The under belly of a 2000 4x4 Blazer is wet with Trans. oil. The level is ok on dipstick, so maybe it just started,,, or has just shown up. The plastic cover shields on the left side catch the the oil, and so it puddled in several places. I have read about a front seal failure, that allows TR fluid to over fill the transfer case, if over full is it somehow forced out a vent or something ??? I also read about a transfer pump ring, knocking a pin hole in transfer case housing,,,, but I am thinking that is a different transfer case model, then what is on a Blazer [ like maybe that problem is a beeg truck trans and TR case problem ] So,,,, oil leak,,, almost looks like it is spraying or misting,,,, mostly on right side,, but follows covers on left side,,,, sort of a 'bomber' class vehicle,,, so may not merit a lot of $$$$$. Any ideas or thoughts would be appreciated. I washed it all off to try to see a source after a short drive.

 

Check the vacuum vent hose to see if there is transmission fluid in the tube. To find it, on the upper left side of the transfer case just above the front drive shaft output is where the vacuum switch connects. There will be 3 vacuum tubes connected to this switch, and one of them is the vent tube. It will vent somewhere just above the transfer case.


If there is fluid in the tube then the front input seal on the transfer case is bad and is allowing transmission fluid to be forced into the transfer case overfilling it. You'll need to replace that seal, and need to replace the vacuum switch too. Depending on how far into the vacuum system the fluid has gotten you may need to replace all your vacuum tubes and heater controls. Transmission fluid in the heater controls will kill them.

 

I replaced that Vac switch on the trans/ transfer case last year,,, just a week ago, I replace the actuator under battery,,,, the old switch was letting oil sneak out, and finally killed the actuator,,,,,,,,, not sure when the actuator failed, as the 4x4 part gets very little use. plus the spiders gears went out too,, so that slowed down the use-age too. Spiders fixed now. But I will re-check all that,,,,,also.

 

Update: The transfer case was over-full a quart of oil came out of fill hole, then another quart when I removed drain plug. Refilled with about a quart, until it came back out of fill hole. So,, the transfer case seal that mates up to transmission is letting transmixer fluid leak into transfer case,,, how fast ??? I do not know yet,,,, when the transfer case gets too full, would that cause the fluid to ooze or leak all over the under side of Blazer ??? Is there a mechanical problem with letting it leak into transfer case,,,, since it is a low use bomber vehicle, why not just drain it once or twice a year to keep the underside dry ?

 

I guess my question is,,,, what is the harm of too much fluid in the transfer case,,,,,, ok,, oil is leaking out somewhere, but if that maybe is just coming out of the vent,,,,,,,,,,,,,,, so a longer vent hose may prevent that ??? Again, an ole' bomber vehicle,,, but do not like oiling the driveway,,,,,,,,,,,,,

 

The input shaft seal on the transfer case has failed. Timken seal # TMS 3173. Transfer case to adapter gasket fel pro # FEL 72769. Under $30 for both if you have a 3-button system. If you remove the seal housing, make sure it goes on the same way it came off. There is a divot in the housing that lines up with a hole in the T case for oiling the input shaft bearing.

That failed seal is allowing transmission fluid to overfill your transfer case. As El Beautor mentioned, the transmission fluid will ruin your vacuum system including heater controls if you don't have the auto climate control. Keep an eye on the transmission fluid level as it will go down. Good job on your diff. Those gears were BAD.

 

sooooooooooo, can't blow off the transfer case seal,,,, ugh,,,,, my brain is wondering how too much oil in the transfer case gets into the engine vacuum system,, I get it, if that 3 port switch fails,, [ which was replaced] ,,,,, why would the engine draw a vacuum out of the transfer case,,,,,,,,,,, will rest over the weekend,, and consider the seal job next week,,, thanks Rusty-N , yup the gears were used up, that is true,,,,, not such a bad job, thanks to you guys, and you-tube.

 

not sure but I think as soon as you engage the 4 wheel vacuum it will pull fluid up to your heat/cooling vent system. Anyone can correct me if I'm wrong

 

sorta' what the guys are saying newguy,,,,, seems bizarre that engine vacuum could suck up fluid,,,,,but only if transfer case is too full,,,,, ????? almost easier to disable transfer case vacuum,,, use a cable pull to engage front axle,,,,, sort'a like lock out hubs control from the cab,,,,,again,, most of the time I do not Rube Goldberg things,, but this is a part time bomber class vehicle,,,, not a daily driver,,,,

 

By over filling and no excess room to flow the oil heats up, oil expands, hence spewing out the vent. Even in 2WD the O ring in the switch fails by having oil pressure and along with vacuum against it. The switch failing is the first fail it will also lead to case gaskets, seals for the drive shafts failures leading too eventually transfer case failure