First off, now that I'm not crammed under a SUV and have a second, thanks a ton for your help so far Captain. I understand how old it gets when someone posts a thread on a subject that has been covered countless times. I truly attempted to use the past threads on the subject before posting a new thread.. Anyways.

I attempted to removed the fill plug to see if any excess fluid spilled out, with no luck. My car is not on jacks, and it was very difficult to get leverage, and it would not budge. It *slightly* felt like it started to strip, but I don't believe it did. At this point I stopped.

From the actuator I can see two "lines", the actuator cable, and a vacuum line that runs straight down, along side the motor, and towards the fire wall. This was my third time checking that vacuum line and sure enough I was able to find a tear! Near the back of the motor, where the plastic cover ends, there was a half inch tear. I kept following the hose to see where it went, and it seems to join another hose at an intersection near the firewall, behind an unknown part, which is obstructing my view. [See Photo]. Is there actually a junction here or is it just multiple hoses running net to each other?

So, I've found two problems so far.. the vacuum actuator switch was broken (the ball was stuck pressed in), and I found a torn vacuum hose.

 

This shows the vacuum line routing. It is not exactly how it is on the vehicle for illustration purposes.

The vent line connection on top of the transfer case, is just above the vacuum switch. There is a Tee quite close to the connection. One side goes to the filter on the trans dipstick tube, the other side goes to the vacuum switch.

 

Awesome, that helps clear things up. Do you know what size the vacuum hoses are? I'd prefer to have the new hose with me while I pull out the old hose so I can reference where it runs. Oreilly's website says there isn't one available for the specifiic model, but I'm guessing thats because the hoses are generic.

 

Did my vacuum hoses a week or so ago on my '98. I believe they were 5/32. Don't know if they are the same for your truck. But if they are still the factory hoses, if you look real close, you can probably make out the GM part# and the hose size. It's printed continuously on the hose in faded white.

If you go to any auto parts store, they probably have spools in the back they will take you to. Walk up and tell them you need 25 feet of 5/32 vacuum line. Double check for your sizes and length needed though. Those specs were for my '98.

 

I was following this thread to fix my 96 Blazers problem shifting into 4HI-- I was checking my actuator vacuum line for cracks/leaks and when I pulled the line off the tee---tranny fluid leaks like crazy from hose and tee!!!!so I have to clean all the vacuum lines and the actuator and replace the vacuum switch-- What exactly has happened here? the vacuum switch is doing what? How is it getting fluid? How does it make the transfer case level high? Is the fluid getting into HVAC/heater vacuum lines too? the intake too? Yikes! Anything else I should know?Sure glad for this post --- thanks guys

 

I re-used an oil-filled actuator on my '96 Sonoma. Think I just let the fluid drip out and maybe hooked up a MityVac to the diaphragm for awhile, to suck out the residual. It tested ok for holding vacuum, so I didn't replace it. Other actuators (HVAC), I replaced because the fluid caused the diaphragms to not hold vacuum anymore.

 

So many questions, so little time

I believe rockp2 is correct for the vacuum line diameter, 5/32" sounds right. As for length, better to have too much than not enough, 25' should cover it.

Kenlani, The vacuum switch on the transfer case has a plastic housing and a brass spool valve inside with O rings to seal the vacuum when the spool valve slides. If/when the O rings leak vacuum, it applies a negative pressure, (vacuum) inside the transfer case. There is a small black plastic filter attached near the top of the transmission dipstick tube: If the filter is restricted, it will allow vacuum to increase inside the transfer case. Transmission fluid is sucked from the transmission into the transfer case, which causes the fluid level in the transfer case to rise, and the transmission fluid level to decrease. When the fluid level reaches the vacuum switch, the fluid passes the O rings in the vacuum switch and is sucked into the vacuum system for the 4WD and the HVAC. Once the fluid is in the lines, the vacuum systems have now become hydraulic systems. The vacuum actuators, both 4WD and HVAC, will operate slowly, and eventually stop working. Transmission fluid will soften, distort, and eventually destroy certain types of rubber, including vacuum lines for 4WD & HVAC, (in the dash & under the hood) O rings, HVAC mode switch, 4WD axle actuator, HVAC actuators under the dash, etc etc.*** The entire system must be flushed and new lines, actuators, switches, etc replaced if/as necessary. The root cause is the vacuum switch on the transfer case, replace it! The transfer case input shaft seal may need replacement as well.


***Same thing applies if transmission fluid is added to the brake, (master cylinder) hydraulic system. All rubber parts must be replaced. Master cyl, flex hoses, calipers, wheel cylinders, etc.

aa21830, If your 4WD axle actuator diaphragm was exposed to transmission fluid, it will eventually end up like your HVAC actuators.

 

Thank You Captain for the quick reply---Oh Boy--looks like I've got work to do before the snow------Again thanks for the reply--but I'm still puzzled as to how the transfer case sucks fluid from the transmission-and I guess I should replace the filter on the dipstick

 

The vacuum in the transfer case sucks the fluid out of the transmission and into the transfer case past the input shaft seal, most of the time without an external leak.** At least check the filter, you should be able to blow and suck through it quite easily. If there is fluid in the line to the filter, it will restrict the flow through the filter and allow vacuum to build inside the transfer case.

** In post #12 you can see the seal on the adapter where it bolts to the transmission. There is a gasket between the adapter and the transfer case and a seal on the input shaft, that's where the fluid passes through into the transfer case.

 

I have a differing view on the root cause, and it is one that will continue to plague anyone who gets fluid in their vacuum lines until it is fixed: a leaky t-case input seal. Until that is fixed, your t-case will continue to overfill. Once it gets full enough, fluid will push on the vacuum switch seals. Eventually, the seals will give - either because of age, or inability to withstand the pressure of hot, expanding transmission fluid.

It is unlikely that a bad seal on the vacuum switch, on its own, will suck fluid into the lines, for a couple of reasons. First, the t-case is vented. Unless the vent line is severely clogged, there won't be any negative pressure in the t-case. Perhaps the vent line could contact something hot and get melted completely shut. It's possible...maybe.

Even if that happens, the transfer case (with a good input seal) is not meant to be completely full of fluid. There's approx. 2 quarts of excess air space in there. Since the vacuum switch sits on top of the t-case, it shouldn't be in contact with any fluid, except maybe some that gets sloshed around. So you can apply all the negative pressure the vaccum system can provide, but if the t-case has the proper fluid level, the fluid won't rise from the bottom of the t-case to the top and get sucked into the lines. Don't think physics laws would allow it.

Don't mean to argue....I just don't want people to have to go through this exercise multiple times (like me) because they didn't fix the input seal.