vacuum, transfer case axle or 4x4 problem

Discussion in 'Chevy S10 Forum (GMC Sonoma)' started by spac16, Feb 9, 2013.

  1. spac16

    spac16 New Member

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    New member here guys have been reading topics on here for years. As I know just enough to be danderous I never posted a answer cause I wouldn,t trust myself.
    So heres the problem 99 Sonoma highrider 4.3 liter. Put the truck in 4wd a couple months ago to go for a ride on beach. Truck seemed to go in and out smoothly. On way home from beach pulled over for what sounded & felt like a flat while slowing down noticed it was underneath truck. possible transfer case or axle felt like it was trying to engage. Got home found a couple small holes in vacuum line replaced all of them. Problem still there. Replaced vacuum switch on transfer case no oil in lines problem still there. noticed if I undo vac hose to the vac resivor no more grinding sound from axle transfer case area. Push button 4wd shifter on dash shifts no problems can here motor shifting it and no trouble lights.
    Anyway I have read alot of the the other topics on here about vac issues and could not find that directly dealt with this. Any advice would be appreciated. Thanks
    Also with vacuum resivor unpluged I loss my defroster and floor heat and really need to get this fixed as that is the way I am currently driving this.[/TD]
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    Last edited by a moderator: Apr 16, 2013
  2. xpackdeals

    xpackdeals New Member

    We replaced vac switch with advanced auto switch didnt work wouldnt draw vac for acuator bought gm switch works great also on a 1998 there is a breather for the transfer case vac switch that is attached to transmission fill tube (dipstick) you might see if its plugged hope this helps
  3. AndyLett

    AndyLett New Member

    New member here. I'm working on a 98 Sonoma 4X transfer case switch. There is oil from the transfer case in the vent hose. On my 98 Sierra 4X the seal between the auto trans and the transfer case leaked so the tranny forced oil into the transfer case which subsequently came out the vent tube and leaked onto the exhaust manifold =lots of smoke!! I'm wondering if its worth changing the transfer case switch IF the Sonoma has the same problem. The hoses to/from the switch are hard to follow as they disappear over the top of the trans. Is the vent tube just tied to the dipstick? It's hard to see back behind the motor.
  4. thegawd

    thegawd Rockstar 2 Years 1000 Posts

    ya that hose is just a vent and yes it does run up to the dipstick and is bolted to the housing there it does not connect to anything and ends there. I almost plugged the darn thing during a tranny swap on my burb... thats why I know lol. its just atf in the tranny case, and shouldnt come out of the vent unless the vent is unbolted and falls below the tcase. did you park or drive down a crazy hill? im only a back yard mech but I cant think of any other reason why the fluid would come out of the vent. the vent hose has nothing to do with switching from 2wd to 4wd just helps regulate pressure with temp changes during operation...

    sorry im not really awnsering your question but that is what I know.

    take care
    Last edited: Dec 29, 2014
  5. AndyLett

    AndyLett New Member

    Yeah Al your answer did help. I've gotta replace all the vacuum switch hoses but couldn't figure out why the vent hose wouldn't pull down under the truck! I guess I'll just run a new vent hose and ziptie it somewhere. I managed to put the vacuum hose back on the vacuum canister tank nipple which was easy coz I have some long surgical forceps and the last hose to the acctuator musta got fried on the exhaust manifold or header! Thanks for your help. As for the oil in the vent line , maybe the transfer case is over full. The oil looked kinda weird - not much viscosity. i think I'll change that while I'm at it. I also read that the vacuum switch can stick open. Only way yo find out is remove and inspect.
    thegawd likes this.
  6. Chesters

    Chesters Well-Known Member 2 Years ROTM Winner Gold Member 1000 Posts

    Al, forgot to mention one thing about that hose, it cannot fall below the TC vent line and also has a breather vent mounted at the upper end of it to keep moisture and crud out, don't just cap it off, it does need to be able to vent in this case.

    Changing the fluids in the TC is never a bad idea, and making sure the level is correct is also good.
    thegawd likes this.

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