Vacuum issue and 4WD
 

Hey all, hoping someone can help. I have been doing a little research on the forum and think I have it pretty close to nailed down, but wanted to get some advice. My 2004 Blazer has an issue with vacuum. I had the intake manifold gasket replaced and when that was done, the tech said they fixed the vacuum line that they found broken. After leaving the facility, on the highway at speed, I started to get a "grinding" that can only be explained as like a toothed gear clicking on something. Stopped and it went away. Happened a few other times. Had it looked at again and a different facility said my vacuum lines were not put back correctly. No problem for a while.

Now, someone noticed a line that was not connected and sucking air. They plugged it and low and behold the noise came back. In my research, I found the line was supposed to be connected to the reservoir in the fender. When I plugged it in, noise is there. When I leave it open to suck air, no noise.....BUT, my HVAC is not venting properly.

I was told that the noise is the 4WD trying to engage and that it has to do with the vacuum actuator.

Can anyone help me in determining if this is the case? I have a push button 4WD, so I do not know if it even has one of these actuators or if it is all electronic. Also, how badly could the transmission or differentials been damaged from these occurances.

Any help is appreciated

Thanks
Carl

Carl - I've heard about this before on other forums, and somehow the vacuum lines are either installed incorrectly, or the transfer case vacuum switch is stuck open. Either way, you're getting vacuum to the actuator under the battery tray, when there's not supposed to be any vacuum. That grinding is your front hub locking, as it is when you're in 4WD, because the actuator is pulling on the cable that locks the hub. I don't think the grinding is going to damage anything short-term, but you won't want to run like that forever.

If the vacuum line to the resevoir wasn't connected (or plugged), you may not have been getting enough vacuum to the 4WD actuator under the batter tray for it to pull on the cable. Now that everything's connected and there's no open vacuum lines, the actuator is pulling on the cable again.

First thing I'd do is read through the link above and understand what all goes on in your vacuum system. Check and make sure all the vacuum lines are routed to where they're supposed to go, and are connected where they're supposed to be (both under the hood and at the transfer case vacuum swith connector plug thingy). Then, pull out the 4WD actuator and see if it's got any fluid in it. If you have an air compressor, disconnect the vacuum lines and blow air through there and see if any fluid comes out. Fluid is not something you want in there - means the t-case vacuum switch is bad. They are inexpensive and not too hard to replace, but that alone may not solve HVAC issues if you've got fluid in the lines.

If there's fluid in the lines, you'll need to dig into the dash, blow out the fluid from the small colored vacuum lines, and check the HVAC actuators. Problems in vent controls are almost always related to vacuum issues. A MityVac is just about a necessity if you want to tackle this yourself. It's the only foolproof way to confirm that you don't have leaks.

Also, check out Spittybays YouTube link:

https://blazerforum.com/forum/2nd-ge...problem-68831/

I think this is what happens when you let the grinding go on for awhile.....

Problem Solved???
 

So, per everyone's advice, I replaced the transfer case switch. Also, a friend of mine who was a GM mechanic, said the same thing. $20.00 and about and hour on the ground. I drove the truck, vacuum hose was plugged in and I was able to engage the 4WD. Drove about 25 miles at highway speeds today and no noise! I think that the switch was the culprit.

I will keep an eye and let everyone know. In the mean time I am going to change fluids and look for metal. Does anyone think that there would be damage to the transfer case, or would most of the issue be from where the grinding was in that half shaft and differential?

Thanks all,

Carl

Paranoia is not our friend. Don't worry, something else will go wrong before you have to worry about those.

Truer words have never been spoken

Addtional vacuum question
 

By chance, does anyone have a good photo of the vacuum lines that run under the hood and to the reservoir that is hidden in the fender? Just want to be sure I have everything right. Also, curious to know why it sounds like there is a ping pong ball bouncing around in my dash occasionally?

On a different note, with these Blazers, is it common to accelerate from a dead stop and shift first to 2nd, then feel an additional little "bump" (like another smaller shift) has occured? My truck seems to do it on occasion, more so when I really accelerate fast and just wanted to know what it could be if not normal.

Thank you

Check out this link; scroll down about 2/3s of the way. The only difference between this and yours is that plastic ball. Later versions, they made that reservoir more square-ish and moved it into the fender wall.

Also, this is for a 4WD. A 2WD would not have a tee that splits off to the transfer case.

On the transmission issue, that extra shift you're feeling may be the torque converter locking itself (or whatever the technical term is), but on my auto trans I usually only feel this when it's shifted into overdrive. But I believe the torque converter will do this in all gears.