[donnie_dee]

Howdy everyone, I've been a long time lurker on this site, finding great information on my 1991 Mustang (2.3 L, NA, 4 speed automatic).
This is the first time I've ever needed to ask something so specific though...

Recently (with the help of this forum, of course), I diagnosed a problem with the Transmission Vacuum Modulator... which was causing my ATF level to run down rather quickly, and slipping to occur. I would have to top up every week or two before I did the work. When I finally did it, everything worked quite well. For the last 3 weeks I put A LOT of miles on it, without loosing any fluid...
Today that all changed.
I was leaving my sisters house, casually driving down the street, without accelerating or putting any kind of unusual stress on the motor suddenly I had white smoke billowing out of the exhaust. It did not smell like oil burning, and lacked the distinct blue tinge. It did not however smell like coolant, an odour I am also quite familiar with. I pulled over right away and first thing I checked was the ATF dipstick. It read okay at this point. Engine oil level was fine too, and there was still water in the coolant reservoir. I elected to take my chances getting it home across town, about a 15 min drive. As I drove the transmission began to behave in a familiar way, slipping mildly at first then the worst I've ever experienced by the time I got it in the drive way. At this point checking the stick revealed the transmission was bone dry.
So it is obvious to me that the smoke was ATF oil because
1. transmission went from full to empty and started slipping by the end
2. smoke was thick and white, lingered a long time (hence not water) and did not smell like engine oil smoke or have a blue tint
3. oil was coming out the tail pipe and had a reddish hue
it is also obvious that the vacuum modulator I put in has crapped out after less than 3 weeks.
My questions/concerns are this.
Do you think I could have just had the misfortune of getting a defective vacuum modulator? Perhaps I should have done to the dealer for an OEM rather than an after market? Could there be a bigger underlying problem? Could the extended period of driving with a malfunctioning modulator have caused some kind of damage that resulted in the new one getting destroyed? Did this drive across town total my transmission? Should I be getting ready for a rebuild, or should I calmly just start with a new, possibly OEM modulator and see how it goes?

*also, I am doubtful of the relevance, but about 2 months ago I changed the transmission filter and gasket, and inspected the magnetic filing catcher in the pan on the advice of someone.. it didn't reveal anything compelling.

Thanks in advance for your thoughts!
-Donnie

 

[TOM RENZO]

Well you are experiencing either a cheap part or the engine is letting gas or gas fumes enter the diaphragm. Is your modulator 2 line or single line???? Either way you need a FUME TRAP. I do not know where you can get one Though. They are obsolete by now i would think. Years ago the 360 jeep engine used to blow the distributor cap off the engine. It took me a week to figure it out. The dizzy on that car was lower than the Carb and fumes ruptured the diaphgram. Then the fuems traveled into the DIZZY. When you cranked it over the spark ignited the fumes and blew the cap off. I got hundreds upon hundred of calls about this years ago. People actually thought someone was messing with their cars. Peace TOM:bigthumbsup:bigthumbsup

 

[donnie_dee]

The modulator connects to a single vacuum line, which from what I understand leads to the intake. Could gas fumes really reach the diaphragm on the modulator this way?
I imagine this line connecting some place between the throttle valve and the intake ports, so vacuum could pull the diaphragm out.. or are you saying that exhaust could somehow be entering the transmission at another point, and pushing the diaphragm out?
I've gone to Ford to get a not as cheap replacement modulator and will put it in tomorrow.. and see how it goes.

(BTW, no dizz on this vehicle, it uses the so called "distributorless ignition system")

 

[TOM RENZO]

Not exhaust!!!! The line is connected to the INTAKE manifold. And its possible to get fumes in it, Most likely you bought a chap modulator. The ford unit will work better. But most vacuum operated things are subjected to GAS fuems from the engines manifold. Not as much with EFI but possible. I just threw that in for KICKS AND GIGGLES. But it has happened in the PAST:bigthumbsup:bigthumbsup

 

[donnie_dee]

Put in the modulator from Ford.. it felt like better quality, and of course everything seems to work (for) now.
Just for fun I cup apart the one I pulled out. It's hard to say for sure, but it looks like there may have been a clean tear in the diaphragm.. some sharp edge inside the cheapy one?
Time will tell.
Thanks for your help though Tom.