One of the most common transmission types in use in cars and trucks today is the automatic transmission. While the transmission is a complex unit of gears, clutches, and a pump, some simple things can cause the transmission to stop functioning correctly. Fortunately, these are not difficult to fix.
Dirty Transmission Filters
Inside your automatic transmission, an oil filter separates dirt and debris from the transmission oil pumped through the system. The oil filter is a wire mesh unit, and it is typically mounted just below the transmission valve body inside the oil pan.
Changing the filter requires a technician to drain the oil from the transmission, remove the oil pan, then remove the filter. While the oil pan is off the transmission, it should be cleaned to remove any sludge sitting in the bottom of the pan. It is also a good idea to check for metal pieces that can indicate damage inside the unit.
A dirty oil filter can cause the transmission to shift sluggishly or be erratic when you are driving. Often it will bang into gear and could feel like it is slipping at stoplights or anytime you are starting from a standing stop.
Some manufacturers will specify a filter change at around fifty thousand miles but refer to the owner's manual in your vehicle to determine when yours should be done or take it to a transmission repair if it is not working correctly.
Old Transmission Oil
The oil in the transmission is essentially a lightweight hydraulic oil, and it will break down over time. Once the oil becomes dirty and thin, it will not work as well in the system, and it is a good idea to change the oil completely. You can drain the oil and refill the transmission, but that will leave some in the oil cooler and lines that will get pumped in and mixed with the new oil when you start the vehicle.
Flushing the system entirely is the best way to ensure all the dirty or old transmission oil is out of the system, and any transmission repair shop can take care of this when they change the filter. Old or contaminated transmission fluid or oil will contribute to poor shifting, sluggish starts, and it can cause the transmission to overheat.
The oil in your automatic transmission carries heat away from the internal components and through the oil cooler, but it may not work effectively when it is thin and dirty. The result is often a transmission that runs hotter than it is designed to.