It all depends on who you talk with. Often someone starts noticing problems or symptoms out of the ordinary, and they think a flush will ward off any developing problems. When the problem gets worse or turns into a real problem, they blame the flush and / or the mechanic. If a mechanical problem was developing, such as a worn thrust bearing or worn rubber seal, new fluid isn't going to fix that.
In other cases, it is believed with high mileage transmissions, the friction material has worn off the clutch plates and is circulating with the fluid. That grit helps the plates lock up when that clutch pack is applied. A simple fluid and filter change only removes and replaces about half of the fluid, so much of that grit is still in there. The flush gets all the old fluid out along with all that circulating grit, then the plates have a harder time grabbing when they're applied. That results in slippage and the need to rebuild the transmission. The flush did not cause the slipping. It removed the debris that had been preventing it. I'm not entirely convinced of this story, but I've heard it repeated by multiple transmission specialists. My own experience with clutch material flaking off was it tore up the rubber lip seals, then the clutch packs were not able to apply with enough fluid pressure to prevent them from slipping. That slippage multiplies the clutch plates' inability to grab. Overheating clutch plates and burned fluid are the result, and that leads to more internal damage.
The transmissions on a lot of newer vehicles do not require periodic service like they did years ago. Filter and fluid changes every 36,000 miles were common, and fairly easy to do. Today most transmissions don't even have a dip stick or a simple means of filling or adding fluid. The best place to start is with your owner's manual. Next would be at the dealership. I inquired about a fluid and filter change for my 2014 Ram at the dealership I used to work at. The people there chuckled and said, "see ya at 200,000 miles". That's the good news. The bad news is these high-mileage transmissions require special fluid. Some fluids cost almost as much for a gallon than the entire filter and fluid change cost in the '90s.
The bottom line is if a mechanical problem is developing already, neither a flush nor a fluid and filter change will solve that. If there is no problem now, a flush is likely not a good value as it isn't going to prevent a problem from developing. Be aware too recommendations from the manufacturer can vary widely depending on the engine or transmission used in your vehicle. I found one model in one year that had over a half dozen different recommendations for fluid type and change intervals based on three engine sizes and two transmissions that were used, and they were different depending on which rear axle was used.
Years ago there were just two or three different transmission fluids, and using the wrong one usually led to problems. Today there are dozens of special formulations and each manufacturer gets pretty specific in what they want used.
Here's links to some articles that might give you a better idea of what is appropriate:
https://www.2carpros.com/articles/how-to-check-and-add-transmission-fluid
https://www.2carpros.com/articles/how-to-service-an-automatic-transmission
https://www.2carpros.com/articles/7-signs-of-a-bad-transmission-how-to-identify-transmission-problems-in
Let me know if I missed something or you have more questions.
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Sunday, July 30th, 2023 AT 6:41 PM
