truck there is a tee fitting where one line (about 12") goes to the actuator and another, larger hose (maybe 8" long) goes to some kind of vacuum operated switch mounted to the passenger side fender right next to the negative battery terminal. I think it has something to do with the ABS determining when 4wd is active. I can pull a vacuum at the input to the tee fitting and the actuator operates so it's nothing to do with that switch.

This is why I'm thinking the vacuum hose running through the conduit and disappearing behind the engine has a problem.

Not that there couldn't be other issues, but I don't think the problem is on the drivers side.
 

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Try running a hose from the TC switch to the actuator. If it works leave it in place of the one you can't follow. It likely has a leak.
Be sure the replacement hose is not near any exhaust parts.
From the link above:
343338
 

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Discussion Starter #9
Well, I tried pulling a new hose through the conduit but couldn't reach the zip tie in back of the engine to release the old one so I ended up fishing a new one along side. Now I have vacuum all the way to the actuator when in 4Hi. I'm not sure the 4wd is working yet though because even though I can hear something make a faint "clink" sound in the front when I press the button, It doesn't "feel" like it's engaging. Next step will be to rig up some jumper cables so I can start the truck with the battery out and see if the actuator is pulling in enough. It's possible the cable is too stiff from at least 10 years of non-use.
 

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My 4wd wouldn't work in my 03, ended up being a rotten vacuum line. So i ran a new line from the transfer case switch to the 4wd actuator under the battery, except I ran it further away from the engine as the heat from the engine caused the stock one to deteriorate there.

I had thought maybe it was a bad actuator so i replaced that first with a Dorman made one. The Dorman was cheap garbage. Stiff, sticky, wouldnt work with the new vac line. I ended up putting the old actuator back in and my problems were fixed.
 
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