I just bought a 93 gmc jimmy 4x4. It has the 4l60E auto in it and when I drive down the freeway it pours fluid out of the vent onto the exhaust. The vent has a hose on it going up to the firewall. I am pretty sure this is the vent for the trans but mabey it is for the transfercase. Either way, it has one of those one way valves on the end of it and it leaks right onto the exhaust manifold. When I first noticed it I got some fluid on my hand and it wasn't very hot ( the only reason I could come up with for it coming out the vent was if it was getting hot and expanding). The trans works great even when the fluid starts coming out, it shifts fine and doesn't slip at all. I have talked to a lot of people about this and knowone can figure it out. Any information or even wild guesses would be greatly appreciated. I live in Phoenix and this is my only truck with A/C and I really need to get it on the road.

 

My parents had a '93 Astro van, I'm not sure if it's the same tranny as your blazer or not but they had what appeared to be the same problem and after months in and out of the shop the mechanic finally found a hairline crack in either the torque converter or transfer case casting, I can't remember which it was. After getting that replaced the van never gave them another problem.

 

I finally got a chance to look it over better last night and found out that the vent actually comes from the transfer case. It has a tee in with another line that goes to the vacum switch on the transfer case ( the one that engages the front axle) I pulled the vacum lines off it and all three of them were soaked. This explains why it has been running rough trans fluid has been going into the vacum line from the motor. So possibly the vacum switch is bad and it is sucking fluid out of the transfer case? I am going to check to see if the transfer case is over full tonight. ( thinking that the seal between the trans and transfer case is bad and the tranny is filling up the transfercase). I haven't driven it much yet so I don't know if it is using trans fluid or not. I don't know what else might be wrong unless it does have a crack in the case.
It has the 4l60E trans and the electronic shift transfercase.

 

I do not think that the vacuum switch can pull fluid out of the transfer case, but I could be wrong. Most likely your rear seal has gone bad.

You will want to make sure that you clear out the vent lines to your HVAC inside the cab as well. All of that is connected and it sucks to be with out heat or a/c...

 

Yea, I don't think it could pull fluid out of there either but I pulled it out to check anyway and the seal looked good and it still has a pretty strong spring on the ball. But it's really tough to tell if there is anything wrong with it.

Sounds like pretty much all the vacum lines are interconnected. When I bought it the a/c only blew out of the defroster and the cruise didn't work because the vacum line on the back of the intak was unhooked. Hmmmm......Mabey this is why it was unhooked. Cause it didn't have this problem when I drove it home.

 

Kyle,

GM has a TSB on the switch. Matter of fact they even redesigned the switch to fix this problem. But I will agree with you that if fluid levels were normal then there would not be a problem. And he should have the rear tranny seal checked for leaking into the transfer case.

 

I know that GM has a TSB on it and although I cannot find the exact one right now, I do not remember it stating that a failed vacuum switch would draw fluid out of a transfer case with the proper fluid level... But I could be wrong cause it didn't apply to my Bravada so I may not have read it as thoroughly...

 

Where did you guys find the info on the tsb? I checked on alldata but I didn't see one. I might of just missed it though.

 

It doesn't come up under my 2k Alldata account either, but I can look it up in my references at home once I get home and reinstall them on my computer. May not be able to get to it until tomorrow afternoon though...

 

OK. I pulled the fill plug out of the transfer case ( finally found the right socket) and almost four quarts of trans fluid came out. Definatly over full. I topped off the tranny and drove it for about 100 miles and then ckecked it again. It lost about a pint and it isn't leaking on the ground. I am just letting it cool off before I check to see if it went into the transfer case. So I am pretty sure it is just the rear seal on the trans.