Well, it depends. Automatic transmissions can last as long as your car does when it is serviced periodically and properly. Although this doesn’t guarantee you will never need to replace your automatic transmission, it certainly increases the odds — GREATLY.
It is also important to note that some particular vehicles have a more problematic automatic transmission than others. Some brands seem more prone to breakdown than others too.
Also the older the car, the more potential you can have automatic transmission problems.
The automatic transmission relies on proper lubrication and consists of many moving mechanical parts. As you can imagine, the constant grinding of metal to metal WITHOUT proper lubrication will create two problems. One, it wears down the internal parts. And, two, those flecks of ground parts float around and exacerbate the problem further.
We recommend that you follow your car’s manufacturer recommended automatic transmission service intervals. These services drain the old fluid that gradually becomes ineffective at protecting the internal mechanical parts. If you are not sure, and you want to err on the side of safety (and a long-lasting automatic transmission), we recommend a service every 24,000 miles or two years whichever comes first — unless your manufacture recommends a shorter interval.
Automatic transmission services include draining the old ineffective fluids, cleaning the transmission system out, and replacing the fluid with fresh, protective fluid. It’s similar to what you do with your engine’s oil and filter replacement. And, with the cost of a new or rebuilt transmission rivaling the price of a new engine, it is just as important.