Automatic transmissions, how do they work, what goes wrong with them, how do I keep it from breaking ?

Car Advice from Tommy...

Hi. The automatic transmission contains gears and clutches that are lubricated by automatic transmission fluid or ATF. ATF is pressurized by the transmission oil pump that is driven by the engine. The pressurized fluid flows through the transmission to engage and disengage the clutches and bands. A valve body, usually located in the bottom of the transmission, controls the fluid flow to the clutches and bands. Clutches are attached to different gears inside the transmission. When fluid pressure is applied to a piston, by the valve body, it pushes on the clutches and locks them together. This allows the transfer of power to the gears to make the car move.

Another major component of the automatic transmission is the Torque Converter. The torque converter is a fluid coupling that connects the engine to the transmission. At slow engine speeds the torque converter slips to allow the engine to continue running even when the vehicle is stopped. As engine speed increases, the torque converter transfers power to the transmission. The inside of a torque converter has 2 fans facing one another. One fan pushes the fluid and turns the other fan, that is attached to the gears in the transmission, much like the wind turns a fan that is not on. The torque converter also has a clutch inside of it that will make a manual connection, between the two fans, when your car reaches highway speed. The most common issue we see with torque converters is shuddering. It will feel like you are driving over rumble strips when the torque converter makes its mechanical connection. This issue can easily be fixed by flushing the transmission fluid with chemicals and a machine that replaces all the fluid.Automatic transmission fluid is red in color when it is new and as it ages it turns black. One of the reasons it turns black is every time the clutches engage and disengage a little bit of the clutch material wears off. These little pieces of clutch material are carried away by the fluid to the transmission filter. The filter keeps the transmission oil pump from picking up the larger pieces, but the microscopic pieces stay suspended. When the pump sucks the oil up again the microscopic pieces get circulated throughout the transmission and can cause accelerated wear. Stop and go traffic greatly effects the amount of material in it the fluid because the transmission is constantly shifting and wearing the clutches.Another reason it turns dark is from too much heat. When this happens, the fluid will start to break down faster and turn color. A transmission cooler is used to cool the transmission fluid down to prevent this from happening. It is usually a small radiator that sits just behind the bumper cover and can become clogged with dirt over time. Some manufactures install a cooler inside the radiator to avoid dirt clogging an external cooler. Having the cooler inside the radiator is ok but the fins can become clogged where the coolant flows through. When coolant starts to break down it create deposits around the cooler and reduce the heat transfer between the coolant and transmission fluid.The biggest transmission failure problems comes from not changing the fluid often enough. A lot of manufactures say the transmission fluid is lifetime fluid and never needs to be changed. The problem with this is that they don’t know how the vehicle will be used. If you do a lot of highway driving the fluid will last longer because the transmission is not wearing the clutches down due to constant shifting. We have seen transmissions fail as early as 70,000 miles and others go over 200,000 miles with no issues. It all depends on how the vehicle is driven. Changing the transmission fluid every 30,000 to 40,000 miles will remove the microscopic particles of clutch material that damage the transmission. These microscopic particles scrape and eventually cut the rubber pistons inside of the clutch packs. This leads to symptoms like delayed forward or reverse movement, jerking, shuddering, or no movement at all.The second biggest issue comes from excessive heat. This can be caused by towing with a vehicle not equipped with a tow package, excessive shifting, or a clogged heat exchanger. These issues cause the transmission fluid to over heat and break down. When this happens the fluid does not lubricate the internal pieces or remove heat from the transmission. This leads to melted seals and massive transmission failure. A clogged heat exchanger can become clogged on the coolant side of the exchanger. Regular flushing of the transmission and the engine cooling system can help prevent this from happening.With replacement transmissions starting around $4,500 installed a little bit of maintenance goes a long way. Reputable shops like ours use top quality flush machines that can extend the life of your transmission. They also may offer a transmission maintenance plan that covers your transmission if it does fail. Our current plan offers $2,000 towards transmission repair if you start the plan before 50,000 miles.