should i change the tranny fluid on an expidition with 140k that has never been changed before?
Yes. You should have changed it long ago. Better late than never.
Don’t believe the old wives’ tales about fluid changes resulting in transmission failure. Your transmission might still fail after the fluid change, but that would have happened anyway, simply because the fluid change was deferred for so long. As mcparadise said, “Better late than never”.
Of course you should. It is a little late, but better now than not at all. There is a myth about about this. It goes along like: My father had the fluid changed and the transmission needed to be replace a few weeks later. Same thing with my brother-in-law and he got one of them transmission flush things." What really happened is the same that may now happen to you. It should have been done long ago. I would be surprised if you are not now sensing that there is a problem with your transmission and want to go for the Hail Mary pass. Go for it. It might work for you. But don't come back and say it failed because you got the fluid change. [b] If it fails, it will be cause of the fluid changes it did not get. [/b]
What does the owner’s manual say in the maintenance schedule? I’d guess it’s at least 40,000 miles late, but you certainly should change it.
Drop the pan, clean it real good, change the filter and refill. Do it now and do it every 25-30k miles.
Does it have a torque converter drain plug? Many RWD Fords before ca. 2000 did. If so, drain that as well. Reset the PCM by disconnecting the battery or pulling the PCM fuse to get the PCM out of the habit of compensating for the damaged fluid.
I feel disadvantaged here, a little, because I don’t know what transmission or model year we are considering.