Vacuum Check Valve Problem
 

Hi all,
I have came across an issue with the Vacuum Check Valve my 2002 Blazer 4.3l L35 w/ 3 button 4WD 233 case.
Well I had the traditional no floor or only face vent air working in the HVAC system. So I pulled the actuator that is right behind the glove box because it was leaking. I cut it open to find water/oil mix inside it. So i figured my Transfer Case Vacuum Switch and or trans. seal was bad and sucking trans fuild into the system. But I was not confident it was trans fuild. The front diff actuator was dry as a bone. I went on and pulled the other actuators on the drivers side for defrost and mode. They were too filled with the same watery oil mix fuild and rusting out the metel inside the actuators. I than studied the vacuum diagram very hard to see what else it could be. I have concluded that the Vacuum Check Valve was cloged with the same watery oil mix. Basicaly when the engine is shut off the actuators want to relax and pull air from the intake plenum and since the check valve was cloged or bad it allowed this to happen. Basicaly the PCV tube goes right into the same port the vacuum line is and this is where the water oil mix is coming from. Condesation is always up there and mixes with the oil since this vehicle only sees 2 miles to and from work a day. I have tested the check valve out of the system and I can get air to pass though it at very low pressure. The new one is a different PN than the old one and works the way a check valve should work. It sucks that a $2.00 part killed $120 dallors of actuators. But thats the way it always is I guess.
I just wanted to post this to see if any else came across this and help others
Thanks

If you haven't pulled the fill plug on the transfer case, I'd do that now. I have never seen a system pull in moisture through the engine before and I have been messing with vehicles of various makes/models having vacuum controlled components for over 20 years.

The point you made about the front axle actuator would only make sense if you were driving around in 4wd all the time which I doubt is the case. If the majority of your time is spent in 2HI, then the actuator would not be connected to the vac system, just vented to the atmosphere.

I say all of this because it would suck for you to replace a $2 part along with $120 in actuators only to have the problem again.

If you haven't pulled the fill plug on the transfer case, I'd do that now. I have never seen a system pull in moisture through the engine before and I have been messing with vehicles of various makes/models having vacuum controlled components for over 20 years with one exception, a car that was a flood victim...

The point you made about the front axle actuator would only make sense if you were driving around in 4wd all the time which I doubt is the case. If the majority of your time is spent in 2HI, then the actuator would not be connected to the vac system, just vented to the atmosphere.

I say all of this because it would suck for you to replace a $2 part along with $120 in actuators only to have the problem again.

That is kinda strange...I never got much fluid in the dash actuators, even in my Sonoma which went a long time (I am assuming) with a bad vacuum switch (see this thread...the t-case was very over-full). The Sonoma did have a lot of tranny fluid in the front diff actuator, and both of my trucks had a lot accumlate in the vacuum reservoirs.

Let us know what you find in the t-case.

I haven't pulled the fill plug yet but I am planing on it, I also have a new Transfer case vacuum switch also, just didn't want to install it untill I checked the trans seal.
The reason why I did not look harder into the vaccum switch and seal was because the check valve was not working correctly and only one side of my actuators where filled with the brown water oil mixture. Thats why I thought it was moisture coming in when the actuators relaxed. And the truck basicaly doesn't run long enough to burn off the moisture/ condesation within the valve covers, pcv tube etc. The vacuum hose from the plenum to the check valve had the same water oil mixture in it.
I do have a question about the vacuum switch, basicaly when in 2WD the actuator is open to vent and vac is sealed and when in 4WD the actuator is open to vac and vent is sealed, correct?
The truck is 95% of the time in 2WD. So wouldn't my front diff actuator fill with fuild from the vent lines if the trans seal was bad?
And would transfer case fuild rust the metal parts inside the actuators? These simple switches can really play with your brain sometimes.
Thanks

When vented, there isn't anything drawing fluid into the lines. Vacuum is the reason for fluid getting into the lines.

As far as the rust, transmission fluid should protect metal, but I still find it VERY hard to believe that moisture from the engine was the primary cause of your problem.

So since my front actuator being dry wouldn't that give me an idea that the transfer case vaccuum switch and trans seal may be fine?

Not in my opinion. In the time you have spent thinking about it, you could have pulled the fill plug on the transfer case...

I agree, I will check the fill plug after work to be safe.
Thanks

Well I checked the fill plug after work today and the level was fine. So I went ahead and put the truck in 4WD HI and let it run for alittle while I was keeping an eye on the vacuum check valve I noticed the fluid being sucked into the main vac line. The new check valve is made of a clearer plastic than the old one and you are able to see inside it with a flashlite behind it. Well that was sure enough to say pull the transfer case vacuum switch. Is was bad checked it with my own mouth pressure. I cleaned the vac lines with alcohol. ,put the new vacuum switch in and put everything back together. Just to be sure there was nothing else bringing fluid into the system I ran the truck again for awhile and watched the check valve. There was no more fluid visible.
I want to thank swartllk for really making check the seal which made me check the vacuum switch also.
Thank god the seal wasn't bad as I didn't want to get into that. I guess the reason why I felt is was only the check valve was because that was clogged and the fluid in the actuators was brown and rusty.
Thanks again