why does my transmission "vent"

[cobb535]

Recently I replaced the transmission in my 89 535i with a "good" one from my patrs car. The donor transmission had good unburnt fluid in it and had yellow crayon markings on it like it came from a junkyard or had been rebuitl. I replaced the filter and fluid as part of the install. The trans works fine EXCEPT fluid is coming out the vent ? on the top rear of the case which proceeds to drip on the exhaust and deliver smoke from under the car. I used Dextron III and bentley specified Dextron II. The fluid had dropped from nearly full to nearly add in about 500 miles. I suspect fluid foaming. Any sussgestion of a cause or fix eg. different type of fluid or additive. The transmission sat for a little over a yrear before being used.

[gale]

Probably a cracked or broken vent dammit (item 17)

http://www.nmia.com/~dgnrg/zf_vent.jpg

I did a "Winfred" on my son's 535i this past winter & broke the tip off of the vent tube when we rolled it over at the spray wash. Now that yours is installed, it's going to be a bit of a pain to replace but you can remove the tail housing with it in the car. I don't have any pic's of the vent but if you scroll down to the bottom of this link you'll get an idea of how to get to it.

http://www.nmia.com/~dgnrg/page_43.htm

[cobb535]

Bump .Any other ideas? I'm going to replace the vent assembly. anything else to check when I have the rear transmission casing off?