Thats probably why your tranny went in the first place I have had many people through the years my old mechanic included tell me never ever ever change the transmission fluid your asking for it to go by doing that.So I have never changecd tranny fluid on any car I have ever had will add it when its low and have never had any problems with a transmission.The reasoning was that when you drain/refill even though your changing the filter your sturring up metal shavings that have been laying down in the pan not bothering anything.I have lived by that and its always worked for me.
Whatever, maybe you just got good mojo, but I wouldn't count on it. Maybe if a transmission is already on the way out your theory would hold water, because sometimes it's just the oil holding it together (my Dad's Honda Oddity van comes to mind!)
The main thing is, ALWAYS change the filter and wash the pan out with solvent/brake cleaner when changing the transmission fluid. 99% of transmission problems are caused either directly or indirectly as a result of heat. When I was in mechanic's school, we saw a chart showing some tests they did on a dyno correlating transmission life to temperature, which forms an inverse proportion graph. At an oil temperature of 275 degrees the transmission had only an average life expectancy of less than 200 miles. At 125 degrees the transmission life was in excess of 150,000 miles. At 175 degree oil temp the transmission life was like 75,000 miles, and at 200 degrees it was like 25,000 miles. SO, anything you can do to lower transmission oil temperatures will DIRECTLY lead to longer transmission life. Clean oil helps lower temperatures by reducing friction. Clean filters and pans help improve oil flow and lower resistance, and increase heat dissipation, which helps. The best thing you can do to increase transmission life is to install a secondary oil cooler in front of your radiator. They're easy to install and readily available at Auto Parts stores.
Don't believe everything you read in the owner's manuals, either, about transmission oil change intervals. Most newer cars and trucks use synthetic ATF now, many of them 'proprietary' formulas that don't interchange or only interchange with certain brands/makes. MAKE ABSOLUTELY SURE THAT ANY SHOP THAT SERVICES YOUR TRANSMISSION, OR IF YOU ADD TRANSMISSION FLUID TO YOUR CAR, THAT YOU USE EXACTLY THE SAME TYPE OIL SPECIFIED ON THE DIPSTICK!!! I've even seen owner's manuals incorrectly state what type oil to use, so be SURE you check the specified oil stamped or printed on the dipstick to make double sure. Putting the wrong oil (Mercon or Dexron II in a newer vehicle that calls for say, Mercon V (which is synthetic) WILL cause transmission slippage and burn up your transmission! And yes I've seen transmission shops screw up and put the wrong oil in!
The sythetic ATF's are good, but while most manufacturer's recommend the car only have the transmission fluid changed at 100,000 miles or thereabout, I wouldn't advise it. Yes the oil is expensive, especially compared to the old 'regular' ATF's like Dexron II, but changing the oil/filter is the ONLY way to get contaminants out of the system. I would recommend for pickups and SUV's, especially if they do ANY towing, to change the oil/filter at 33,000 miles to 50,000 miles AT LEAST. For cars/minivans, or light trucks/SUV's doing NO towing, I'd recommend changing oil at 50,000 miles AT A MINIMUM.
Transmissions ain't cheap no more, and it's cheap insurance. Good luck! OL JR
PS. Never fall for the old 'found a gear in your oilpan' crap... if you have gear parts in your oilpan, you might as well run it awhile longer-- the damage is done, while you start saving your pennies for a transmission rebuild... LOL
