have a 1994 Bronco with the E4OD. I had the transmission rebuilt about 12,000 miles ago (the truck has 128,000 miles on). The transmission was rebuilt with all the updates, new HD torque converter, big cooler, and improved parts. Anyway a few weeks ago I was about to embark on a trip to the beach, and I noticed that it was shifting very hard on the 1-2 upshift, and the torque converter wasn't locking up when it was supposed to, and when it did lock up, it was pretty violent with a notable thud when it shifting into and out of overdrive. I thought that the transmission had gone into its failsafe mode and was increasing the line pressure greatly. I checked the dipstick and it looked a little low. So I went down to my local Auto Zone and foolishly bought two quarts of Mercon V semi-synthetic. For some reason I thought that I heard that Ford issued a TSB stating that it was okay to use Mercon V in the E4OD, which I now realize they did not. Anyway it shifts fine now. But my question is, will the two quarts of Mercon V be enough to do this transmission in? I haven't noticed anything dramatic happening since dumping the Mercon V in. Is it a no harm/no foul situation, or would it behoove me to get it flushed ASAP?

 

Its OK to use Mercon V in a Mercon Tranny. My Tranny (same as yours) is flushed and re-filled with Mercon V from the dealership.

 

Not according to Ford it isn't. Some dealers will put MERCON V where it doesn't belong, but that does not make it right.

Expect to rebuild your transmission a bit earlier. MERCON V will kill a transmission that needs MERCON, but it will take a while.