Transmission Modulator 94 2wd | Ford Explorer - Ford Ranger Forums - Serious Explorations
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Transmission Modulator 94 2wd


June 12, 2012
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Year, Model & Trim Level
1994 Explorer
I am seriously losing tranny fluid through my vacuum line and through my intake manifold and hench mixing with fuel, air, spark, AGAIN!!!!! Exuast smells like trans fluid and looks light blue in color on a hot Virginia day. I just replaced the modulator two weeks ago. The same problem has returned. Yes, I remembered that pin.

I really need to take a good look from top and bottom of the modulator to see if I placed the modulator in correctly. Seemed straight forward enough, but as experienced has taught me straight forward repairs on Fords are not really straight forward! I read the posts on how to access the modulator so I have no questions about that.

I do have some questions on the modulator itself. WHAT IS IT'S PURPOSE(S)? Does it let in the vacuum and keep the trans fluid in? If that's the case I prob have another bad modulator! What are the chances of frying a new modulator? Could I have recveived a bad modulator from Autozone? Should I get one from the Ford parts dealer? Could the problem be inside the trans in vincity of modulator? Are there tell tale signs if modulator is bad other than the fluid that is evident in the vacuum line?

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The vacuum tugs on a diaphragm - kind of like the diaphragm in a vacuum operated EGR valve or a fuel pressure regulator, if you're familiar with that. If the diaphragm ruptures/leaks, vacuum will suck up tranny fluid into the intake.

As far as I know the modulator can't be put in wrong; it should work in any rotational orientation. If it wasn't fully seated then leakage would be around the body of the modulator, not out the vac line. The only way for tranny fluid to get into that line is through a damaged diaphragm.

All signs seem to point to a crummy vac mod. Try a better quality one. I have noticed Autozone often likes to only carry one (cheapo) version of a part. Try O'Reilly Auto Parts if you have one. If not, maybe NAPA or somebody else can give you options. When I bought my modulator from O'Reillys there were several options, including a cheapo, a better quality unit with warranty, an adjustable unit, and a Motorcraft replacement.

I got the better quality one for about $13, made a replacement pin out of a drill bit, and it's worked great ever since.

Welcome to this forum! It sounds like they gave you a bad modulator. Maybe somebody returned it, and they sold it to you. Did the package have signs of being opened, finger prints or transmission fluid?


:thumbsup: Upon further review, I noticed a clamp that was not tightened all the way. Apparently, the pervious owner sawed off the trans cooling lines for whatever reason adjacent to the oil pan. He used heavy duty hose where the inside diameter = outside diameter of the cooling line with hose clamps; fair enough. When I replaced my modulator, I noticed those rusty clamps needed changing. I replaced them alright but I did not tighten them tight enough. As a result, trans fluid all over the exhaust which explains the light blue smoke from the rear end (vice from the inside of the exhaust pipe) and oil/sut on my tailgate & window. BTW, the modulator I replaced two weekends ago, is still good - NO TRANS FLUID from the vacuum line.

I will keep in mind to get a better quality modulator when it does go bad. Thanks y'all!!!!!!

Thanks for the update!