Tranny vac modulator failure

[drtidmore]

I am still finding side effects of the resultant backfiring due to a failing fuel pump of a couple of weeks ago.  The latest first raised it head early this past week. It was a chilly morning with the dew point almost the same as the outside temp when I started up the Reatta and there was a massive cloud of whitish vapor that poured out of the rear of the car.  I immediately opened the door to smell and found NO odor, so I wrote it off as condensation due to the dew point/temp since it stopped within a couple of seconds.  Then a couple of days later on my way back from the daughter's house, as I decelerated the car from highway to service road speeds, I felt a shutter and then as I continued to a complete stop, each downshift of the transmission was hard and rough but upshifts on acceleration remained smooth.  I had a stop to make before getting home, and when I restarted the car, the whitish smoke returned and this time the outside temp was in the mid 80s so NO chance of condensation.  I got out and given the rough downshifting, pulled the dip stick and found the fluid was barely showing.  

 

Then it hit me.....vacuum modulator failure!  The modulator on my Reatta was factory original and had been working flawlessly previously.  

 

On removal of the modulator, I expected to find a slight leak thru the modulator, but found that I could easy blow air all the way thru it, which explained the loss of the tranny fluid.  Now can I say with certainty that the backfires caused the vac mod failure, no, but my theory is that the diaphragm in the modulator was likely a bit brittle already and the pulse of pressure on backfire blew it out. 

 

A new modulator (easy replacement) a quart of Dextron VI and a preventative treatment of Blue Devil Transmission Sealer and all is once again well.  

[2seater]

It happened to me too, although in a different way. I figure it was boost pressure from the turbo installation that got to it. I think I remember seeing some where that the oem modulator can only take 5-6 psi positive pressure? It drinks a surprising amount of fluid through that line when it fails. At that time I had no catalytic converter and it would stink to high heaven too. An aftermarket adjustable model appears to have a greater resistance to boost.