Have any shops told you about the 100K+ Transmission Myth? Apparently every mechanic recommends that you do not change transmission fluid if it has never been serviced before 100,000 miles. Claiming that changing it will cause the transmission to slip or cease to work all together. Is there truth to this notion?

​​​​​​Have any of you guys personally known of somebody never changing their transmission fluid till after 100,000 miles then doing a drain and fill with zero issues?

 

My wife bought a new 1992 Honda Accord auto in October of 1991. We sold it about 3 years ago with about 250,000 kms on it. At 200,000 km I did a timing belt job on it and changed the trans fluid for the first time. I used genuine Honda fluid. There was a performance improvement in shifting. We had zero problems from 200,000 km to 250,000 when we sold it.

Of course this vehicle was from the generation of Accords that were produced when Honda knew how to design and build reliable transmissions and installed them in their Accords. Relatively soon after, however, for some unexplained reason Honda "forgot" how to make bulletproof auto transmissions.
https://wheels.blogs.nytimes.com/201...-persist/?_r=0

(It's probably the same reason that after many decades of making them, Ford "forgot" how to make cruise controls that wouldn't bust into flames. Unraveling the Mystery of Ford?s Fire-Prone Switches - The New York Times )

 

I wonder if it is better to do a drain and fill or a flush once you have gone over 100,000 miles.

 

....you should have been changing your fluid before you get to that point. I'm at 195k miles, changed (flushed) every 45k miles....no issues.

 

Received advice from a Mitsubishi Master Tech they advised just a drain and fill, and never do a flush to the Automatic Transmission.

 

for ATF...the service manual states that you do a flush. And by flush, I mean you pull the tranny radiator return line and let the tranny pump out fluid. Refill. Let tranny pump fluid (old) out until it flows clear (new). Refill. You get all out except what is in the torque converter, which is not much.

 

Years ago, I picked up an old '91 Sentra for $100 and drove it around as my beater (175k miles on it). I drained the blackened trans fluid and replaced the filter/fluid/pan gasket. Within a few hours the insanity began, crazy shifting or holding in one gear till the tach was at over 5k.

The theory behind the myth is: Tranny fluid is as much detergent as it is oil, as a matter of fact you can use it as a cleaner. So when you have really old fluid that has been allowed to create deposits in certain channels, disturbing those deposits can create a problem; because the nice new fluid starts to loosen the old crud and now that crud is stuck in a passageway or at a valve opening and causing a restriction of fluid. Then the shifting gets crazy as pressure tries to move this junk around until hopefully, it finally, gets stuck in the filter.

I would have said it's a myth too, until I ended up in this very same situation. Had to buy a couple of parts from the Nissan dealer to get it going again and it would still run up 1st gear pretty high.

For my Outtie, I do every 35-45k miles and pump out with the cooler hose removed, it's easy to get to with all the under-trim off the car. Thankfully Mitsu skipped the filter so no need to open the pan.

Cheers