Higher mileage automatic transmission that you don't know the maintenance record of . Transmission works perfectly , fluid change / flush or not ? One school of thought says yes , another says no . I personally disassembled an auto trans. & there was gunk hiding in a lot of little nooks & cranny's . I can see the logic behind the school of thought that says don't do anything to cut this gunk loose .
There's also the school of thought that says , bunk , change that fluid and or get a flush , the trans. fluid needs changed . I can also see the logic behind this school of thought . I also have read that lubricants don't wear out , they just get dirty .
There is a man locally that has a shop at his home & makes a living rebuilding auto transmissions . He evidently is good as he has a very good reputation in this area . My father-in-law had a transmission rebuilt by him & he said the man told him it was a mistake to change the fluid in a transmission that had fairly high mileage & hadn't been serviced regularly .
A family member had a ford ranger that needed a transmission . He purchased a salvage yard transmission , installed it & it worked properly . He changed the fluid & filter & the transmission immediately went south . The salvage yard had warranted the transmission so he removed it , took it back & they gave him another one . Did the exact same thing with the 2nd transmission . It worked properly , fluid change & it immediately went south , he parked the truck after that & didn't fix it again .
Now I'm in the same boat with a jeep liberty I bought that needed an engine & I'm in the process of installing a low mileage engine in it . To mess with the automatic transmission fluid or not , that is my dilemma . The transmission is / was working properly when the jeep was parked due to engine problems . As always , input is what I'm looking for & would appreciate .

Just found this article , hope it's ok to post the link .

http://articles.chicagotribune.com/2...-atf-oxidation

If it ain't broke... Don't fix it.

_________________
2004 KJ 3.7 Limited:
IRO WJ Upper Arm -- WJ Rear LCA's -- Rear Driveshaft Spacer -- JBA Upper A Arms -- 4 inch Lift -- 265/75/16 4" B/S -- WasherBottle Relocate -- Custom High Mount Intake -- Carpet Delete -- Homebrew Winch Bumper -- Warn VR8000 -- Homemade Plow -- Pinch Weld POUNDED -- POR 15 inner fenders --

And if your going through the trouble of putting in a lower mileage engine, why wouldn't the words rebuilt (like new) transmission be the first to cross your mind?

Just my $.02

_________________
2004 KJ 3.7 Limited:
IRO WJ Upper Arm -- WJ Rear LCA's -- Rear Driveshaft Spacer -- JBA Upper A Arms -- 4 inch Lift -- 265/75/16 4" B/S -- WasherBottle Relocate -- Custom High Mount Intake -- Carpet Delete -- Homebrew Winch Bumper -- Warn VR8000 -- Homemade Plow -- Pinch Weld POUNDED -- POR 15 inner fenders --

Pull the transmission dipstick and get a good whiff.
If it smells bad the fluid and filters need to be changed. To me, nothing smells worse than burnt transmission fluid.
Look at the color of the fluid. Any color other than red is bad.
brown = bad
black = really bad

The idea that changing the fluid on an old automatic transmission causes it to break is false.
Most likely the transmission already had a problem. Changing the transmission fluid was probably the first step in trying to fix the problem.
Flushing the transmission with some sort of chemical solvent is bad.
It can knock loose chunks of stuff that will block a passage somewhere.
And when you drain and re fill it, you can never be sure that you got all the solvent out.
I'm a big fan of the types of transmission flush machines that tie into the cooler lines, where the transmission pumps out all the old fluid into the machine and new fluid gets pushed in. But the problem with this is that in the process your filters never get changed.

The best way to take care of an automatic transmission is by doing regular fluid and filter changes. Change that fluid before it gets ugly.

_________________
U.S. Army Retired