As I was checking my vacuum hose to the 4WD actuator at the firewall I discovered tranny fluid in the vacuum hoses which means I have a faulty vacuum switch at the transfer case.....I will clean out the hoses and the actuator, and replace the vacuum switch. I dont know what is happening here though-- -- where is the switch getting the tranny fluid from? -- I haven't checked the transfer case level but have read that it may now be overfilled--why is that? -- why wouldn't the fluid have all been sucked into the engine? -- do I need to check other (HVAC/heater)actuators?Is there anything else I should think about?

 

These links will tell you what's going on and how to fix. Read them in order:

GMC Sonoma & Chevy S-10 Transfer Case Vacuum Switch

GMC Sonoma & Chevy S-10 Transfer Case Vacuum Switch

 

most transfercases take trans fluid so its just sucking fluid into the switch. it may slowly be getting sucked into the engine but the engine is probably just burning it

 

Okey Dokey---I replaced the switch (what a PITA-remove skid plate , get short wrench, awkward position with short strokes to get out- then replaced) I then blew out the vacuum lines and the vent lineNow I want to clean out the fluid from the vacuum lines to the heater/ac system under the dash--any ideas folks?

 

That first link I sent you has a link at the end of the page that goes into the dash work.

 

Thanks for the great advice --I really appreciate your help-----I think I will wait to do the dash work(holy moly!) But I'm Wondering why the engine wouldn't just suck the fluid in so I dont have to clean the lines

 

Well I've done a lot of reading on this vac switch and 4wd...
Anyways: what got me started was the random vibration / whinning when driving in 2wd; if I put it in 4wd the sound would immediately go away.
So tonight I changed the vacum switch on the T.case and changed the t.case fluid while I was down there to find out that it was over full... figures.. input seal. Also changed front diff fluid.
On the Old vac switch: the ball seemed to be stuck IN, the new one the ball was out further and moves in and out.
I start it up and now have NO 4wd. Light on 4wd button is lit up.
So I put the old vac switch in for now, and my 4wd is back.

Obviously I need to get the input seal changed, but my question is... why didn't the 4wd work with the NEW vac switch ??? The hoses only fit on one way with the "little key" that is between the two hoses.

 

I had the same issue and have been chasing drivability and front end "noises" since. Like the truck, but what a pain in the ***!

 

I just realized I havent updated this thread -- I replaced switch , blew out lines and had input shaft seal replaced (Transfer case was way over full) also had bad u-joint -- did'nt blow out all the vacuum lines, just capped/plugged the vacuum lines to HVAC and run the heater on default which is defrost/floor and it works well for wintertime so I'm good....Sevillian, Well I don't understand either why the old switch works and the new don't -- I can only suggest one thing-- I have read that there is a small percentage of after market switches that dont work.....I assume you blew out the actuator vacuum line, so now the old switch, line and actuator are operating properly but will probably fail to work properly again as soon as the transfer case fills up due to the input seal.

 

How tightly did the new vacuum switch "prongs" fit into the rubber junction thing? The Doorman aftermarket switch I put in my '04 Blazer fit too loosely, and there wasn't a good vacuum seal. It would not engage the vacuum actuator under the battery tray (even though dash lights lit up as if it were in 4WD). I wrapped duct tape around the prongs to create a tighter seal, which worked.