What should be changed to ensure good transmission life after replacing an automatic transmission?

For ensuring good transmission life after replacing an automatic transmission, the appropriate action is to change the transmission fluid. This fluid is vital for the operation of the transmission, as it acts not only as a lubricant but also as a hydraulic fluid that allows the transmission to function correctly.

After a transmission replacement, old or contaminated transmission fluid can lead to premature failure of the new transmission. Fresh transmission fluid helps to ensure that the internal components are properly lubricated and that the transmission operates smoothly. Additionally, changing the fluid helps to remove any debris or contaminants that may have accumulated during the replacement process.

The other fluids mentioned, such as engine oil, brake fluid, and coolant, while important for their respective systems, do not directly impact the performance and longevity of the automatic transmission. Therefore, focusing on the transmission fluid is crucial for maintaining the reliability and performance of the newly installed transmission.