I just took my recently purchased 95 Blazer for a ride. It has an automatic transmission and I just replaced the 4WD switch which was broken. It rides fine in 2WD but as soon as I switched it to 4WD, transmission fluid started pouring out of a rubber hose on the toward the top rear of the engine compartment (passenger side).It looks like a vacuum hose and last week my mechanic said it was just a vent hose. Could he be mistaken or should this hose be connected to something? I don't want to drive it until I understand if there's a problem. Thanks

 

The first thing I would recommend is pulling the fluid fill plug on the transfer case. It is quite possible that the rear seal on the transmission has failed, filling the transfer case. If you get fluid out of the fill hole (upper plug), then you will need to replace the rear seal on the back of the transmission by pulling the transfercase.