How long do transmissions last? It's a big question and one that's actually quite difficult to answer. Factors such as maintenance and build quality play a role. Lubrication and heat are also parts of the equation, as are circumstance and fate.
The best way to keep a transmission alive is proper maintenance.
Transmission fluid plays a critical role in how a transmission functions and the car part longevity. Like engine oil, transmission fluid should be checked and changed on a regular basis; however, the interval is different for all vehicles and dependent on the transmission and fluid type as well as use.
Changing transmission fluid is not as simple as changing engine oil and should be handled by a service technician or someone with a thorough understanding of transmissions. Generally, the car is lifted on a hoist, the pan is dropped and the old fluid pours out. This fluid and the pan are inspected for contaminants, such as fiber from clutch discs or any other indication of a larger issue that may be appearing. After a routine check of the exposed components the filter is changed, the pan is replaced and the fluid added to the proper level.
Manual transmission fluid change is usually simpler. Manual transmissions are usually outfitted with drain and fill plugs. The car is lifted, the oil drained, and then refilled with the proper grade specified by the manufacturer.
While maintenance is key to auto part longevity, being aware of any bangs, whines or groans from the transmission, as well as smells, will help head off any problems at an early stage.