Been doing bookoo homework on this vacuum issue I've been having and came across a frightening discovery - the transfer case switch can draw fluid into your vacuum system. Has anyone had any experience with this issue? What were your symptoms and how did you solve 'em? I know I'm grasping at straws here, but I gotta get this figured out. Driving me bats**t crazy here.

 

Root cause is most likely a bad seal between transmission and transfer case. Read more here.

 

The root cause is leaking O ring seals inside of the vacuum switch on the transfercase. When the seals leak, it applies vacuum to the inside the transfercase which pulls transmission fluid into the transfercase causing the fluid level to rise. When the fluid level reaches the vacuum switch, fluid is sucked into the lines. Symptoms are: 4WD is slow to engage or disengage, or totally inoperative. HVAC system inoperative or slow moving blend doors causing air flow to not blow where you select, or the inability to change air flow outlet. If/when this happens, the entire vacuum system must be cleaned completely....very time consuming, (several hours).

 

T-case is vented...no vacuum gets in there.

 

That is correct, provided the vent line and filter are not restricted.

 

so can you tell me the easiest way to get at the vacuum switch? book says to take out the center console...

 

Vacuum switch is located on top of the transfer case. Follow the front drive shaft back to the transfer case and look for 3 rubber vacuum lines converging on top of the t-case. The lines are connected to the switch. Switch can be removed with a 7/8" wrench. It's a little tight up in there...be patient.

 

I just fixed mine last weekend. First pull the fill plug out of the transfer case and see how much extra fluid is in the transfer case. If there is any, you need to replace the seal before you do anything else. The seal is $11, dont buy the cheap one. You can replace the seal without dropping the case. (My Blazer is a 01 ZR2). Remove the shafts, take out the tranny mount and cross member. Drop the tranny down until the trasnfer case is resting on the torsion bar cross member (as low as it will go). Remove the encoder harness and the other plug. Remove the bolts that hold the transfer case to the the tranny. Leave the adaptor plate on the transmission. The case is around 60 pounds. It probably will not come out but don't get your head smashed. Push the case back as far as you can get it and twist the front toward the passenger side. You will see the seal. the seal retainer is held on by 4 bolts. They have sealant on them so be prepared to fight them the whole way out. The retainer is sealed to the case but there is a hole/slot in the side to get a small prybar in there. I'd say its at like 10 o'clock. Pop it off rejoice. It will clear the transmission if you buggy lug the case around. Replace the seal and put it back together. My tranny friend, well wait let me rephrase that, my friend that works in a transmission shop tells me the best sealant to use is Ultra Gray. There is no paper gasket available to replace the one between the transfer case and the adaptor. Use the Ultra Gray there too. Just get up in there and make sure both surfaces are clean and remember its aluminum so don't get all nuts up there with a razor. Put it back together easy squeezy.

Now you got the leak fixed, replace the vacuum switch. While the plug is off spray compressed air down from the feed line over by the brake booster. Clean it with simple greem or something or replace the line. Then take your dash off and your AC panel off. The blend door dealio had a vacuum switch that needs to come off and be cleaned. On mine, the switch itself had gone bad from the fluid. I had to replace, I could not get it to stop hissing. New one fixed it. You may or may not have lost one of the blend door actuators. Check em and replace. If they are good try and clean em. Tranny fluid will kill em over time. Next take the battery out and check the 4x4 actuator under the tray. Mive still worked but I can feel its slimey inside like there is some fluid in there. Its not going to last much longer, but its easy to swap. If yours is holding vacuum its your call whether or not to change it.

 

AintQik, I aint e-ther. Are you loosening the tranny from the motor in any of this?

 

No, no need to remove the transmission from the motor or even loosen it up.

Lol, my screen name comes from my street racing days down south. People would ask me if my car was fast and I would say, "naw it aint quick". Kinda stuck. Most of my cars are forced induction and kinda quick lol.

Also, the OP never said if he had fluid in the lines or was just searching around trying to figure out how it might happen. Don't do all that stuff if you don't have fluid lol.

I have heard a bunch that even if the vacuum switch is bad it won't really pull fluid if the fluid is at the correct level. My experience has been that all of them that pulled fluid needed seals. Can't say that it doesn't happen, but I've not seen it. The presence of fluid usually indicates 2 problems, the switch is bad AND the case is overserviced. Case will only be overserviced if Bubba put too much in, or the seal has gone bad. My was like a piece of toast. Just crumbled when I touched it. I was 3 qts over. Yes, the tranny was down. If you want to do a quick check, check the tranny level.